Posts Tagged ‘Crosman Nitro Piston Technology’
by Tom Gaylord, a.k.a. B.B. Pelletier
Before I begin today’s report, I have sad news. Our friend Earl “Mac” McDonald passed away on Sunday, May 5, at 4:30 a.m. He was surrounded by his family.
Mac was diagnosed with a prion disease in April of this year. I don’t want to discuss it here, but if you want to know more, here is a link. This disease affects one person in a million. It is not only very rare, but the cause wasn’t even discovered until the 1980s. Scientists are still unsure of all the details.
I was aware of the probable diagnosis when I went to visit Mac last month but was asked not to disclose the details. Fortunately, when I arrived, he was able to recognize me. I sat with him and talked about old times whenever he was awake. My wife, Edith, and our friend Otho Skyped with Mac. Via the computer, Edith showed Mac the SHOT Show report in Shotgun News, which was the last thing he photographed for me.
Like everyone who knew him, I’m saddened by his passing — but that is more than offset by the pleasure of knowing him as long as I did. The fact that he was able to attend this year’s SHOT Show was especially rewarding.
As this blog moves forward, I will occasionally refer to Mac and some of the things he did. The best memorial I can give him is to never forget the time he was here.
I left you with a cliffhanger last Friday — more than I imagined, as it turned out, because I thought I was writing Thursday’s report and would publish the second part on Friday, rather than today. I know you all want to know what happened when I seated the H&N Finale Match Pistol pellets deep in the bore with the cocking aid attached and rested the pistol directly on the sandbag.
If you were expecting a Cinderella story, it didn’t quite happen. The group got measurably better — in fact, it was the second-best group of the test to this point. Ten shots made a group measuring 1.105 inches between centers. Compared to the previous group, which was larger than 2 inches, it seemed clear that this was the best way to shoot this pellet — deep-seated, gun rested on the bag and the cocking adapter attached.
Ten shots with H&N Finale Match Pistol pellets seated deep with the cocking aid attached and the gun rested directly on the bag made this 1.105-inch group. So, deep-seating these pellets reduced the group size by half.
Did you possibly think that it put all 10 into the same dime-sized hole that the 5 good ones went into on the previous test? I hoped that would happen, too, but it didn’t.
Not H.P.White Labs
Before you start looking back at all the testing done on this pistol to-date to recommend different things for me to test, let me say I am not H.P. White Laboratory, and the goal of this test is not to see how accurate the Benjamin Trail NP pistol can possibly be. My purpose is to evaluate the pistol as it comes from the box, so those thinking of making a purchase will have something to go on. I think I’ve done that already, and the gun is definitely worth the money. But the test is far from finished.
Air Venturi Pellet Seater
Blog reader Nomobux asked me how deep I seated the pellets with the Air Venturi Pellet Pen and Pellet Seater. Well, that varies, based on how thin the pellet skirts are. But I measured the seater with the pin protruding by 0.163 inches, which seated the pellets about 0.125 inches deep.
A blog reader asked me to test Crosman Destroyers — a new hollowpoint that has a large open cavity in the nose. Since I was playing, I decided to shoot 5 shots and see if it was worth finishing the group. With the pellets seated deep, the cocking aid attached and the gun rested directly on the bag, 5 shots made a group measuring 2.546 inches, so I stopped there. Since that was already very large and 5 more shots would not make it any smaller I decided to save my time and effort.
Five shots with Crosman Destroyer pellets seated deep with the cocking aid attached and the gun rested directly on the bag made this 2.546-inch group. I stopped after 5 shots because the group was already too large.
But I also figured some of you wouldn’t let me rest if I didn’t test at least one more variable with this pellet, so I shot it seated flush, as well. Surprise! It turned out better. Ten shots went into 2.086 inches. That’s not a world-beater group, I know, but it is better than the 5 shots with deep-seated pellets. It points out that deep seating has to be evaluated on a case-by-case basis.
Ten shots with Crosman Destroyer pellets seated flush with the cocking aid attached and the gun rested directly on the bag made this 2.086-inch group. Though it’s not a great group, it is better than the 5-shot group with deep-seated pellets.
Michael, Michael, Michael!
Blog reader Michael saw that I hadn’t yet tested the best-shooting RWS Hobby pellets from the rested position with the cocking aid attached, but he was standing on my shoulder as I played with the pistol. I knew you would want me to go back and test it this way, so I did. This time, the magic didn’t work, however, and the 10-shot group size was 1.536 inches, so no improvement.
Isn’t it interesting how changing one variable will change the entire performance of the gun? I think so.
The bottom line is that the Benjamin Trail NP is still a whole lot of value for the price tag. And I’m not finished, yet. There’s still another accuracy test to go with those lead-free pellets; and then I want to recheck the velocity of the gun, now that several hundred shots have been fired. There’s more to come, so sit back and enjoy.
by Tom Gaylord, a.k.a. B.B. Pelletier
Today we’ll make blog history. This is the first half of a 2-part report on the Benjamin Trail NP pistol. I was shooting it yesterday and found myself going in so many directions that I collected too much data for a single report. So the second half of today’s report will come on Monday.
I told you in the last report that I decided to “play” with the pistol rather than subject it to a rigidly structured test. Well, that must be catching because I did it again today. Something about this air pistol seems to invite experimentation.
It doesn’t have to shoot low!
I said that it shot too low in the last report. It did, but I was using the sights in a way the manufacturer did not intend by using the tip of the front sight for a 6 o’clock hold. That caused the gun to shoot a little low by itself. But, today, I replaced the rear sight with a red dot sight and found that the gun can shoot to the point of aim with ease. In fact, I had to adjust the sights down, but I will talk about that later.
I mounted a Tasco Pro Point dot sight on the 11mm dovetails that are on the rear of the spring tube. You could use anything that has a decent amount of adjustability.
It’s so much easier using a dot sight because there’s just the dot and target to watch, instead of the sight alignment. Shooting the pistol was much easier.
The first pellet: RWS Hobby
In the last test, RWS Hobby pellets were the most accurate, so those were the first pellets I tested this time. That made it simpler to test the gun because I knew I was starting with a reasonably accurate pellet.
And because this will become important in a while, let me tell you that these first groups were shot without the cocking aid on the gun. It’s a little harder to cock without the aid, but installing and removing it for every shot takes too much time.
The first group surprised me, because it wasn’t as good as it was the last time I tested this pistol. The first shot was a low flier caused by my unfamiliarity with the dot sight; but after that, all the rest of the shots were the best I could do. I think the measurement for 9 shots is more representative in this case, and let’s exclude that one low shot.
Nine shots went into a group that measures 2.04 inches between centers. That’s still larger than the group I got with open sights, which is 10 in 1.155 inches. I wondered if some of the stock screws might have loosened in all the shooting. I checked, and they certainly had. I tightened all stock screws; but instead of running the same test again, I proceeded to the next test. How would the pistol respond to pellets seated deeply with the Air Venturi Pellet Pen and Pellet Seater?
Not only did the group improve measurably, the point of impact rose by two inches when I seated the pellets deep into the breech with the pellet seater. This pellet seater is really proving to be a valuable piece of equipment when used on certain guns — like this one. And this rise in the point of impact is why I say there’s no problem with the Trail NP shooting low. You simply need to seat the pellets deeply.
This time, 10 RWS Hobbys went into 1.025 inches between centers. That’s remarkably close to what I did last time with open sights, but just a trifle better.
Since deep-seating seemed to produce such good results, I decided to seat all pellets from this point, on. For my next test, blog reader Victor suggested that I try some good competition pellets. He recommended some H&N pellets, so I selected H&N Finale Match Pistol pellets. I seated them deep and proceeded with the test. But, oh, my, they didn’t do well at all! At least not when taken as a whole.
Five of those pellets managed to make a very tight little group. They gave me hope that this pellet wasn’t as bad as the numbers said. Perhaps something more was required?
The dot showed that I was shaking a lot more than I was comfortable with, despite using a two-hand rested hold. My forearms were resting on a sandbag, and the pistol was held in my hands, just in front of the bag. It sounds like a solid rest, but the dot said otherwise.
Since I was playing with the gun anyway, I stopped shooting for score and started experimenting with different holds that were firmer. I tried using my off hand as a modified artillery hold, but that was just as shaky. Then, I laid the gun directly on the sandbag and had a go. That proved to be the best way to hold it, as all shaking stopped and the pellets landed together again.
I also thought that if I was going to rest the gun on the bag, I might as well use the cocking aid again, too. I had now fired the gun about 50 times in all and wanted to relieve some of the strain on my hands. So the cocking aid went back on the gun.
And that’s all I’m going to tell you today. Tune in Monday to see if this new position paid off.
by Tom Gaylord, a.k.a. B.B. Pelletier
Accuracy day has arrived. And this is going to be a report that’s different than the ones I normally write because I decided to do things differently with the Benjamin Trail NP pistol. First of all, there’s some interest in the gun. Readers have said they’re watching the reports because this gun seems to deliver a lot of performance for a very reasonable price.
Next, I’ve read some owner reviews that talk about the gun hitting low. I wanted to test that for you. Owners also say the pistol shoots to two different impact points, depending on whether or not the cocking aid is attached.
Finally, I received a call from Crosman’s head engineer, Ed Schultz, who noticed I was testing the pistol now. Ed confirmed that the pistol does indeed shoot to two different points of impact, depending on whether or not the cocking aid is attached. He was also intrigued by how much I seem to like the air pistol, so we chatted about that for awhile.
How this test will be different
I decided to “play” with this pistol today instead of plowing through a formatted test with X number of pellet types. What that means is that I decided to let the pistol lead me through the test, and to look at those things that were interesting — even if they didn’t conform to my normal test format. I think the test went well, but it lead me in directions I might never have taken otherwise.
It shoots low
The first pellet up was the RWS Hobby. The first shot wasn’t even on the paper, so I elevated the rear sight as high as it would go, then I held up the front post above the rear notch in a style that was popularized by Elmer Keith. That got me on paper, and I put 10 shots through the gun. They landed in a group that measured 1.155 inches between centers. This turned out to be the best group of the test, and I think it shows the accuracy potential of the pistol quite well. You see, I was estimating how much front post to hold up above the rear notch while I shot this group, so my aim point was only an estimate.
When Elmer Keith wanted to shoot handguns farther than their sights would allow, he used this holdover sight picture. Keith inlaid gold lines on his front sights, but I am simply estimating the height from shot to shot.
Even when I held over a lot, the pellets landed below the aim point. So, I used another trick by drawing a secondary aim point above the main bull and using the holdover sight picture on it (at 6 o’clock). My sight picture now looked like the drawing above.
Next, I tried the lead-free Crosman Powershot Penetrators. Using the higher aim point, I put 10 of them into a group that measured 2.527 inches between centers. Obviously, they’re not right for this pistol.
Different impact point?
I told you I was playing with the pistol, so next I tried an experiment to see the difference in point of impact when the cocking aid was left on the gun or removed during firing. And there was a difference! For this test, I used JSB Exact RS domes.
I used the same high aim point, and the pellets landed about 2 inches lower when the cocking aid was left on the barrel during firing. I’ll show both groups on the same target, so you can see what that looks like.
The group fired with the cocking aid installed was slightly tighter than the one with it removed. The one with the cocking aid measures 1.369 inches between centers, while the other group measures 1.636 inches.
I reported that the cocking effort is low for this pistol. Well, that’s fortunate; because when I shot it without the cocking aid, I also cocked it that way. The effort required with the aid installed still measures 25 lbs., and with the aid removed it increases to 35 lbs.
This time, I shot the pistol indoors, and I still must say that it’s very quiet for the power. I think some new owners may have had a few detonations when their guns were new and thought their pistol was going to always be that loud, but I doubt that many will fault it for the sound after it calms down.
The trigger-pull isn’t so much heavy as it is long. It does take some concentration and even discipline to shoot the pistol at its best. But there’s no creep in the second stage.
Crosman Premier heavies and JSB Exact 10.34-grain heavies
I had thought that heavier pellets might do best, so I tried both Crosman Premier heavies and JSB Exact heavies. Since I was just playing with the gun instead of conducting a formatted test, I decided that if either pellet didn’t show any promise by 5 shots, I wouldn’t complete the group. Well, neither one did, so I ended each group at just 5 shots. Both would have been over 2 inches for 10 shots.
Crosman Premier lites
The last pellet I tested was the 7.9-grain Crosman Premier lite, figuring that if the heavy didn’t group, the lite might. And that was correct. The lites gave me a 1.775-inch group, which doesn’t sound good. But 9 of those pellets are in 1.314 inches, which is a lot better.
What’s the verdict?
The verdict is — it’s too soon to tell. I still have some things to test with this pistol. For starters, the sights that are on the gun are so problematic that I want to try it with a good quality dot sight and see what I can do. If I can adjust the sight so I’m able to aim at what I’m hitting, and if I use the 3 pellets that worked well in this test — RWS Hobbys, JSB Exact RS and Crosman Premier lites — then we might just see a more accurate gun.
I also want to test pellets that are seated deep in the breech to see if there’s any difference. There are the two lead-free pellets that Crosman sent, but I didn’t get around to testing this time. I’d also like to run a velocity test after all of that because, by then, I think the gun should be broken in.
More than ever, I think Crosman should build this gun as a carbine, using exactly what they have here but with an extended barrel shroud and a rifle stock. As easy as it is to cock as a pistol, I can see it losing another 10 lbs. of effort as a carbine. What a wonderful little plinker it would make!
by Tom Gaylord, a.k.a. B.B. Pelletier
Okay! The moment of truth has arrived. It’s velocity day for the Benjamin Trail NP pistol that claims to shoot 625 f.p.s.
I am still at my friend Mac’s home on Maryland’s eastern shore, so I brought the chronograph with me. I also brought some pellets I wanted to test, as well as all 3 types of lead-free pellets that Crosman sent with the pistol.
The first pellet I tried is the lightweight lead RWS Hobby. This pellet fits the bore very tight, so I may come back and test it seated after the accuracy test. Seated flush, they averaged 494 f.p.s. The range went from 477 to 509 f.p.s. That’s a spread of 32 f.p.s. Remember that Crosman said this pistol would have a wide velocity range for several hundred shots when it breaks in. At the average velocity, this 7-grain pellet generates 3.79 foot-pounds of energy at the muzzle.
I can hear the naysayers warming up now. But hold onto your skirts, because this pistol is about to come alive.
Crosman SSP hollowpoint
The first pellet that Crosman sent me to test with the pistol was their lead-free SSP hollowpoint. This one weighs exactly 4 grains and looks like one of those new high-performance hollowpoints that performs well at lower speeds. In the NP, the average velocity was 632 f.p.s., so that substantiates the Crosman claim. The spread went from 531 to 697 f.p.s., but that first shot was way out-of-profile. The second slowest shot was 597 f.p.s., and the bulk of the shots ran between 630 and 660.
So — what’s the power of these lightweights? How about 3.55 foot-pounds? However, I don’t think this string is really representative of the pistol because of the other SSP pellet I tested later.
Crosman Powershot Penetrators
Next I tried Crosman Powershot Penetrator. They are a synthetic-bodied pellet with a metal nose. Crosman guarantees them to be 20 percent faster than lead pellets. They weigh 5.4 grains, and in the NP pistol they averaged 576 f.p.s. The spread went from 561 to 586 f.p.s., so it’s tightening up quite a bit. I do feel this is more of the break-in process, rather than the specific pellet, though I don’t want to take anything away from these Powershot Penetrators.
Like the SSPs, this pellet also fit the bore loosely. And the average energy was 3.98 foot-pounds of energy at the muzzle. I really can’t wait to see how accurate these are because they look like they might have a lot going for them.
Crosman SSP pointed pellet
The next pellet tested was the Crosman SSP pointed pellet. Like the SSP hollowpoint, it also weighs 4 grains, yet this one went so much faster on average that I believe the pistol was breaking in right in front of my eyes. The average was 685 f.p.s., with a spread from 667 to, get ready for it — 704 f.p.s. Yes, the pistol broke the 700 f.p.s. level with lightweight pellets. Crosman has to advertise the highest velocity the pistol is capable of achieving, so setting the bar at 625 f.p.s. is conservative.
At the average velocity, this pellet generated 4.17 foot-pounds of energy at the muzzle. Because it weighs the same as the hollowpoint SSP and fits the bore the same, I think the pistol is still breaking in.
JSB Exact RS
The last pellet I tested was the JSB Exact RS dome. I included it because of the accuracy potential. Although it’s light like the Hobby, it has a thinner skirt, so it was anyone’s guess how it would do in this pistol (because the gas piston is known for blowing pellet skirts out from the sudden pressure spike).
They averaged 487 f.p.s., but the range was tight — from 480 to 499 f.p.s. At the average velocity, this 7.3-grain pellet developed 3.85 foot-pounds of energy at the muzzle.
Next, I weighed the trigger-pull. It is two-stage, and stage one weighs about 3 lbs., while stage two breaks at 7 lbs., 3 oz. on the test gun. I have to observe that the design of the grip makes the trigger-pull seem a lot lower. I had guessed it to be 5 lbs. before putting the gauge on it.
I shot this test outdoors, so the sound was different than usual. But I must say the discharge is very quiet for a gun of this power.
This pistol remains easy to cock. In fact, I shot it about 60 times in this test because there were a number of shots that didn’t register on the chrono. And I wasn’t tired at all at the end of the shooting. This is an all-day gun for sure.
But the cocking assist came off the muzzle a couple times as I was closing the barrel. It held tight when the barrel was cocked, but popped off several times when the barrel was closed. The trick is to not hold it out at the end, but, instead, under the muzzle when you close the barrel.
The pistol cocks with exactly 25 lbs. of force. The effort ramps up to 25; and just when you think it will go even higher, it drops off. This is an all-day air pistol for any adult. I don’t know how they did it, but the Crosman engineers are to be commended.
Impressions so far
I’m still very impressed with this pistol. It cocks easier than I thought possible and shoots smoother than it should for the price. I can’t wait to see what it can do on targets!
by Tom Gaylord, a.k.a. B.B. Pelletier
There’s been a lot of talk about this new breakbarrel air pistol from Benjamin — the Benjamin Trail NP pistol. First and no doubt foremost is the price — just $80 at launch time. When you consider the power this pistol is rated to — over 600 f.p.s. with lightweight alloy pellets — you can understand the interest. You get the power of a Beeman P1 or a Diana RWS LP8 for a fraction of the price.
Yeah, but is it accurate? I don’t know yet, but you all know I’m going to test the heck out of this pistol to find that out.
But in the back of many minds is that NP label, which we know stands for Crosman’s Nitro Piston. That’s the brand name they use for the gas springs they put in airguns, and this is the world’s first pistol to get one as far as I know. If anyone knows different, please speak up.
So, a gas spring is often hard to cock. In fact, that’s the single disadvantage to the technology, in my mind. But not all gas springs are hard, and Benjamin has offered certain Nitro Piston rifles in the past that were quite easy to cock. Then what’s the story with the Trail NP pistol?
No worries, mate! Old B.B. has already cocked the gun. I have the news you have been waiting for. This 65-year-old codger says the Benjamin Trail NP pistol is very easy to cock. Let me put that into perspective for you. I think this pistol is in the same difficulty class as the two pistols I compared it to — the P1 and LP8. In other words, this isn’t for a young person, nor for anyone who doesn’t mow their own lawn with a push mower or ride a bicycle; but if you’re in reasonable shape, you’ll find the Benjamin Trail NP remarkably easy to cock.
I am not going to tell you exactly how hard it is to cock until the Part 2 velocity test, but I’ve already put it on the scale and I know the number. The Crosman engineers designed the pistol with the optimum cocking linkage and pivot point. Just when you think the effort is going to soar, it actually falls off sharply — giving you a pleasant surprise. As far as I’m concerned, Crosman should put some sort of trademark on this pistol’s cocking effort like “POW-R BOOSTER” (or something similar). Even if there’s no special or patentable technology involved, they’ve crossed the line and given us not only the world’s first air pistol with a gas spring, but also one that’s easy to cock.
In fact, I would like to see this pistol turned into a small rifle. They don’t need a longer barrel — just a barrel sheath that takes the front sight out farther, and a stock to hold the action. It would be a sort of Air Venturi Bronco with a gas spring. How cool is that?
Think I’m impressed? YOU BETCHA! This is the second time in 2013 that I’ve had the pleasure of testing a remarkable new airgun with impressive technology. The LGVs were first, and now this Benjamin Trail NP is something else that makes B.B. smile! I haven’t done much of that in recent years. I see so many clones that all seem to blend together with too much weight, cocking that’s too hard and a nerve-shattering firing cycle. But this new pistol is smooth.
Ooops! Did I just slip and reveal that I’ve also fired the new Trail NP? Why, yes I did. I’m not going to elaborate today because I need material for the Part 2 velocity report but, believe me, this pistol shoots smooth.
Okay, B.B., quit hyping this pistol and tell us about it.
The gun I’m testing is a .177 breakbarrel that’s fairly straightforward, except for the Nitro Piston. Being a breakbarrel, it’s also a single-shot because the barrel must be broken open every time to both cock the spring and to load the next pellet.
It looks like a large air pistol. The grip is actually a stock that holds the entire barreled action, so the spring tube sits high above the hand. You would think that would make the pistol recoil — and it would if this was a firearm — but since it’s an airgun and one with a gas spring, the recoil is quite light.
The grip/frame is synthetic, which it should be for the price and also to keep the weight off. The grip has large rectangular knobs that provide a good grip. The pistol weighs 3.46 lbs. and balances surprisingly well. It looks very front-heavy, but that cocking aid is just hollow plastic and weighs almost nothing. And speaking of the cocking aid, you leave it on the pistol while shooting. When it’s off, the pistol is about the same size as the Beeman HW 70A we’re currently testing.
The front sight is fiberoptic. Unfortunately, the top is rounded instead of being flat, so it’s going to be harder to obtain a sharp sight picture. With proper lighting of the target, it should be possible.
The rear sight is also fiberoptic, plus fully adjustable for both windage and elevation. each adjustment knob has crisp detents that leave no question about the movement. I’ve seen guns for twice this much that didn’t have sights as nice as these.
The trigger is single-stage and adjustable for the break point. I don’t know how they managed to pack that feature into an $80 pistol that’s also the first of its type. Of course, I’ll report on its performance, but something in the owner’s manual made me stop and take a second look.
The owner’s manual?
I know, it’s very girly to admit I read the manual, but I wanted to find out about the trigger adjustability. However, in this manual I found more. Just after the introduction to the parts of the gun, they have a short paragraph about the break-in period. They tell you that accuracy may be inconsistent during this period, and that the gun may sound louder than it will later on. That blew me away! Not that the gun needs to be broken-in, but that a manufacturer acknowledged it and even addressed it in the manual. In the bad old days, you were either expected to know such things or get out of airgunning altogether. I joke, but it’s not far from the truth. It’s one big reason that I became an airgun writer in the first place.
What this passage indicates is that someone at Crosman spent some time with the pistol and put their findings into the owner’s manual. That sort of thing is very uncommon these days and is one more indication that Crosman is serious about what they’re making.
I guess I gave you all of my first impressions at the start of this report. But I’ll say one more thing. Putting a gas spring into a pistol is a daring move. It’ll bring many initial sales to those whose curiosity has to be satisfied at all costs; but if the pistol doesn’t perform, it’ll quickly get a black eye from word-of-mouth on the internet. All companies must know this, but many of them act as if they don’t care or don’t appreciate the power of this kind of publicity. They must think that the novelty and power of their airguns will trump any bad press it gets on the internet. If they have an established distribution network in the large retail outlets, it can last for a long time; but if they don’t, this kind of bad press will kill them.
Crosman does have one of the largest distribution networks, yet they obviously still appreciate what their customers think. That fact is demonstrated by this new pistol. They could just as easily have made it hard to cock and shoot with a harsh firing cycle as gas springs are so prone to have, but they went beyond that and built a powerful pistol with a very acceptable cocking effort and a smooth firing cycle.
The Benjamin Trail NP pistol has my attention!
by Tom Gaylord, a.k.a. B.B. Pelletier
Today, blog reader Vince continues the saga of converting a steel spring rifle to use a gas spring. We last read about this project in Part 2 of I’ve got gas, where he showed us the pitfalls of making such a conversion to a Gamo breakbarrel. Let’s see how he does the second time around with a Crosman rifle.
If you’d like to write a guest post for this blog, please email us.
Back when I tried reworking the Crosman gas spring retainer, I discovered that drilling a straight and properly located hole on a round surface is a bit, well… tedious. And hard to do, at least without the proper drilling jig.
Of course, it would be very expedient to use the spring tube itself as a jig. After all, it’s perfect — as long as I can keep from damaging it, that is — because all the holes are obviously already in the right places. Put the retainer in place, pop in the pin and go at it through the existing bolt hole.
Two minor problems became apparent. First, the hole is too large to properly guide a 1/4-inch bit. Second, the edges of the bit might damage the existing hole in the spring tube. But both problems have an obvious, simple and cheap solution: a bushing.
A bushing for under $1.00 from McMaster-Carr.
I got mine from McMaster-Carr (part #2868T44) for less than 70 cents. If you’re feeling rich, you can probably get an equivalent at Home Depot for about $3.00. The important thing is that it has a 1/4-inch inside diameter, a 5/16-inch outside diameter, and that it be made from brass, bronze or steel. Plastic probably isn’t a good idea.
The process is simple — and THIS time I’m doing it on a Crosman rifle instead of a Gamo. No particular reason, I just wanted to show that it works on the Crosman platform as well. Specifically, this is a Crosman Sierra Pro, but mechanically it’s the same as the other Quest variants.
It looks like a Gamo, talks like a Gamo…
I ran into a bit of a problem sliding out the piston — it seems that the scope stop screw that I identified in this picture was binding the piston. Backing it out one turn solves the problem. As expected, the threaded hole in the Crosman gas spring retainer doesn’t align with the one in the spring tube — just like the Gamo.
The Nitro-Piston gas spring retainer…
…and why it doesn’t work.
So, what we’re gonna do is turn it 90 degrees and drill a hole on the other side.
This is where we have to drill.
See that little ledge sticking into the hole? I’m going to grind it out of the way:
Ground a flat spot, just in case.
In retrospect, though, this step may have been unnecessary.
Setting up the jig is about as straightforward as it gets. After installing the gas spring retainer and securing it with the retaining pin, I place the bushing in the hole in the spring tube and start drilling. The steel is pretty soft, so it’s not that difficult.
The bushing sits in the hole and is the jig for drilling. Simple!
But I only drill about half way and for a very good reason. If I keep going like this, I’ll hit something I don’t want to hit. Not a water or gas main, but that retaining pin is very definitely in the path of that drill bit. The solution is to slide the pin almost all the way out (but still engaging the retainer on one side); so when the bit breaks through, the pin won’t be damaged. Drilling the rest of the way thus proves uneventful.
Don’t want to drill through that pin.
Next comes the tapping — M8×1.25 inches, which is very close to 5/16-inch NC. If you don’t have a metric tap, get one. Do NOT try to make the SAE size work. You’ll regret it if you do! But my old and worn tap steadfastly refuses to start because it wants something a tiny bit bigger than 1/4 inch, so I have to bore out the hole to 17/64 inches. That makes all the difference, and a few minutes later I have a properly tapped hole.
Just a smidgen bigger…
…before I can tap the hole.
A quick test-fit shows that everything goes together just as it should.
As for the rest of the work, it’s a simple matter of cleaning everything out, lubrication and assembly. If you recall, the gas spring got scratched up from rubbing on the piston in my Gamo 220, so I colored those scratches with a Sharpie. That way, if I wind up with more rubbing in the same place, it’ll be readily apparent.
After a good cleaning, everything goes back together just as I described for the Gamo. But don’t forget that little disc that goes into the retainer.
I suspect this may be important.
One thing I sort of glossed over last time is how to get that pin installed. Since the gas spring has all of about 1/8 inch of preload, the pin can be started using a screwdriver to pry the retainer into place.
Prying the retainer to start the pin.
That’s good for getting the pin started. But you won’t be able to get it the rest of the way through because that spring is still pushing the retainer rearward, and the itty-bit of slop in the whole thing means that the holes won’t quite line up on the other side of the tube.
The solution is easy enough. Once it’s started, tap the pin in until it gets to that point. Then, lay the action on its side with the protruding pin downward, and push down on the spring tube while tapping the retainer with a hammer or mallet. The impact of the hammer will make the retainer jump forward just enough to momentarily line up the holes and allow the pin to start coming through. Three or four taps ought to be enough.
Tapping the retainer allows the pin to slide home.
The only minor difference between this Crosman gun and the Gamo is the endcap, which on the Crosman slides inside the tube. It’s a little different from the one that comes installed on the springer:
The gas spring endcap is on the left, the original on the right.
The gas spring version just slides into the rear after it’s all together, and we’re done!
Don’t forget to tighten the scope stop screw.
The action reinstalls in the stock with no mismatched screw holes.
Shooting it demonstrates the same sort of changes in behavior as with the Gamo I converted, only more so — and less so — all at the same time. For one thing, it runs a little hotter than it did in the Gamo. With the same RWS Basic pellets, it did the following:
That’s an average of just about 1000 f.p.s., or 15.5 foot-pounds of energy. This represents an improvement of just about 100 f.p.s. over the original Crosman powerplant.
Firing behavior and feel, however, wasn’t as vastly different as it was in the Gamo. The Crosman “sproings” a fair bit less than its Spanish forebearer (the rear guide tends to be a tighter fit); and with a tarred spring, the smoothness of the firing cycle is pretty close to that of the gas spring.
After I returned the Crosman to its original configuration, I was able to examine the gas spring for any damage. Oddly enough, there was some scratching again but nowhere near as bad as the last time and only on the front 1 inch of the cylinder. So, it’s not related to the centering of the gas spring at all. I suspect the end of the cocking link may have been rubbing it.
I remember a while ago a reader asked about the specs of the gas spring, in particular its pressure. I decided to measure that using my high-precision bathroom scale (!) and a Chinese hydraulic press. This was a quick and dirty way to get a ballpark figure. The pressure was almost constant as it was compressed but not quite. It did creep up just a bit, starting at about 130 lbs. and ending in the vicinity of 150. Overall length of the spring is 10.25 inches with a cylinder diameter of 0.715 inches.
And that pretty much wraps up my gas attack. Exactly where does that leave us?
Well, we’ve shown that the gas spring conversion is certainly doable. It’s not as straightforward as I would have liked — buy a few parts and stick ‘em in — but it’s not beyond the realm of the average handyman. The gas spring itself pretty much lives up to its reputation… smoother, somewhat harder to cock for a somewhat elevated power level. The big mechanical advantages — no coils to break, no degradation from being cocked for long periods of time — are already well-known. The main subjective advantage, the smoothness of the firing cycle, all depends on how bad was it to start with. In a 10-year-old Gamo, the improvement is likely to be rather spectacular (especially in an untuned gun), but if the rifle is already a smooth shooter, less is going to be gained. I guess it just comes down to personal preference — whether it’s worth $50 and a couple hours of your time is up to you.
by Tom Gaylord, a.k.a. B.B. Pelletier
Today, we’ll finish the conversion of a Gamo 220 from steel spring to gas spring, and blog reader Vince gives us a report on the outcome.
If you’d like to write a guest post for this blog, please email us.
Take it away, Vince!
When we last saw the Gamo 220, I’d disassembled the powerplant and compared the old parts to the parts I ordered from Crosman. Today, I’ll install those new parts and test the gun for you.
The gun is laying on the bench, ready for assembly. The new piston slides in, followed by the gas spring. Be careful when sliding the piston seal past the end of the cocking slot and tuck the soft seal material away from the sharp edges of the cocking slot so the seal isn’t damaged. A flat-bladed screwdriver works well for this.
The new piston that works with the gas spring is slid into the spring tube. Notice that I’ve lubricated both ends of the new piston with moly grease.
The new gas spring (Nitro Piston) slides in after the piston. The small end of the spring fits into the socket inside the new piston I mentioned in Part 1. No lubrication is required.
The trigger and cocking link go back in (reverse order of removal), and the plain plate gets dropped into the rear spring retainer.
I’m dropping the plain plate into the rear spring retainer.
Now, I’m starting to sweat a bit. You see, I KNOW that the gas spring has a TON of pressure on it even when fully extended (very much unlike a coil spring) — so, how on earth am I gonna compress it enough to reassemble the gun? Oh, well, I’ll cross that bridge when I come to it –which is, well, right about now. After I install the rear retainer, I notice something.
There’s almost no preload on the gas spring
Almost no preload at all! THAT’S right. Because the gas spring is ALWAYS at or near full pressure, there’s plenty of preload pressure as soon as the piston comes off its stop, so very little preload travel is required.
What is preload?
When a conventional coiled steel mainspring is installed in a spring gun, it’s usually longer than the space into which it must fit. It is, therefore, necessary to compress the spring by some amount to get it to fit inside the spring tube. This compression causes the spring to be under pressure even when at rest — this is called preload. If you’ve ever seen a long, empty flatbed trailer on the interstate that looked bowed up in the center because there’s no weight on it, you’ve seen what no preload looks like. It takes several tons of weight just to get that trailer flat again — and much more to make it bow the other way.
Airgun tuners can add spacers that preload the mainspring even more when it’s resting, which causes it to develop greater power when compressed because it’s closer to its maximum potential that exists at the point when all the coils are touching. But gas springs don’t work that way. They’re under full compression (internal gas pressure) when they’re at rest. All cocking the gun does is move the internal piston against the already-compressed gas that’s ready to blast it back when the sear releases it. There’s a very small amount of additional compression of the gas, but it isn’t what makes the gas spring work as well as it does. The gas spring unit is always at full potential — even at rest.
So, this gas spring unit has very little farther to go at this point…under a quarter-inch, in fact. THIS sure makes things easy for me. Pry the retainer forward on one side while starting the pin through the other. [Note: If I used a mainspring compressor, I wouldn't need to pry anything. I would just tighten the compressor until the assembly pin holes lined up, then insert the large crosspin.]
The crosspin will go in, but the hole for the rear spring retainer bolt (that large-headed bolt I removed when I disassembled the powerplant in Part 1) doesn’t line up with the hole in the spring tube. This is a problem.
Immediately, a problem becomes apparent. Look at the hole where the rear spring retainer bolt goes. It’s not lined up with the hole in the tube. There’s approximately a .080″ misalignment here. This ain’t gonna work. My first inclination is to simply elongate the hole. But when I reinstall it, there’s another problem.
There’s a gap between the plate on the spring retaining bolt and the trigger assembly. It won’t support the trigger this way!
The trigger isn’t properly supported by the plate that’s attached to the bolt. Worse, this changes the spacing between the front and rear stock screws and doesn’t allow the action to be reinstalled.
Hmmm. I’m wondering if this is exactly what Crosman (or BAM) had in mind — preclude an easy conversion with existing parts (since the same problem would exist on a normal Quest). That leaves me thinking: Can I just butt the gas spring against the original Gamo spring retainer?
If you look at the picture of the new rear spring retainer above, you’ll see that there’s a small plate that drops into the cup that retains the gas spring cylinder. The cylinder wants to butt up against a flat surface, and the Gamo retainer has a large (approx. 1/2″) hole in it. I need a metal plate to go over it. Wait a minute! I’ve got one right here in my pocket!
A perfect spacer for the new gas spring and it costs — well, about a quarter!
And, so, it gets reassembled. Believe it or not, the whole thing works.
Time to test!
I’ll run through this pretty quickly — the velocity is now up to about 964 f.p.s., which represents a muzzle energy of about 14.5 ft-lbs. Not killer, but obviously a lot better than the detuned gun. Accuracy shouldn’t be changed — or should it? Oftentimes, guys will detune their guns to make them more accurate — or to simply make them easier to shoot. That might have some merit, as I now couldn’t break 0.37 inches at the same range. Not a big difference, and I’m certainly not gonna suggest that the gas spring decreased accuracy. But I don’t think it helped.
So what’s it like to shoot?
First of all, everything anyone ever said about “thunk” vs. “sproing” is absolutely correct. The gun “wumps” with a gas spring, and you can actually feel a kick back into your shoulder. Nothing like a typical centerfire gun, although maybe something like an 1894 shooting low-velocity .38 specials might be comparable. But that’s just a guess.
Cocking the gun is another matter. Effort peaks at about 33 lbs., which isn’t all that high — except for the fact the effort before that peak is certainly a lot higher than with a normal coil spring. This is what we’d expect, of course, with the relatively constant pressure of the gas spring. It isn’t unbearable, but it does take some getting used to.
Back to a coiled steel mainspring
After about 40-50 rounds, I decided it’s time to restore the gun back to original spec. I rummage around my spring box and find a REAL low-mileage Gamo spring, and put it all back together the way God intended it. NOW, I can really get a back-to-back series of impressions.
First, the velocity did drop a smidgen. It’s now down to an average of about 943 f.p.s., or a little under 14 ft-lbs. Second, and despite the tar on the spring and rear guide, we DEFINITELY are sproinging ourselves rather energetically. Lastly, the cocking effort is predictably much milder. Peak effort is down by 5 lbs., and the effort before that peak is even easier. Accuracy is unchanged from the gas spring.
How did my quarter, er, my impromptu gas spring backing plate pan out? Not too well.
The pressure of the gas spring punched a deep divot into the quarter.
The flip side doesn’t look any better.
I flattened it back out with a hammer, and I’m really hoping it’s still legal tender. Anyway, as I sort of expected, the relatively soft quarter didn’t do well. The backing plate really ought to be steel, 0.060 inches (1.5mm or 1/16″), just like the original.
But the bigger problem wasn’t the quarter.
There’s a serious indication of metal-to-metal galling.
There was some serious metal-to-metal contact going on here between the cylinder of the gas spring and the inside of the piston. If you look at the above pictures of the quarter, you’ll see that the indent isn’t centered. The pocket in the original rear spring retainer keeps the spring cylinder right in the middle, and apparently that’s real important because it won’t center itself.
And that’s about it for now. If this is going to work, we need a simple and cost-effective way of keeping the gas spring centered properly without permanently altering the original parts…and do it in a way that the average tinkerer can accomplish on his own. The first thing that comes to mind is to drill and tap a new hole in the new rear spring retainer, opposite of and slightly forward of the existing hole. I tried that, and found (predictably) that getting the hole in just the right spot is a bit difficult without a custom drilling jig.
For now, I’m just going to give it some thought.
WAIT! I JUST GOT AN IDEA….