Posts Tagged ‘aim point’
FWB 300S vintage target air rifle: Part 5
by B.B. Pelletier
The FWB 300S is considered the gold standard of vintage target air rifles.
This is a test I said I would do the next time I got a calm wind day at the range. That day came last Friday, and I took the opportunity to test the FWB 300S at 50 yards with a scope. This test was designed to see if there is any discernible accuracy difference between pellets that are sorted by weight and those selected at random from the tin. If you read part 4, you’ll see that I was surprised to find that these JSB Exact RS pellets I selected for their accuracy had such a variation in weight. I sorted through almost 40 pellets to find 20 that weighed exactly 7.3 grains. Though the weight difference was only four tenths of a grain, it was more than expected and more pellets were affected than I thought.
The JSB Exact RS pellet was chosen because of previous performance demonstrated in part 3. And I had to choose a domed pellet because out at 50 yards no wadcutter can possibly be accurate — I’ve proven that on many occasions in the past.
In part 4, I tested the rifle at 50 yards using the target sights that come on it, and I got two groups of 10 shots each. One was with random pellets taken from the tin. That group measured 1.689 inches between the centers of the two widest shots, while the other was 10 weight-sorted pellets that grouped in 1.363 inches. I didn’t feel that test was conclusive, so I wanted to return with the rifle scoped to see what it could do.
Not only did I mount a scope on the rifle, I also installed a scope level, and on every shot the bubble was leveled. That eliminated the possibility of any cant, so the rifle was always shooting in the same orientation.
The scope hangs over three-quarters of the loading port, making loading a chore. Notice how close together the scope rings are, yet they occupy the entire length of the dovetails. The 300S is not made for a scope! Notice, also, the scope level that was consulted on every shot.
I mounted a Leapers 3-9×50 scope with AO. It’s an older version of the one I linked to, but the specs are mostly the same. Notice in the photo that this scope was almost too long for the rifle, even though it was mounted at the extreme rear of the spring tube.
Where I had used a 3-inch bull target with the aperture target sights, I switched to the smaller 10-meter target when using the scope. The pellets were falling off the target paper anyway and onto the plain backer paper attached to the target frame, because of the large drop of this pellet at 150 feet.
Perfect day
I couldn’t have asked for a better day in which to shoot. Since I was at the range very early, there was absolutely no breeze. The sun hadn’t risen very high, so I didn’t need to shield my non-sighting eye. The rifle rested in the bunny bag dead calm, so altogether this was as perfect a test as I could have run.
Bore already seasoned
Because the bore had been shooting JSB Exact RS pellets last, it was already seasoned for this test. Still, I did shoot the rifle a few times to wake up the action. Then, I began the first group of unsorted pellets.
This time, the pellets did very poorly — grouping 10 shots into 3.152 inches at 50 yards. The group is very elongated, looking like a large velocity swing. The group measures just 1.178 inches wide, which is less than half the height.
Ten unsorted JSB Exact RS pellets strung out vertically at 50 yards. The rifle shot much better with target sights! Should I have warmed the gun more?
Next, I shot the pellets that were sorted by weight. Ten went into a group measuring 1.606 inches across. This group is fairly round and well-distributed, so it makes me wonder all the more about the first group. Perhaps the gun needed longer to warm up for the first group than I allowed?
This group of 10 weight-sorted RS pellets is much rounder, but it’s no better than the best group shot with target sights.
Test is not conclusive
I’m declaring this entire test invalid. I think I’ve stretched the FWB 300S beyond its capability, and the results are not telling me what I need to know. I’m aware that others have shot 10-meter rifle at 50 yards and say they’ve gotten good results, but clearly I’ve not been able to do the same with this rifle.
I think the test itself is worth pursuing, but with a rifle better-suited to accuracy at 50 yards. Pushing the FWB 300S outside its comfort zone was not a good idea. But I have several accurate air rifles that are all capable of grouping well at 50 yards. That’s what I need to rerun the test.
FWB 300S vintage target air rifle: Part 4
by B.B. Pelletier
The FWB 300S is considered the gold standard of vintage target air rifles.
Before we start, a word about some of the airguns shows that are coming up. First there is this:
Pacific Airgun Expo
March 10 & 11, 2012
Placer County Fairgrounds
Roseville, CA (just NE of Sacramento on Hwy 80)
Contact Jon Brooks Don Reed (corrected 3/6/12)
Call 916-564-5225 (corrected 3/6/12)
LASSO big bore shoot
March 17, 2012
Terry Tate’s farm
Near Sulphur Springs, TX
This one isn’t well advertised.
Flag City Toys That Shoot
April 14, 2012
Lighthouse Banquet Facility
10055 S. R. 224 West
Findlay, OH 45840
Contact Dan Lerma, 419-422-9121
or artnron1@juno.com
NRA Annual Meetings
April 13-15, 2012
St. Louis, MO
This is like a mini SHOT Show that’s open to the public. It has a 10-meter airgun range (run by Pyramyd Air) for shooting manufacturer-supplied airguns (there’s a charge for shooting). Free to NRA members, $10 for non-members. Click for website. Pyramyd Air is giving away free tickets to the show. If you’re not an NRA member and want to get in for free, read the announcement on their facebook page and follow the directions.
Airgun Extravaganza
April 27-28, 2012
Malvern, AR 72104-2005
Contact Seth Rowland, 501-276-1535 or seth.rowland@att.net
Seth is still accepting table reservations, so contact him if you want to reserve a sales or display table.
Okay, on to today’s report.
I didn’t think this day would come so soon, but I’m going to show you what happens when you shoot the FWB 300S at 50 yards. Or more correctly…when I shoot it! I say that because 50 yards is a distance at which all false pretense of accuracy falls away. Fifty yards is a harsh challenge for a 650 f.p.s. air rifle like the 300S. All the wonder of those tiny groups at 10 meters becomes doubt that you can even shoot this far when the range stretches out more than four times as far.
I needed a windless day and as luck would have it, I got one. Or at least one where what little breeze there was could easily be managed. When I got set up to shoot, it was about 8:15 a.m., and the breeze was running from still to an occasional puff of about 1 m.p.h.
I used the sandbag rather than the rifle rest because I already knew the 300S did well on it. I first fired about four rounds to warm the action and to “awaken” the mechanical parts. I’ll talk a lot more about that in a PCP primer I’m writing, but even spring-piston guns have to wake up if they’ve sat for more than a couple hours.
I’m shooting the JSB Exact RS pellet for this test. We all agreed that to test the gun with wadcutters at this range would be unfair, because wadcutters are known to be inaccurate after about 25 yards. And the RS pellets proved to be the most accurate domed pellets in the accuracy test I did.
For targets, I wanted to use the 50-foot timed and rapid-fire pistol targets that I always use at 50 yards. The bull measures just larger than 3 inches, which is a good size for most peep sights at 50 yards. I like these targets also because they measure 10.5″x12″, which gives a lot of room for the pellets to miss the mark and still be seen. I knew the pellets would drop when going 50 yards, and I’d planned to stack two targets — one above the other, so I could aim at the top bull and possibly hit somewhere on the target below. But I only had two of these targets! I’d failed to pack enough of the right kind of targets in the range box. Though I had plenty of targets, only two were what I wanted.
No problem, I thought. Years ago, I figured if this ever happened I would use 10-meter pistol targets instead of these larger targets. They’re on smaller paper, but I could still place one above each larger target to use as an aim point. Ten-meter pistol targets have a bull that measures 2.35 inches across. It looks similar to the larger bulls when you look at them casually, but at 50 yards the difference through the sights is noticeable. They’re too small in the front aperture, which leads to possible aiming errors. I could see that on the first group I fired and also when I examined the group afterwards.
The first target suffered from an aim point that was too small for precision. It measures 2.407 inches between the centers of the two holes farthest apart.
As I predicted, the group dropped about eight inches at 50 yards, so the group was printed on the target below the one I aimed at. I knew that the smaller bull was too small to work well at this distance. But there was another way of doing this.
I still had two of the 50-foot timed and rapid-fire targets stapled to the target backer; and underneath everything, I’d stapled a 2′x4′ sheet of plain target paper. It’s the back of a silhouette target that I always use when I’m unsure of where my bullets or pellets will go. The plain light paper allows me to see the holes even though they don’t strike the intended target. Because it’s so large, it covers the entire target backer; so, unless the rifle is really out of whack, I’ll see where the pellets are going.
Then, I proceeded to shoot another 10-shot group of unsorted pellets at the larger bull on the left, knowing that they would strike the plain target paper below this target. They landed about two inches below the target and gave me a perfect group of 10 on the plain paper.
This time, the bull was filling the front aperture as it should, so the group was much better. It measures 1.689 inches between centers. Remember, this is a 10-shot group. It’s about 40 percent larger than a 5-shot group fired under similar conditions. That doesn’t mean that it’s exactly 40 percent larger; and, yes, it’s possible for the first 5 shots to land the farthest apart, so that a 10-shot group doesn’t grow any larger. But the probability that you’ll do that is very low. If you keep on shooting after 5 shots, it’s more likely that your group will continue to enlarge until it’s, perhaps, 40 percent larger after 10 shots than it was after the first 5.
Ten-shot group at 50 yards with unsorted pellets. Ten shots made a 1.689-inch group. Nine of the shots went into 1.015 inches. The larger aim point helped reduce the group size.
Some notes on sorting the pellets
I had sorted the JSB pellets the evening before going to the range. Because JSB pellets are so accurate, I thought they’d also be very uniform, but they weren’t. To get 20 pellets that all weighed 7.30 grains, I had to sort through almost 40 pellets! The weight ranged from 7.10 grains to 7.40 grains. While that isn’t as large a spread as other pellets, it was still a surprise. I thought I might find two or three pellets that didn’t weigh the same, but it was worse than that.
By this time it was around 9 o’clock, and the breeze was picking up. I had to wait for breezes of 3 m.p.h. to die before shooting. When they did die, though, the air was perfectly still again. This time, 10 pellets that were sorted by weight grouped in 1.383 inches. That isn’t much better than the unsorted pellets, and it was not the result I’d expected.
Ten-shot group of weight-sorted pellets at 50 yards made this 1.383-inch group. Not much improvement over the unsorted pellets! You can see a very small 5-shot group at the left of the larger group. That group measures 0.577 inches between centers, but I can’t say that it indicates anything.
What happened?
This test didn’t turn out as I’d expected. Either the weight of the pellets doesn’t matter that much, or something else was happening to skew the results. I think I may know what that something is. It was apparent as I shot that I was unable to detect any slight canting of the rifle. There’s no bubble level on this rifle. And look at all three targets. They’re all wider than they are tall, which is a giveaway that I was canting the rifle randomly. In fact, this is such a telling result that I believe I have to rerun this test, just to eliminate the cant!
I’ve conducted a host of special cant tests in the past to learn about the effects of canting the rifle; plus, when I shoot my Ballard rifle — which has a bubble level attached to the front sight, it’s always difficult to center the bubble because it’s so sensitive. So, canting is a known problem with which I have some experience.
By the time I completed the group of weight-sorted pellets, the breeze had picked up and the day of testing this pellet rifle at 50 yards was over. But like I said, I’m not satisfied with these results and will have to run the test again. Next time, I’ll mount a scope, just for the additional precision it will give, plus it’s lot easier to use a bubble level with a scope than with a peep sight.
FWB 300S vintage target air rifle: Part 3
by B.B. Pelletier
Announcement: Shivashankar Raghu is this week’s winner of Pyramyd Air’s Big Shot of the Week on their facebook page. He’ll receive a $50 Pyramyd Air gift card! Congratulations!
Shivashankar says this is his 4-year-old son with his dad’s Diana Model 23 on the boy’s first day at their club!
The FWB 300S is considered the gold standard of vintage target air rifles.
We’ll look at accuracy today, but this isn’t our last look at the 300S. You convinced me to take this rifle to the range and test it at 50 yards. I’ll do that, but I have to have a perfectly calm day for it. Kevin also convinced me to test weight-sorted pellets against pellets straight from the tin, so that’s how I’ll do the test. I want to use domed pellets at that distance, so today I’ll be looking for a good one that the rifle likes.
More 300S trivia
Mac sent a batch of photos to show some details that few people have ever seen. I’ll show a couple today and more in the next report.
Remember the Running Target rifle we talked about last time? Well Mac sent photos to show how the loading port differs from the one found on the standard 300S match rifle. The port is the same size, but FWB has rotated it to the right to make access for loading a little easier. I guess they expected a lot of right-handed RT shooters, or more likely they also built one in a left-hand version. Mac’s is the right-hand rifle.
The standard 300S loading port is centered on top of the spring tube, to be equally accessible from either side.
On the right-hand Running Target rifle, the loading port is rotated to the right for better access from that side.
Accuracy
All of today’s shooting was done from a rest at 10 meters. I attached the Gehmann color filter wheel to the rear aperture and used the yellow filter to sharpen the bulls. It seemed to work okay. Unless I were to use it for a lot longer, I really could not say that it adds anything. I don’t shoot a 10-meter rifle often enough to notice things like that.
Pellet head size is important when shooting a target rifle, and I shot pellets with heads of 4.50mm and 4.52mm, but none with a 4.51mm. Interestingly, the 4.50mm heads ranged from bad to good; so even when you have a single head size, you aren’t done looking for the right pellet.
Pellets that didn’t make the grade
I tried nine pellets in this test. Seven were wadcutters and two were domes. RWS Hobby pellets and Gamo Match were the two that didn’t cut it. Both shot so poorly that I didn’t waste any time with them. Oddly, in the test of the FWB 150 I did last year, RWS Hobbys were tied with H&N Finale Match Pistol pellets as the best ones. Go figure!
I shot two 5-shot groups each with the other 7 pellets. And with 6 of the 7 pellets, the second group was smaller than the first. That lends support to the notion that an airgun barrel needs to be seasoned before it will perform its best.
Honorable mention
The following pellets did okay, and I would have continued to use them if I had nothing better. Each of them seemed to want to do better than they were doing, but I tried an extended test with one of them and it didn’t pan out.
The RWS R10 Match Pistol pellet came the closest to making the final cut. Maybe if I shot it more it might improve. But the best group of five I got measured 0.153 inches between centers.
I tried the Vogel match pellet that Scott Pilkington makes here in the U.S. It’s a great match pellet, but for some reason the 300S didn’t care for it that much. This is the pellet I shot four groups with, but the best of them measured 0.192 inches between centers. No dice!
JSB S100 Match pellets were another tease. The best group measured 0.113 inches between centers, but in the end it just wasn’t enough to make the cut. This was the only pellet I tried that had a head size of 4.52mm. All the others were 4.50mm. This pellet did very well in an Edge match rifle from AirForce, so I thought it might have a chance here, but no dice.
The one domed pellet that I thought might work but didn’t was the Air Arms Falcon pellet. The best group out of two was 0.167 inches between centers. It was a nice, round group; and because this isn’t a wadcutter, the group looks about half the size it really is. With domes, you have to make extra allowances for the skirt that tears through the target paper.
The winners
Three pellets showed great promise in the 300S, and one of them was superb. The JSB Exact RS was the best domed pellet, putting 5 shots into a beautiful round group that measured just 0.111 inches between centers. Because these groups are all so small, I’ve enlarged the photos for you to see them better. My dime is in the photo for reference. This is the pellet I will take out to 50 yards.
JSB Exact RS pellets made a nice small, round group. They will be shot at 50 yards in this gun.
I tried both H&N Finale Match Pistol pellets and H&N Finale Match Rifle pellets in the 300S, and both turned in a wonderful performance. These are the pellets the gun likes best. The Finale Match Pistol pellets turned in a group that measured 0.117 inches between centers. It looked very good when I saw it, but one that’s even better was yet to come.
That’s a nice tight group of five H&N Finale Match Pistol pellets. It measures 0.117 inches between centers.
The best pellet of the day was the last one I shot — the H&N Finale Match Rifle pellet. Five of them went onto a group measuring 0.097 inches.
H&N Finale Match Rifle pellets made this group that measures 0.097 inches between centers. Now, that is a group!
So we found out what we knew all along: the FWB 300S is an accurate target rifle. Just for fun, I checked back to the test of the FWB 150 and saw that the best two groups with that rifle measured 0.119 inches between centers, so I did a little better with this one. On any given day, I suppose either rifle would emerge the victor. But I like the firing behavior of the 300S a little better.
The next time you see this rifle, it will have fired those JSB Exact RS pellets at 50 yards. What a day that will be!
FWB 300S vintage target air rifle: Part 2
by B.B. Pelletier
The FWB 300S is considered the gold standard of vintage target air rifles.
Some more history
The first part of this report was certainly met with a lot of enthusiasm, so I think I’ll add some more history today. In the comments to Part 1, we had a discussion of the sport called Running Target. Some called it Running Boar, which it was for several decades, and long before that it was called Running Stag.
The sport originated in Germany, I believe, though it was probably popular in Austria and perhaps even in Switzerland. It existed at least as far back as the mid-19th century and was shot outdoors at a target pulled on tracks by human power. The original target was a male chamois made of wood with a target where the heart of the animal would be. But that target evolved into a male red deer, called a stag. The stag was exposed to the shooter for a specific number of seconds.
In time, the stag was replaced by a running boar, because the stag was thought to be a noble animal and the boar wasn’t so highly regarded…though in England they did have a similar sport called Running Deer.
As the match evolved, it picked up rules. There was a slow presentation of the target (5 seconds) and a fast presentation (2.5 seconds), and the shooter was supposed to shoot one shot on each pass. The target was engaged in both directions during the match. It wasn’t long before the wooden animals were switched for paper targets that were both cheaper and easier to score.
The Running Boar target was double-ended so it could be used in both directions on the same track.
The aim point was usually the animal’s nose, but that was the choice of each shooter.
Over the years, the rifles they used changed from muzzleloaders to centerfires, and eventually to rimfires and airguns, because of the increased opportunities for range safety. Today, both rimfires and airguns are still being used at the World Cup level.
The guns have traditionally used sights that account for the movement of the target and allow the correct amount of lead. When scopes came into the event, they were specialized with reticles that allowed for the lead to be dialed in. Anyone who owns an FWB 300S Running Target rifle with the correct scope has something to prize.
Gary Anderson brought a running target range to the Roanoke Airgun Expo back in the late 1990s, giving many airgunners the opportunity to closely examine the target setup. By the 1970s, the sport had become Running Target — to assuage those who felt shooting at boars was not politically correct. The sport was part of the 1992 Olympics, but was dropped after the 2004 games. It’s a sport that goes in and out of fashion as the years pass; but it’s still a World Cup event, so we may see more of it in time.
When the change was made to Running Target, the target was changed to a target with one central aim point and two bulls — one for each direction.
Velocity of the FWB 300S
Today is the day we check the velocity of this FWB 300S, so let’s get to it. When it was new, the 300S was advertised with a velocity of 640 f.p.s., though the pellet they was used to get that number was never specified. I will use a range of pellets I believe are appropriate to the power level of a spring gun like this. And, in a departure for me, one of the pellets I test will be domed.
Air Arms Falcon
I tested the Air Arms Falcon pellet even though it’s a domed pellet that’s not appropriate for target shooting, because many readers use these rifles with scopes for plinking and other pursuits. So, I’ll also shoot this pellet for accuracy — just to see what it can do.
This was the first pellet I tested, and I’m so glad I own a chronograph, because I learned something valuable about the 300S in this test. This rifle needs to warm up before it’ll shoot with stable velocity. Think of an older car from the 1950s that had to be warmed up for a minute or so and then driven slowly for the first mile to allow the parts to expand and start sealing as they should. Heck — most car engines from that era developed leaks pretty quickly, and you did whatever was necessary to keep them from wearing faster than they should. Well, this FWB 300S needs the same kind of warmup. Let me show you the first 9 shots.
Shot Velocity
…1……543
…2……560
…3……580
…4……615
…5……635
…6……633
…7……639
…8……647
…9……656
So, if you shoot a 300S — or any of its derivatives — for score, maybe you better shoot about 10 shots just to warm the action before expecting the rifle to do its best.
After shot 9, the rifle became very stable and averaged 658 f.p.s. with the Falcon pellet. The low was 655, and the high was 671 f.p.s. At that speed, this pellet generates 7.05 foot-pounds. That’s pretty brisk for a 300S; but Mac, who traded the rifle to me, said it had just been sealed and overhauled by Randy Bimrose, so it’s performing at its best.
A couple observations
Before I move to the next pellet, I’d like to make a few observations. First, I said in Part 1 that the 300S action doesn’t need to be levered forward at the end of the cocking strike like the action of an RWS Diana model 54 Air King, but that was incorrect. It does have to be levered forward into lockup in just the same way, but the 300S action is so smooth that I didn’t notice it until now. With a Diana 54, you always notice it.
I mention this because, like the Diana 54, the 300S uses the sledge-type anti-recoil system; and even though it’s a gentle rifle, it has to operate in the same way as the more powerful Diana. Moving the action forward into lockup prepares the action to release when the gun fires and to move on the steel rails in the stock just a fraction of an inch, canceling the feel of recoil.
The second thing I noticed this time is that I can feel the cocking link bump over the mainspring coils as the cocking lever moves back to the stored position. I sometimes feel that same roughness in other spring rifles, where the tolerances are tight, and I thought I’d mention that this one does the same thing.
RWS R-10 Pistol pellets
Next, I tried the RWS R-10 Pistol pellet, which weigh 7 grains, even. I tried them because of their weight — not because I think they’ll be the most accurate pellet. I just want to show the rifle’s velocity with a reasonable range of pellet weights.
This pellet averaged 658 f.p.s. with a low of 640 and a high of 664 f.p.s. The low shot was the only one that went slower than 656 f.p.s. At the average velocity, this pellet generates 6.73 foot-pounds of muzzle energy.
H&N Finale Match Rifle pellets
The final pellet I tested was the 8.18-grain H&N Finale Match Rifle pellet. It averaged 609 f.p.s. and ranged from 597 to 616 f.p.s. The average velocity generated a muzzle energy of 6.74 foot-pounds
There you have it. This 300S is extremely healthy and ready to go target shooting in the next report! It’s still a joy to shoot and is a rifle that you should continue to covet if you’re so inclined.
One additional thing. There has been some talk of how accurate these rifles are at longer range. If you want, I’ll schedule a special fourth report in which I shoot this rifle outdoors at 50 yards. I’ll have to wait for a calm day, of course, but wouldn’t it be fun to see how this rifle shoots at that range?
Why do shot groups move?
by B.B. Pelletier
I couldn’t fit the entire question into the title, so here it is:
Why do shot groups move from side to side when the scope setting doesn’t change?
This question does not include different pellets impacting at different places on a target at the same range, which is caused by the individual flight pattern of each type of pellet. However, I’ll address that question before moving on with the first one.
Today’s question was suggested by Jay in VA, who really wants to know why different pellets or bullets shoot to different places, with respect to left and right. Jay, that’s caused by how each pellet or bullet is stabilized. Back around the turn of the 20th century, Dr. F. W. Mann conducted an experiment in which he locked a barreled action in a 3,000-lb. vice (his “Shooting Gibralter” rest, a concrete pier sunk 40 inches below ground level and extending about 30 inches above, and fitted with a cast iron lockdown rifle rest) and then fired the “gun” at 100 yards in still air. After each shot, Dr. Mann rotated the barreled action 90 degrees, until he had shot it in a complete rotation. His lockdown mount was constructed to allow this rotation, so the barrel was never unlocked from the rest.
The barrel was locked down and could not move except to rotate along the axis of the bore. Still, it shot to four distinct places, each separate from the other. One was when the barrel was straight up, the next was with the barrel rotated 90 degrees to the right, the next was rotated 180 degrees to the right and the last was rotated 270 degrees to the right. That gave four distinctly different points of impact at 100 yards. Some Pope barrels shot groups smaller than an inch this way, but other barrels with less pedigree produced four-shot groups as large as 16 inches.
So, if the SAME barrel shooting the SAME bullets shoots to four distinctly different places, depending on how the barrel is rotated on its axis, how do you think it will do when different bullets are used? That’s right, different points of impact. It has to do with the projectile’s rotational stability and the bullets finding their own path (trajectory) once they’re free of the confining restraint of the barrel. We might like to think that bullets travel along a precise path, but it isn’t always true. Sometimes, they have to diverge to the path that’s dictated by their own inherent stability. Archers know this more than riflemen, because arrows have their own independent flight rules and the experienced archer learns what each arrow wants to do.
The real question
But that isn’t the question I want to address today. I want to talk about this: When a scope is sighted in at one distance, it will shoot to the left or right of the point of aim at a different distance. There are two main reasons for this.
Unstable flight
The first reason for this is the fact that some pellets spiral in flight. In other words, as they travel downrange they don’t remain on a straight line; rather, they travel in a spiral that goes in the same direction as the spin introduced by the rifling. A righthand-twist barrel can produce a pellet that flies with a right-hand spiral. You don’t have to take my word for this, you can watch it for yourself on You Tube. The man who made and narrates that video calls the spiral a wobble, but we’re talking about the same thing. He found it was caused by a dirty bore, but I’ve seen the same thing through the scope when using certain pellets that were not suited to a particular barrel. Clean or dirty barrels aside, those pellets always spiraled.
The video shows a pellet losing stability and spiraling from that loss, but a pellet can also be inherently unstable and always spiral. When that happens, the pellet will group at different points around the point of aim, depending on the distance the gun is from the target.
You don’t need a high-speed camera to see this. How do you tell if you have this problem? Simple, shoot three groups at three different ranges. Make the sight-in range the first target and the other two farther away. If they look like the ones shown here, your pellets are spiraling.
Gun sighted-in at 25 yards. Pellets are centered.
Same gun with same sight setting but shooting at 20 yards.
Same gun and same sight setting but at 30 yards. This pellet is spiraling.
Scope misalignment
A more fundamental cause of groups moving from left to right is caused by a slight scope misalignment, in relation to the bore. If the bore is pointed at 360 degrees and the optical axis of the scope is pointed at 5 degrees (that would be 5 degrees to the right of where the barrel is pointed), the shooter will adjust the reticle to bring together the point of impact and point of aim. Let’s say he does this at 25 yards, where the pellet hits the point of aim. If the scope is misaligned as I am describing, then at 20 yards it’ll group to the right of the point of aim, and at 30 yards it’ll group to the left of the point of aim. Where it hits depends on how the scope is misaligned, of course.
At 25 yards, the gun hits the point of aim.
At 20 yards, the pellet strikes low and to the right.
At 30 yards, the pellets strike high and to the left.
This type of “scope shift” will always go in the same direction. The farther out you shoot, the more to the left the groups will be; the closer you shoot, the more they’ll move to the right. They’ll always maintain this right-to-left relationship and will never reverse directions. That’s a diagnostic you can use if and when such a problem arises.
While the above two sets of targets look similar, they were created by two very different effects. In the first set, the pellet’s moving in a righthand spiral that’s increasing in size as the pellet moves farther from the muzzle. In the second set of targets, the pellets are shifting from the low right to a high left position and will keep moving in a straight line away from the aim point (to the left) as the distance to the target increases.
A spiraling pellet moves from one side of the target to the other and back again as the range increases.
A pellet shift caused by scope alignment always moves in the same direction — in this example, right to left.
Pellet shift diagnosis
Here’s how you figure out what the problem is.
Are the pellets moving from side to side and back again as the range increases? That’s a spiraling problem, and the dispersion (distance from the aim point) increases with the distance. The solution is to use different pellets or perhaps to clean the bore.
Are the pellets shifting in one direction and only as the range increases? That is a scope alignment problem, and the scope needs to be realigned to correct it.
Don’t be discouraged
This problem confounds shooters all the time, and it’s often the root cause of a misdiagnosed scope shift problem. Don’t be discouraged after reading this report. You can mount a scope accurately enough that you will never encounter this kind of problem.
Knowing that gives you power over these two common problems. If you know they exist, you can watch for them and make corrections when necessary.
