Posts Tagged ‘rifling’
How does rifling twist rate affect velocity and/or accuracy: Part 7
by Tom Gaylord, a.k.a. B.B. Pelletier
Part 1
Part 2
Part 3
Part 4
Part 5
Part 6
This is Part 7 in this lengthy test series that looks at the effects of the rifling twist rate on both velocity and accuracy of a pellet rifle. Today, we’ll look at the 1:22 barrel, which means the pellet will turn once in each 22 inches of barrel it traverses. Of course, the Lothar Walther barrel in the .22-caliber AirForce Talon SS rifle I’m using is only 12 inches long, so the pellet doesn’t even turn one time before it leaves the muzzle, but that twist rate sets the pellet in rotational motion as it flies through the air to its target. The rotational speed will be less than what the 1:16 factory barrel imparts, and much less than the 1:12 barrel we have also tested.
Dennis Quackenbush made the two custom barrels I’m testing against the factory barrel with its 1:16 twist. So far, we’ve tested velocities with 2 different pellets at 3 different power settings for all three barrels (see Parts 2 and 3), and I did a short analysis of those tests in Part 4. Then, we tested the accuracy of the custom 1:12 barrel with both pellets at all 3 power settings at 10 meters, and again at 25 yards. Next, we did the same thing with the factory barrel.
Today, we’ll look at the accuracy of the 1:22 barrel with both pellets at all 3 power setting at 10 meters and again at 25 yards. In the next report, I’ll summarize the entire test to this point for you — comparing all 3 barrels for both power and accuracy. After that, I plan on testing all three barrels for accuracy at 50 yards. At that distance, the pellets will be spreading and accuracy benefits should show up vividly.
On to today’s test — the 1:22 twist-rate barrel.
Ten-meter testing
First up was the 14.3-grain Crosman Premier pellet. I had to remove and remount the scope, and the pellets were now striking to the left and low of the bullseye, but I left it there because where the pellets land doesn’t really matter in this test.
Ten pellets made a group that measures 0.258 inches between centers. Besides being tight, it’s a very round group, indicating the pellet likes this twist rate and power setting.
Ten Premiers on zero power made this nice round group at 10 meters. It measures 0.258 inches between centers.
Next came 15.9-grain JSB Exact pellets on zero power. They also made a round group, but it was larger, at 0.324 inches. This is still a very nice group, but not as nice as the Premier group on the same power setting.
Ten 15.9-grain JSB Exact Jumbos on zero power made this group at 10 meters. It measures 0.324 inches between centers.
Next, the power was dialed up to 6, and I shot a second group of Premiers. This time, the group was wider than it was high and measured 0.293 inches between centers. That’s smaller than the previous group of JSBs but slightly larger than the Premiers on the zero power setting.
Ten Premiers on power setting 6 made this group at 10 meters. It’s more horizontal than vertical and measures 0.293 inches between centers.
Following that, I shot 10 JSB Exacts on setting 6. They gave a group that is more vertical and measures 0.309 inches between centers.
Ten 15.9-grain JSB Exact Jumbos on power setting 6 made this group at 10 meters. It measures 0.309 inches between centers.
Easy loading
I noticed at this point in the test that both pellets were loading very easy into the breech. I wouldn’t call them loose — just very easy to load.
It was time to dial the power up to 10 and see what happened. Premiers went first, and 10 of them went into 0.288 inches. That’s just slightly larger than the first 10 on zero power.
Ten Premiers on power setting 10 made this group at 10 meters. It measures 0.288 inches between centers.
And, finally, I shot 10 JSB Exacts at 10 power. They spread out more than expected, giving a group measuring 0.53 inches at 10 meters. That was by far the largest 10-meter group.
Ten 15.9-grain JSB Exact Jumbos on power setting 10 made this group at 10 meters. It measures 0.309 inches between centers and is the largest 10-meter group made by the rifle.
What I see here is that Premiers are very stable in the 1:22 barrel. There is little difference in group size at any power setting. JSB Exacts, on the other hand, get progressively worse as the power increases. If we see this much dispersion at 10 meters the difference should be even more visible at 25 yards.
25-yard testing
First up at 25 yards was the Crosman Premier with the power set to zero. The 10-shot group landed very low on the target paper, and measured 0.671 inches between centers.
Ten Premiers on power setting zero made this group at 25 yards. It’s very low on the paper and measures 0.671cinches between centers.
Next, I tried 10 JSB Exacts at the zero setting. They were horrible — making a vertical group measuring 1.949 inches between centers. I won’t shoot this pellet at this power at 50 yards because they would go off the paper!
Ten 15.9-grain JSB Exact Jumbos on power setting zero made this 1.949-inch group at 10 meters. That’s all for this pellet at this power setting.
Next, the power was increased to 6 and Premiers were loaded again. Ten of them made a horizontal group that measures 0.845 inches between centers.
Ten Premiers on power setting 6 made this group at 25 yards. It’s horizontal and measures 0.845 inches between centers.
Then it was the JSB pellet’s turn. Ten Exact Jumbos landed in 1.797 inches, which is a little smaller than the group when the power was set to zero. If I try to extend this pellet and power setting out to 50 yards, I’m very likely to get a 7-10-inch group.
Ten 15.9-grain JSB Exact Jumbos on power setting 6 made this 1.797-inch group at 10 meters.
Finally it was time to try the pellets on power setting 10. Here they would be traveling their fastest, which means the spin rate would also be highest for this barrel. According to the theory, the groups should get smaller.
Premiers went first, and 10 of them landed in a group measuring 1.082 inches between centers. That’s larger than both groups that went before. Since the velocity increased, the Premiers spread out. Interesting!
Ten Premiers on power setting 10 made this group at 25 yards. It’s horizontal and measures 1.082 inches between centers.
Finally, it was time to try the JSB Exact Jumbos on power setting 10. This time the theory did play out as expected, because 10 pellets made a group measuring 1.172 inches between centers. It’s smaller than the group from both of the lower power settings, and those groups decreased in size as the power increased.
Ten 15.9-grain JSB Exact Jumbos on power setting 10 made this 1.172-inch group at 10 meters.
Conclusions
Premiers behaved differently than JSB Exact Jumbos in this test. They did not become more accurate as the velocity increased, and I think I can suggest a reason why. JSBs are longer than Premiers. Premiers measure 0.269 inches in length, while JSB Exact Jumbos measure 0.296 inches in length. At their widest, which is the skirt, Premiers are 0.220 inches in diameter, while JSBs are 0.222 inches across. So, JSBs are longer than Premiers, in relation to their diameter, and that makes them harder to stabilize.
The JSB Exact Jumbo on the left is longer than the Crosman Premier on the right. That makes it harder to stabilize and it needs to spin faster.
That was one of the problems I had with the .22 Hornet centerfire rifle I reported on last week. It shoots its bullets very slow, relative to other .22 centerfires, yet the twist rate is 1:16, where other .22 centerfires are 1:12, or in the very specialized instance of the .223/5.56mm, anywhere from 1:7 to 1:12. That’s why I’ve been writing about these rifles — so we can all gain an appreciation for how twist rates affect accuracy. The .22 Hornet can only do its best with short, fat bullets of relatively light weight. Now, you see the same thing in a pellet rifle.
Today, we see a very dramatic result of how the twist rate affects accuracy. We learned in our test of the smoothbore pellet gun that while a gun may be accurate at 10 meters, it may fall apart at 25 yards. Today, we see that in a rifle that has a very slow twist rate doing the same. If we wanted to use this twist rate, we would need to shoot only very short pellets so they could stabilize. See how it works?
Next, I’ll write up a summary article of the test to this point so we can get a grip on all the data that’s been generated. Of course, it’s all here for you now. All you have to do is go back and look at the results of all the testing to see how the twist rate affects both velocity and accuracy.
Following the summary report, I’ll test all three barrels at 50 yards.
How does rifling twist rate affect velocity and/or accuracy: Part 6
by Tom Gaylord, a.k.a. B.B. Pelletier
Part 1
Part 2
Part 3
Part 4
Part 5
This is the sixth part of a very long test in which we’re looking at the effects of the rifling twist rate on accuracy and velocity. If you have landed here and not read the first 5 parts of the report, I advise you to do so before reading today’s report because I’m not repeating a lot of what went into this test.
I’m using an AirForce Talon SS rifle in .22 caliber because it’s accurate and also because the barrels are easy to change. Dennis Quackenbush has made two barrels with twist rates of 1:12 and 1:22 for this rifle, but today I’m testing the Lothar Walther barrel that comes standard in the gun.
Today, we’re looking at the accuracy of the factory barrel that has a 1:16 twist rate. I’ll shoot 10-shot groups at 3 power levels with 2 different pellets at 10 meters and 25 yards. That means I’m shooting the rifle 120 times for today’s report. Some of you have wondered why it takes so long between reports — this is the reason.
What you’ll see in today’s report was actually shot on two different days because I cannot maintain concentration for 120 continuous shots. So, I shot the 10-meter targets on one day and the 25-yard targets on another. All shooting is off a rest, to take as much of the shooter out of the equation as possible.
Ten-meter testing
First up is the 14.3-grain Crosman Premier pellet with the rifle’s power set at zero. Ten pellets made a group measuring 0.495 inches between centers. If you’re interested in the respective velocities of each pellet at the various power settings, you can find that in Part 2.
Ten Crosman Premiers went into 0.495 inches at 10 meters on zero power.
Next, I fired 10 15.9-grain JSB Exact pellets on the same power setting. The group measures 0.10 inches between centers. That’s for 10 shots! Don’t tell me that a Talon SS isn’t accurate!
JSB Jumbos were much tighter at 0.10 inches. That’s 10 shots into one-tenth of an inch!
Next, the power was dialed up to setting 6, and I shot a group of Premiers. To see how the power settings are calculated, look at Part 2. Ten pellets made a group that measures 0.404 inches between centers.
Ten Premiers went into 0.404 inches at 10 meters on power setting 6.
Then, JSBs were shot at the same power setting. This time, they landed in a group that measures 0.092 inches between centers. This is better than a lot of 10-meter rifles can do for 10 shots at the same distance. People will argue that they can do better, but it’s always a 5-shot group they show.
Now, THAT is a group! Best one of this test and better than many 10-meter target rifles, it’s 10 shots on 0.092 inches. It looks vastly smaller than the other small group above, but this one has more paper that closed back on the group than the first one.
Finally, we come to power setting 10. Premiers grouped 10 pellets in a tight 0.247 inches. This group is very round, indicating the barrel likes this pellet at this power level.
On power setting 10, Premiers grouped in 0.247 inches. Impressive!
JSBs at power setting 10 finished the 10-meter testing. They landed in a group measuring 0.299 inches between centers.
On power setting 10, the JSB pellets opened back up to 0.299 inches. It’s still pretty good.
25-yard testing
Now it’s time to move back to 25 yards and test everything again. First up is the Crosman Premier at power setting zero. Ten made a 0.48-inch group.
At zero power and 25 yards, 10 Premiers made a 0.48-inch group.
JSBs came next. On power setting zero, they made a 0.571-inch group.
On setting zero, 10 JSB Jumbos went into 0.571 inches.
Then, the power was dialed up to 6, and Premiers were fired again. Ten went into a 0.654-inch group. That was the largest group fired with the factory barrel in today’s test. This group was also spread very horizontal.
Premiers opened up on power setting 6 at 25 yards. This 0.654-inch group was the largest of this test.
JSBs made a 10-shot group that measured 0.569 inches between centers. This group was also horizontal in shape.
JSB Jumbos opened up a bit on setting 5, as well. These measure 0.569 inches between centers.
Finally, the power was dialed up to 10, and 10 Premiers were fired again. This time the group shrank to 0.329 inches. I call that a significant result; because not only is this group much smaller than the group fired on power setting 6 with the same pellet, it’s also very round and uniform. I think it shows that the factory barrel likes this pellet at power setting 10.
On power setting 10, 10 Premiers made this nice round 0.329-inch group at 25 yards.
And JSB Jumbos at power setting 10 produced a group measuring 0.359vinches. That’s just slightly larger than the Premiers. I think the rifle really likes power setting 10. This group isn’t as round, but it’s clover-shaped, which is also good.
Ten JSB Jumbos went into 0.359 inches at 25 yards.
Interpretation of these results
I will hold off interpreting the results of all the testing until I’ve shot the 1:22 barrel at 10 meters and 25 yards, but something stands out in today’s test. At power setting 6 and 25 yards, accuracy went out the window. It got better at the low end of the scale and again at the high end; but for both pellets, power setting 6 didn’t seem to work well at 25 yards. Yet, at 10 meters, that setting and JSB pellets produced the tightest group of the entire test.
This is the kind of thing an owner has to do with his rifle with each pellet he plans to shoot. And it’s also why spending an inordinate amount of time examining one specific power setting is useless if you don’t know the big picture first. Look at the JSB target on the zero setting at 10 meters to see what I’m saying.
How does rifling twist rate affect velocity and/or accuracy? Part 5
by Tom Gaylord, a.k.a. B.B. Pelletier
If you’ve reached this webpage because you’re searching for information about the AirForce Talon SS rifle in .22 caliber, please note, this report is not about a standard rifle. You may be more interested in the 10-part Talon SS test than in this one.
For those who are following this series, this is the first accuracy test. Today, I’ll test the barrel made by Dennis Quackenbush with a twist rate of 1:12 inches. I’m testing with two pellets at this time — the 14.3-grain Crosman Premier and the 15.9-grain JSB Exact. You’ll soon see why I’ve chosen to test with just two pellets, as there are several variables that each required testing. I’m trying to limit the number of shots in each test.
Following today’s test, I’ll do the same thing with the factory barrel and also with the other barrel Quackenbush made with a 1:22 inch twist rate. Then, I’ll write a report that analyzes the data from the three accuracy tests. After that, I plan to shoot each barrel at 50 yards for accuracy, but that will probably be done on power setting 10, alone, unless there are compelling reasons to do otherwise.
The test
I shot the rifle at two distances — 10 meters (11 yards) and 25 yards. Each pellet was tested on each power level — zero, 6 and 10. If you forget how those levels are controlled, you can find them described and shown in Part 2. The standard was a 10-shot group. Because the Talon SS is so easy to shoot (it requires no special holding technique), I went with just one group. There’s always the possibility of returning and shooting additional groups after everything has been tested; but as we’ve learned from reading this blog, a 10-shot group is very representative of the true accuracy of a rifle.
There were no called fliers in this test. While that sounds incredible for 120 aimed shots (yes, 120 shots!), I was resting the rifle in the groove of a large sandbag while shooting and it was extremely stable. I did note on one test of the rifle at zero power immediately after filling the reservoir that the pellets were stringing wildly (about 6 inches) in the vertical dimension. I threw that test out and shot another group with the same pellet after the reservoir pressure had dropped a bit. That one seemed reasonable.
I shot 20 shots on zero power (10 with each pellet) and 20 shots on power level 6. The reservoir was refilled before I shot 20 shots on power setting 10 with both pellets. I did this at 10 meters and again at 25 yards. I have some things I want to say about this test. Before I do, let’s look at the results.
Ten-meter testing
At 10 meters, the first test was with both pellets on power setting zero. Before I tested the gun, the rifle was zeroed so the pellets would land close to or inside the bull I was aiming at, but not hitting the center — as that was the aim point for every shot. As always, it’s the group size I’m concerned about — not where the pellets land.
Zero power
Premiers made a 10-shot group that measured 0.509 inches between centers. Though the group is large for a Talon SS, in my experience, it’s fairly well distributed. So, the barrel made by Quackenbush seems to be accurate enough for this test. We know from the velocity test that Premiers average 452 f.p.s. in the 1:12 barrel and the velocity spread is 56 f.p.s.
Ten JSB Exacts made a group that measures 0.578 inches between centers. That’s just a little larger than the Premier group. It’s also a bit more horizontal than vertical. We know from velocity testing that this pellet averages 434 f.p.s. in the 1:12 barrel, with a spread of 56 f.p.s.
On zero power, 10 Premiers made a 0.509-inch group at 10 meters in the 1:12 barrel.
On zero power, 10 JSBs made a 0.578-inch group at 10 meters in the 1:12 barrel.
Power setting 6
Moving up to power level 6, I fired one shot to see where the pellet was going and to allow the valve to adjust to the new setting. Ten Premier pellets made a group measuring 0.408 inches between centers. Velocity at this power setting averages 777 f.p.s. in the 1:12 barrel, with a spread of 63 f.p.s.
Ten JSB pellets made a group that measured 0.419 inches between centers. It was really too close to the other group (of Premiers) to make a distinction; but when I measured it, that’s what I got. The average velocity on this setting with the JSB pellet is an average 786 f.p.s., with a 41 f.p.s. spread.
On power setting 6, 10 Premiers made a 0.408-inch group at 10 meters in the 1:12 barrel.
On power setting 6, 10 JSBs made a 0.419-inch group at 10 meters in the 1:12 barrel.
Power setting 10
Moving up to power setting 10, I fired one shot to set the valve. Then, 10 Premiers made a 0.281-inch group. The velocity at this power setting averages 846 f.p.s., with a spread of 16 f.p.s.
Ten JSB pellets made a group that measured 0.286 inches between centers. Once again, the difference between the JSBs and Premiers was really too close to call. At this power setting, the velocity averages 830 f.p.s., with a spread of 15 f.p.s.
On power setting 10, 10 Premiers made a 0.281-inch group at 10 meters in the 1:12 barrel.
On power setting 10, 10 JSBs made a 0.286-inch group at 10 meters in the 1:12 barrel.
That concludes testing at 10 meters. Now, it’s time to pull back to 25 yards and try everything all over.
Twenty-five-yard testing
Starting at zero power, this was where I discovered that I had to throw out the first group for extreme vertical stringing. After that, though, the gun calmed down and seemed to group as well as it could.
Zero power
On zero power at 25 yards, Premiers made a 10-shot group that measured 0.903 inches between centers. This is a larger group than I’m used to with an SS, but it seems to be more due to the valve and the velocity variation than the barrel. You’ll notice that there’s a smaller group of 6 shots at the bottom of this group. They were not fired sequentially, though.
Ten JSB Exacts made a group that measures 1.142 inches between centers. Again, there was a smaller group within the large group, but it contains fewer shots than the small group within the Premier target.
On zero power, 10 Premiers made a 0.903-inch group at 25 yards in the 1:12 barrel.
On zero power, 10 JSBs made a 1.142-inch group at 25 yards in the 1:12 barrel.
Power setting 6
Moving up to power level 6, I fired one shot to see where the pellet was going, plus to allow the valve to adjust to the new setting. Ten Premier pellets made a group measuring 0.375 inches between centers. Velocity at this power setting averages 777 f.p.s. in the 1:12 barrel, with a spread of 63 f.p.s.
Ten JSB pellets made a group that measured 0.979 inches between centers. The average velocity on this setting with the JSB pellet is 786 f.p.s., with a 41 f.p.s. spread. That’s quite a difference from the Premier group at the same power setting/same distance.
On power setting 6, 10 Premiers made a 0.375-inch group at 25 yards in the 1:12 barrel.
On power setting 6, 10 JSBs made a 0.979-inch group at 25 yards in the 1:12 barrel.
Power setting 10
Moving up to power setting 10, I fired one shot to set the valve. Then, 10 Premiers made a 0.753-inch group. It’s still a fairly well-rounded group.
Ten JSB pellets made a group that measured 0.944 inches between centers on power setting 10. This time, the group was not just larger, there were several pellets that did not land in the same place. It’s also strung out horizontally.
On power setting 10, 10 Premiers made a 0.753-inch group at 25 yards in the 1:12 barrel.
On power setting 10, 10 JSBs made a 0.944-inch group at 25 yards in the 1:12 barrel.
What did we learn?
This is just the first test of 3 barrels, so it’s too early to draw a lot of conclusions. But there are things that can be said about this one test. For starters, JSB Exact pellets seem to spread out at the longer distances and higher power levels. Are they over-stabilizing? Too soon to tell, but the Premiers definitely out-grouped them. That may change when we test the factory barrel.
Premiers really only opened up at 25 yards on power setting 10. And they didn’t group well at 10 meters on zero power. Everything else was okay. Are they a more stable pellet? In the 1:12 twist barrel, they seem to be.
In researching this report, I’ve read in several places where gun writers say there is no problem with over-stabilization from fast twist rates. They say that as long as the bullet is stable, there’s no difference in accuracy, regardless of the twist rate. That may or may not be true for bullets (though I doubt that it is), but it certainly isn’t true for these two pellets! That much has been proven pretty clearly.
Beyond that, I don’t think I can say anything else. Next, I’ll test the factory barrel.
This test involves shooting 12 10-shot groups per barrel, so it’s very involved. That’s why I can’t do all three barrels at one time. I hope you understand that.
How does rifling affect velocity and/or accuracy? Part 4
by Tom Gaylord, a.k.a. B.B. Pelletier
Announcement: Bill Cardill is this week’s winner of Pyramyd Air’s Big Shot of the Week on their airgun facebook page. He’ll receive a $50 Pyramyd Air gift card. Congratulations!
Bill Cardill is the Big Shot of the Week on Pyramyd Air’s facebook page.
This could also be called the Twist-Rate Test. It’s a look at how different rifling twist rates affect both velocity and accuracy. The standard smallbore airgun twist rate has been one turn in 16 inches for all 4 calibers since the beginning of modern rifled airguns in 1905, and there’s been no published test that looked at any other rate. So, this is a first look at how different twist rates can affect an airgun pellet in flight.
I’ve selected an AirForce Talon SS rifle in .22 caliber as a testbed because changing the barrels is a 5-minute operation. I’m able to shoot every pellet in each barrel using the same basic powerplant. Because the Talon SS has adjustable power, I can adjust the power to different levels for each barrel and pellet and keep the test conditions constant.
A quick look
Today’s report is a summary of what’s been learned so far. I’ve tested the factory barrel and two experimental barrels with different twist rates. The test has been at three different power levels with two different pellets. While that all sounds simple, it gets complex quite fast; and this report is needed to put things into perspective for everyone.
I will not talk about percentages, nor will I show graphs that overlay one barrel against the others because, frankly, I haven’t done enough testing to support such a presentation. In the world of testing, what I’ve done is called a quick look — which means I ran a small test just to see how the data would play out. Any gross trends should be visible, but a lot of the data will remain hidden until more tests are done.
Proof of concept
The easy way to think of this is to think like an experimenter who wants to find out how well something works. Let’s take Melvin Johnson, the inventor of the model 1941 Johnson Automatic Rifle. He had an idea that he wasn’t sure would work, so he spent $300 of his own (borrowed) money to have a machine shop build a testbed. It wasn’t a gun — it was just an action and barrel. He tied it down and fired it from several feet away with a lanyard. All it did was show him that the idea was sound and workable. Today, this is called a proof-of-concept model.
And that’s what our two test barrels are — proof-of-concept barrels. They’ll tell us generally what the two non-standard twist rates (1:12″ and 1:22″) do relative to the factory Lothar Walther barrel that has a 1:16″ twist rate. If the results are wildly different, then we’ll know what direction our next tests should take. But we didn’t get wildly different test results. Let’s see what happened and speculate on what it means.
Two pellets and three power settings
I shot each pellet at three different power settings in each barrel. Before I get into a discussion of how things went, I want to caution you that every time I run this test the numbers are going to be different. You might think if that’s the case then why test at all. Well, although the numbers are different, they are still very close to each other.
So, we’re NOT looking for absolutes in this test. We’re looking for gross TRENDS. And I think we found some!
Fact 1. At power setting zero, the slower twist rate (1:22″) gives faster velocity
This is true for both pellets. As the twist rate slowed down (going from a fast 1:12″ to a slow 1:22″ rate), the average velocity increased EVERY TIME. Premiers went from an average 452 f.p.s. to 534 f.p.s. as the twist rate slowed down. JSB Exact 15.9-grain domes went from an average 434 f.p.s. to an average 521 f.p.s. But the factory barrel generally had the better velocity spreads. Not in all cases, but in most of them. While the factory twist rate is not as fast as a 1:22″ twist on power setting zero, it’s more stable.
This tells us that the faster twist rate does cause the pellet to slow down, as many people predicted. They often call it frictional loss, and I suppose that’s as good an explanation as any.
The other thing I want to say is that the Talon SS isn’t as stable at zero power as it is at higher levels. It wasn’t designed to be run at zero power, even though it is possible. The thinking is that if shooters are running at zero power they are either plinking ot shooting at targets that are very close. Either way, velocity stability doesn’t matter as much as it does on the higher power levels.
Fact 2. The slow twist (1:22″) barrel got to its top velocity earlier than any other barrel
On power setting 6, the slow twist barrel was shooting Premiers at an average 840 f.p.s. The factory barrel was at 818 f.p.s., and the 1:12″ barrel averaged 777 f.p.s. at the same power setting. At their top velocities (only on this test, remember), both other barrels hit just 846 f.p.s. (1:12″) and 849 f.p.s. (factory). The 1:22″ barrel went up to 854 f.p.s.
The same thing happened with the JSB Exact 15.9-grain dome, only the velocities were slower than with the Premiers.
What this tells us is the same thing the first fact told us: As the twist rate slows down, the rifle becomes more efficient.
And that would suggest several things. First and most important, that a slower twist rate will conserve air when all other things remain the same. The fact that I can get nearly the top velocity on power setting 6 means I can get a few extra shots per fill when using the slow-twist barrel.
The second thing is less important, but a slower twist rate will make it possible to achieve higher velocities. The difference, however, is so slight as to be insignificant. Compare 854 f.p.s. — the highest average velocity obtained on power setting 10 (from the 1:22″ barrel) with 846 f.p.s. — with the lowest average velocity obtained on power setting 10 (from the 1:10″ barrel). The difference isn’t worth the effort of getting a special barrel made since the factory barrel gives an average of 849 f.p.s. on setting 10.
Fact 3. The rifle gets the tightest velocity spreads at the highest power setting
This is generally true with all three barrels tested, though there was one anomaly. The 1:22″ barrel did have a tighter velocity spread on setting 6 than on setting 10 when the Premier pellet was tested. But the difference is only 3 f.p.s., and might just as easily have been reversed in a second test.
But the general trend for the velocity spread to tighten as the power is increased held for all three barrels and is probably a trend that will repeat with other pellets and at other power settings.
This trend doesn’t tell us as much about the barrels as it does about the rifle. It indicates that the Talon SS becomes more stable at the higher power settings — regardless of the twist rate. It does, however, make the next fact stand out.
Fact 4. The 1:22″ barrel produced similar power on setting 6 as on setting 10 with JSB pellets
This is the biggest discovery these tests have revealed. On power setting 6, the 15.9-grain JSB Exact domes averaged 817 f.p.s., while on power setting 10 they averaged 815 f.p.s. The velocity spreads for this pellet were 14 f.p.s. on setting 6 and 10 f.p.s. on setting 10. In essence, the power was at its maximum on power setting 6 with this pellet.
With the Premier pellet, the velocity was 840 on setting 6 and 854 on setting 10. And the spreads were 16 f.p.s. and 19 f.p.s., respectively.
So, the Talon SS develops its maximum power with these two pellets around power setting 6 when the 1:22″ barrel is used.
What does it all mean?
Given these gross trends, what can we take away from the testing that has been done to this point — if anything? I think it’s obvious that the gun is more efficient when the 1:22″ barrel is installed. However, I also want to note that all three barrels converged at power setting 10. None of the barrels were superior, as long as that power setting was used. But on power setting 6, the 1:22″ barrel is superior from the standpoint of velocity, alone.
If I can operate the Talon SS on power setting 6 and get max power, then I can probably get a couple more shots per fill of air before the gun falls off the pressure curve. Of course, that’s only speculation until I test it.
But what interests me now is how the rifle will perform on targets with the three barrels. In other words, is there a noticeable accuracy difference with one of the barrels over the other two? Or, conversely, is one of the barrels noticeably less accurate than the other two?
If the 1:22″ barrel were also more accurate than the factory barrel and the 1:12″ barrel, then we would have a great finding. I would also need to test the rifle with heavier and lighter pellets, to see if the trend continued. Or, is the factory barrel with its 1:16″ twist rate the best all-around compromise?
As I said in the beginning of this report, this is a huge test, and one that has never been published before. The goal is to learn more about how the rifling twist rate affects the performance of the pellet. I’m hoping that these trends we see today will continue as the testing continues, and we will at some point be able to make some educated assumptions about airgun barrel twist rates and their association with performance.
How does rifling twist rate affect velocity and/or accuracy? Part 2
by Tom Gaylord, a.k.a. B.B. Pelletier
Let’s begin our look at the effects of the rifling twist rate on accuracy and velocity. This will be a huge test. I know many of you will want to know THE ANSWER sooner than I get to it. All I can do is ask you to be patient because this has never been documented for the public, if indeed, it has even been done before.
We’re testing the 1:22″ twist barrel that Dennis Quackenbush made for the Talon SS test rifle. I’ll use the velocity figures that I recorded for the factory barrel several months ago in the 10-part Talon SS report. After I’ve tested the 1:10″ twist barrel (in the next report), I’ll also retest the factory barrel following the exact test structure I’m using for both Quackenbush barrels. I know my rifle very well and don’t expect the numbers to be that far off. So, you can accept today’s figures as gospel, but I’ll retest the gun just to make sure.
I followed a fill process that’s very exacting, so each test is the same as all others. I’m not going to bore you with the minutiae, but I discovered while testing the gun on the lowest power setting that the velocity climbed after about 5 shots immediately after a fill, so I refilled the reservoir after each test on low power. On the higher powers, the gun is very stable across the useful fill, so those tests did not all begin at 3,000 psi. They were tested with 2,600 psi to 2,800 psi in the air reservoir — a range where the velocity is extremely regular.
I’m going to use only two pellets initially. Until I learn something about the performance of these barrels, it’s not worth spending endless time running down “facts” that don’t really matter. Later, if the data indicate a need for expanded testing, there will be additional velocity tests with other pellets.
The best way to view the results is when they’re grouped by power setting. Each pellet was tested with the rifle set at three different power settings. Since my gun doesn’t have a scale on the power adjustment window, I put a piece of tape there and marked it for the two higher power settings. The lowest setting is with the power screw indicator as far to the left as the window permits.
Tape marks the two higher power settings. When the screw head is centered on the index mark, the power is correct. When the screw head is as far to the left in the window as it will go, the power is on the lowest setting.
Power setting 0
Factory barrel
On zero power with the factory barrel, 14.3-grain Crosman Premier pellets averaged 486 f.p.s. the range was from 451 to 522 f.p.s. That is an average energy of 7.5 foot-pounds.
On zero power, 15.9-grain JSB Exact pellets averaged 507 f.p.s. The range went from 498 to 521 f.p.s. At the average velocity, this pellet produces 9.08 foot-pounds on this power setting. And the spread is 23 f.p.s.
The velocity spread for both pellets is on the high side, with Premiers being the highest at 71 f.p.s. That tells us the valve is not too stable at the lowest power level and a full fill of air.
1:22 barrel
On zero power with the 1:22 barrel, Crosman Premier pellets averaged 534 f.p.s. The spread went from 499 to 569 f.p.s. — a range of 70 f.p.s. At the average velocity, this pellet produces 9.08 foot-pounds of muzzle energy.
On zero power with the 1:22 barrel, the JSB Exact pellet averaged 521 f.p.s., with a range from 482 to 528 f.p.s. That’s a spread of 46 f.p.s. At the average velocity, this pellet generated 9.59 foot-pounds of energy.
Again, there was a high velocity spread for the Premier pellets, and the JSBs were tighter. With both pellets, the muzzle energy increased with the 1:22″ twist over the factory barrel.
Power setting 6
Factory barrel
On setting 6, the Crosman Premier pellets averaged 787 f.p.s. from the factory barrel. The range was from 775 to 800 f.p.s., so the spread was a tighter 25 f.p.s. At the average velocity, this pellet generated 19.67 foot-pounds of energy.
On the same setting, the JSB Exact pellets averaged 778 f.p.s. with the factory barrel. The range was from 769 to 785 f.p.s., so the spread was 16 f.p.s. At the average velocity, this pellet generated 20.57 foot-pounds of energy.
1:22 barrel
The Crosman Premier pellets averaged 840 f.p.s. from the 1:22 barrel on power setting 6. The range was from 831 to 847 f.p.s., so the spread was a much tighter 16 f.p.s. At the average velocity, this pellet generated 22.41 foot-pounds of energy.
On setting 6, the JSB Exact pellets averaged 817 f.p.s. from the 1:22 barrel. The spread went from 810 to 824 f.p.s. At the average velocity, the energy generated at the muzzle was 23.57 foot-pounds.
Power setting 6 boosted the power a lot. It also stabilized the velocity quite a bit with both pellets. As you can see, the 1:22″ barrel outperformed the factory barrel by quite a lot. This is especially noticeable when you look at the muzzle energy.
Power setting 10
Factory barrel
The Crosman Premier pellets averaged 854 f.p.s. from the factory barrel on power setting 10. The range was from 850 to 860 f.p.s., so the spread was a very tight 10 f.p.s. At the average velocity, this pellet generated 23.16 foot-pounds of energy.
On setting 10, the JSB Exact pellets averaged 823 f.p.s. with the factory barrel. The spread went from 821 to 825 f.p.s., which is just 4 f.p.s. At the average velocity, the energy generated at the muzzle was 23.92 foot-pounds.
1:22 barrel
Crosman Premier pellets averaged 854 f.p.s. from the 1:22 barrel on setting 10 — the identical speed they got with the factory barrel on this setting. The range was from 844 to 863 f.p.s. Although the average was the same as for the factory barrel, the spread was much greater at 19 f.p.s. At the average velocity, this pellet generated 23.16 foot-pounds of energy.
On setting 10, the JSB Exact pellets averaged 815 f.p.s. from the 1:22 barrel. That is LESS than it was on power setting 6. The spread went from 809 to 819 f.p.s. At the average velocity, the energy generated at the muzzle was 23.46 foot-pounds.
Power setting 10 is as high as I ever run my Talon SS. I haver determined that with a 12-inch barrel any setting above this one just wastes air. While the velocities may be a little different with the different twist rates, I believe the general rule will hold that setting 10 is as high as any 12-inch .22-caliber barrel wants to go — at least with the powerplant on my rifle.
The results of this test
As you can see from these results, the gun is wasting air on power setting 10 with the 1:22 twist rate. It is much more efficient on power setting 6. And it does not give up any power to the factory barrel, leading me to wonder if a 1:22″ twist rate might not be a better rate for .22-caliber pellets in the middle power range.
The factory barrel edged out the barrel with a slower twist by getting 23.92 foot-pounds of energy from JSB pellets on power setting 10 compared to 23.57 foot-pounds with the 1:22″ barrel shooting JSB pellets on power setting 6. I don’t know what that says, but there it is.
We’ve learned a little from this test, and we now know there’s so much more to be explored. The results were not as dramatic as some might have anticipated. Many thought the slower 1:22″ twist would have sped up the pellets noticeably, but that didn’t happen. What it did seem to do was make the rifle more efficient in the middle range of power.
It’ll be interesting to see what the 1:12″ barrel does under the same circumstances. After that, I’ll retest the factory barrel at these test settings to verify they’re correct.
How does rifling twist rate affect velocity and/or accuracy? Part 1
by Tom Gaylord, a.k.a. B.B. Pelletier
This is going to be a long report. How long, I can’t say at this time because I’m sure I don’t know everything we’re going to do. Many airgunners have wondered openly how the twist rate of the rifling affects how their guns shoot. But wonder is as far as it’s gone because I’m not aware of any test report that’s ever been written on this subject. Indeed, whenever we get on the subject of twist rates, the equations start flying and we all lean back in our easy chairs while we ponder the implications. But nobody ever seems to do anything concrete to answer the question. That ends today.
What is twist rate and what does it do?
First, let’s all understand what we’re talking about. As a pellet travels down the barrel of an airgun, it’s held by ridges called lands that run along the inside of the barrel. These lands stick up in the barrel and twist in a spiral, engraving the sides of the soft lead pellet and making it spiral as it moves forward. The twist rate is how far the pellet must travel in the bore to make one revolution. A 1-in-10-inch twist rate means that the pellet is turning one complete revolution for each 10 inches of barrel it traverses. That twist rate is written as a ratio — 1:10 inches.
Spinning helps stabilize a pellet in flight. Just as a bullet is made stable by spinning on its axis like a top, a pellet is also stabilized the same way. But pellets of the diabolo design (hollow tail and wasp waist) are also stabilized by the high drag of their tails and the forward weight bias of their design (i.e., more weight in the head than the tail). So, spin is just one of the things that helps stabilize a diabolo pellet in flight, and exactly how much spin it takes is the question we’re discussing. We also want to know what the other effects of the spin rate might be. For instance, does a faster spin slow down the pellet because of greater friction while it’s inside the barrel?
The most common twist rate
When pellet guns were first rifled, they were given the twist rate that was common for the .22 long rifle cartridge at that time, which is one complete turn in 16 inches of travel in the barrel (written as 1:16″). If there was any experimentation with other rates, nothing’s been written about it; so, the pellet gun twist rate has been 1:16″ since the beginning — about 1905. That holds true for all four smallbore calibers (.177, .20, .22 and .25).
I can’t say for certain if other twist rates have ever been used. I hear reports of other rates, such as 1:14 inches, but no proof is ever offered. My thought is that perhaps these other rates are obtained from people incorrectly measuring the twist rate. The simplest way of measuring the twist rate in any rifled gun is to make a mark on a cleaning rod, then pass a wire brush down the bore of the gun on the end of that rod and note how far it goes before the rod makes one complete turn. This method is makeshift, to be sure, but it’s accurate enough for a rough estimate.
I don’t doubt that other twist rates have been used at times, but the makers of those barrels have not made a point of mentioning it in their promotional literature. Twist rate is something airgun writers have elected to ignore over the years, perhaps not finding the subject worth discussion since all airguns seem to have the same rate.
A few of us, though, have wondered what might happen if the twist rate was changed. Since the only way to tell is to test barrels with different twist rates in the same gun, and since nobody makes barrels of different twist rate for airguns, the question has remained unexplored until now. Some time ago, airgun maker Dennis Quackenbush approached me and asked if I would be interested in conducting such a test. I said yes, and we both settled on the Talon SS from AirForce Airguns as the ideal testbed because the barrels can be exchanged so easily.
The experiment
Dennis made two barrels for my Talon SS. Both are .22 caliber, which is also the caliber of the factory Lothar Walther barrel in my gun. He made these barrels from scratch. They’re cut-rifled, which means that each groove is individually cut. Doing it that way, he was able to use a sine bar (a tool used to measure angles) to control the rifling pitch that results in the twist rate.
Talon SS factory barrel (center) is flanked by the two barrels made by Dennis Quackenbush for this test.
Dennis marked each barrel with the twist rate. The top is 1:12 inches and the bottom is 1:22 inches.
Dennis crowned his barrels the same way Lothar Walther crowned theirs.
One barrel he made had a 1:22″ twist rate. That happens to be the twist rate of the .22 short cartridge when a rifle is chambered for that cartridge, alone. The .22 short bullet weighs 29 grains, nominally. If the rifle is chambered for long rifle cartridges, as well, then the 1:16″ twist is used because the longer, heavier 40-grain bullet requires a faster spin.
In the other barrel, he put a 1:12″ twist. That was for no reason other than it’s far enough from 1:16″ and 1:22″ twist rates that there ought to be some differences that can be observed. One curious sidenote to this test is the fact that Aguila makes a special subsonic .22 long rifle cartridge that has a 60-grain bullet. To stabilize that bullet that leaves the muzzle at around 900 f.p.s., a rifle has to have a 1:10″ twist rate. There are special barrels made for the Ruger 10/22 rifle for just that round. Like the Talon SS, the 10/22 has a barrel that’s quick and easy to change.
The most common method of rifling barrels these days is button rifling, in which a hardened “button” is either pushed or pulled through the bore, cutting all the grooves at the same time (actually, it doesn’t cut the metal so much as it “irons” the steel into the desired shape). The button must be made for a single twist rate, taking into account the thickness of the barrel walls and the type of steel in the barrel because the steel springs back a little after the button has passed through. So, the spring rate of the barrel steel must be controlled by the size and shape of the button, as well as the type and thickness of barrel steel, itself. Using a button is a very fast way to rifle many barrels, but it limits you to just one twist rate per button.
Cut rifling is therefore a slower process but does give the barrel maker more flexibility over the type of barrel he makes. Dennis didn’t put a choke into his barrels because we aren’t interested in their ultimate accuracy. But the factory Lothar Walther barrel is choked. So, this will not be a test that pits the accuracy of the Quackenbush barrels against the Lothar Walther barrel. We’ll be examining accuracy potential, but only so far as one twist rate seems to have an advantage over the other with a given pellet at the same power setting. If something interesting pops up, we may wish to explore it further with other barrels in the future.
AirForce helped, too
Dennis contacted John McCaslin of AirForce Airguns for some of the critical dimensions of the barrels. John shared these with him and also provided the bushings for the barrels he made. Even though they were made 12 years after my SS was made, these bushings fit my rifle perfectly.
Test objective 1
The first test objective is to determine the effect of a different rifling twist rate on the accuracy of various pellets at various velocities with barrels of different twist rates. All three barrels will be considered, but we’re really interested in the results of the two barrels supplied by Quackenbush. I can’t say that the factory barrel will be used as a control because it’s made differently than the two barrels Dennis has made (different rifling method and it’s choked). But the data will be included in the test report simply because it exists and may be of interest at some point. Any poential accuracy differences will be noted.
I’ll conduct this test at 25 yards and again at 50 yards. That will tell us how the different twist rates perform at different distances.
Test objective 2
Another factor that airgunners have talked about for a long time is the effect of twist rate on velocity. This discussion has been limited to big bore airguns because, as I’ve noted, all smallbores have the same twist rate. The popular theory is that a faster twist rate will result in a slower bullet velocity when everything else is the same. I’ll test the barrels at different power settings for each pellet I test.
What we’ll get from this test is a broad look at how the twist rate of a rifled barrel impacts (or doesn’t impact) the overall performance of pellets in a gun whose baseline performance we already know very well. I’ve thought long and hard about what would be the best way to conduct the test. Do I test the velocity first and then the accuracy? Or do I turn it around and test accuracy before velocity? I have a plan in mind, but I’d like your input before I start the testing. Remember that I already have a lot of good data on this rifle using the factory barrel.
Summary
As far as I know, an experiment like this has never been published before. Perhaps it’s been done, or perhaps parts of it have been done. If so, they didn’t put it in print. Neither Dennis nor I know how this will turn out. As he says, we’re pushing back the boundaries of ignorance in airguns.
I’d like to thank Dennis Quackenbush in advance for the work he’s done to make this test possible. I also want to thank AirForce Airguns for their part in what we’re about to do.
