Canadian Airgun Forum

In an experiment to maximize the FPS of my Crosman F11 .22 cal break-barrel, I bought some lighter pellets.

I experimented with Ruger 'Superpoint' 17gr (avg 390 FPS), Crosman 'Premier' hollow point 14.3gr (avg 441 FPS), and today I received a tin of 100 Gamo 'Luxor CU' pyramid shaped (9.9gr).

They're almost all too fat to fit. I get that some pellets fit tighter & that usually means a tight seal - but these simply do NOT fit. Checked again, .22 cal, 5.5mm, yep, but ended up not being able to push them into the chamber. A couple of them left the barrel, at REALLY slow velocity, and two got stuck (luckily I fired again & each was expelled - one at my feet!). I tried about 15 pellets in case there was a handful that didn't fit, but nope, Gamo got away with selling .25 cals in a .22 cal tin, it seems. They cost twice what the Crosman/Ruger ones did. I thought it was the painted 'brass' coloring, or maybe I'd put them in the freezer overnight to see if they'd shrink enough to use - but nope, what's left of these is going back.

Does anyone have a suggestion for sub-14gr .22 cal pellets? I'm testing the effects of the pellet weights on the muzzle velocity. I shimmed my Crosman again last night in the way that best improved the FPS, and I shot a record 151.2 m/s (496 FPS) with a 14.3gr pellet. Each shot I took after that decreased. First shot of the day: 496 FPS. 9th shot after that: 123.1 m/s (404 FPS). What is it about letting a nitro piston sit overnight that makes it so powerful, yet consecutive shots drastically decrease every time?

I'm baffled by the erratic performance of gas rams, which are meant to be steadier than springs. Sharp dives in FPS happened before shimming the rifle, but it's worse now for sure. 4mm of pre-load shouldn't turn mine into a bi-polar plinker. I could see it not benefiting too much from pre-load on a gas spring, but losing > 90 FPS after just 9 shots, at room temperature? I think I'll go back to using springs the next gun. The CDN gas ram is most definitely a toy.

The first gas rams were filled with nitrogen hens (nitro piston) but on one the rams I purchased it was tagged as 80% nitrogen, which means it is just filled with air. I am pretty confident if you take a gun from a heated house outside you will get a major swing in power if it is filled with air.

LOL, like it like it!
The temperature drop from inside to outside (20 C to -20C) is 40 degrees C which is also 40K, and the pressure ratio will the same as the absolute temperature ratio, Inside T=293K, outside T=253K so the ratio is 253/293=86%. If the gar ram is filled at room temp to 2500 psi, it will be 86% of that value at -20C, or 2150 psi. the force will drop about the same ratio. Note gas springs have a different force-displacement curve than wire spring, the force output is relatively constant over the compression stroke, the initial force to get it moving is high. See the graph attached. That said, there is very little benefit to shimming a gas ram, the increase in stored energy is negligible. For a wire spring you get some appreciable increase in the stored energy even with a small shim. (yellow line)
If you are finding the gas spring is losing power on each stroke, it's a faulty ram - likely internal leak.

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))))----//----------==
Iacio, ergo sum

Thank you, that's some great info!
Thanks to you as well, McRobert!

I did lots of experimenting, all indoors. I was advised that *some* pre-load is going to give you more FPS. I got 22-25 FPS average improvement with a 3mm shim at the base of the gas ram. I tried 4mm, 5mm, 6mm, none of which improved on the 3- 4mm shim. The placement of the shim didn't seem to matter - front of the gas ram, back by the rear chamber cap, both alone and split between both sides. Nor did any shim over 4mm. Through these tests, I was able to determine (at least in this model), what the effective pre-load is.
My tests below will also show this marked decrease in velocity as the shots wear on. I'd say about 8-10 FPS decrease after each shot. Important to note that the decrease is certain, but there are exceptions. Sometimes I'll see an increase in about 15 FPS for one shot, then subsequent shots decrease. After ten shots, we'll see about 20 fewer FPS. I take into account that no pellet is created equal. Rifle is 2 months old. There are no bleed holes in the piston. Using the stock 'BT5M22-00-1A' gas ram & the piston is properly oiled with Crosman break-barrel oil & I diesel'd it out a bit before my tests after the last lube. Gas ram is dry. The rifle sits on a workbench near a wall heater & a window, but temps aren't that warm - maybe 20C. I wonder if letting it sit allows for the piston to settle somehow - or if I should put more break-barrel oil on the piston. Do any of you add that oil in the barrel itself?

I took at least 7 consecutive shots to derive each average in these tests:

STOCK:

Avg FPS with 17gr pellet: 390 (118.775 m/s) - Max: 395 fps
Avg FPS with 14.3gr pellet: 441 (134.38 m/s) - Max: 452 fps

3mm Shim:
Placed between the Spring end of the gas ram and the anterior wall of the piston (X marks the shim): <- ( {X} [[[[[[[[[[--------- )

Avg FPS with 17gr pellet: 416 (126.86 m/s) - Max: 424 fps
Avg FPS with 14.3gr pellet: 465 (141.64 m/s) - Max: 474 fps

5mm Shim:
Placed between the Spring end of the gas ram and the rear chamber cap (X marks the shim): <- [ ---------))))))))) {X} ]

Avg FPS with 17gr pellet: 408 (124.33 m/s) - Max: 412 fps
Avg FPS with 14.3gr pellet: 461 (140.63 m/s) - Max: 472 fps


6mm Shim:
Placed between the Spring end of the gas ram and the anterior wall of the piston (X marks the shim): <- ( {X} [[[[[[[[[[--------- )

Avg FPS with 17gr pellet: 404 (123.26 m/s) - Max: 412 fps
Avg FPS with 14.3gr pellet: 460 (140.12 m/s) - Max: 472 fps


REVERTED TO 3mm Shim:
Placed between the Spring end of the gas ram and the anterior wall of the piston (X marks the shim): <- ( {X} [[[[[[[[[[--------- )
This is obviously the sweet spot for shimming this rifle. Maybe even a lower shim size would help? I never tested lower than 3mm yet.

Avg FPS with 17gr pellet: 412 (125.5 m/s) - Max: 418 fps
Avg FPS with 14.3gr pellet: 468 (142.6 m/s) - Max: 468 fps


I just got my BT9M22 replacement piston today & have been testing with it. The EBay Australian contact was a good one! Diesel'in like a WW2 tank, my god the smoke! That should subside soon anyway. A bit louder, but not bad. Kicks a *bit* harder but I can hold onto it just fine.
I'll do a full-on test of the rifle with this new piston soon, I need a day or two to work it in. Some shots are awfully slow, some are too fast to mention.
Rather than return the Gamo 9.9 gr pellets, I've decided to cherry pick the ones that fit. Still pretty pissed that > 80% of them are unuseable.

I left the 3mm shim intact while I test with the variety of pellets (17gr, 14.3gr, 9.9gr).
It's still very much in a 'break-in' mode, diesel'in like crazy, some pellets barely moving.

Max velocities so far, and remember, the first shot of the day is always the fastest:

9.9gr: *94.8 FPS (there are about 5 reasons I can't divulge that).
14.3gr: 489.5 FPS
17gr: 453 FPS

So basically, after taking a crap on Gamo, I'm still ordering more of their pellets, but a different style & even lighter. Nobody seems to sell light pellets other than Gamo. I know 9.7gr is too small for a .22 cal with any power, but I want to see how much I can get out of this sucker. Ultimately, I want to get a reliable 550 FPS out of this so when I'm PAL'd, the thing will be useful.

I still don't know why leaving the rifle to settle for a few hours gives it such a boost in velocity. I was hoping it's 100% nitrogen, otherwise why get nitro piston at all...has anyone tried a nitro piston AND a spring together?

Maybe I'll try the new gas ram without a shim - it's just so erratic - and I'm running low on ammo!

1st of all, you would not be able to even start a .25 pellet into the chamber of a .22 calibre rifle, not even the nose.
Alloy pellets, ie: the lightest made, are quite hard material, likely zinc or a zinc alloy.
As far as the workings of a gas-ram - I've no idea. I had thought the shot to shot variation, would be less than a normal springer. Guess not
or, perhaps the HW90? would be better. It surely appears so, from HardAir's testing. With the lightest alloy pellet, it ran 1,322fps @ 21.35fpe.
With a more normal 8.44gr. JSB, is was still 1,034fps @ 20.06fpe. Accuracy was listed as Very Good, whatever that means.
https://hardairmagazine.com/reviews/wei ... 7-caliber/

_________________
Best Wishes
Daryl

Thanks again, Daryl. I haven't been able to find an alloy .22 pellet yet, though I haven't scoured the internet. I looked up the HW90, that seems to be something I'll seek once I'm PAL'd. I've been dipping my toes in the gas ram market as you know, and so far I've learned a lot.

I know my quest for FPS is starting to approach forum limits, but experiences in improving the performance of my underpowered Crosman .22 cal are still within the Canadian law. If I should achieve an average FPS that exceeds that, I'll take my filthy stories elsewhere. But even with a 3mm shim & upgraded gas ram, my Crosman F11 is still shootin' within CDN restrictions. If nitro pistons are so darned consistent, then why does Crosman advertise "495 FPS" - not "up to 495 FPS". My true quest is to get what I paid for - a consistent 485fps - 495fps. Bought Crosman's lightest available .22 pellet (14.3gr) and 441 - 452 fps was the velocity range. If a gas ram can keep it within a tight 10fps range, then I'm not scared of 490 fps.

Despite my mods & shim testing & gas ram upgrade & even further testing, my fastest 14.3gr pellet was a dieseling fluke, at 496 FPS. I got a wild variety of 418 - 475 in one 30-pellet session this evening & the rifle is considerably louder. That's almost the same performance as I was getting with the old piston with a 3mm shim. I can't see how Crosman can be responsible for people exceeding FPS limits by sourcing super-light pellets or unique materials. A 14.3gr pellet is pretty light for the caliber. I was getting a stock average of 390 FPS with 17gr, 441 FPS with 14.3gr, so I'll keep modding til I get the 495 FPS I paid for. My quest is for a consistent 490-499 FPS, with a 14.3gr pellet. Even a 480-490 range would be ok. My Chrono device is a p.o.s. but I was told to get a better one & didn't listen! It likes to say "Error" a lot.

I've got one more gas ram on order. Not sure what the B5MT-22's power was - do you know? The one I have in it now (B9MT-22 replacement) gives a 60kg output. The one I have on order gives a 70kg output, so I'm hoping that's the final mod to give my F11 its promised 495 FPS (or 480-490 FPS range). I don't know what another 10kg of power translates to with the current piston. Maybe I should upgrade the piston while I'm at it. I'll click search on Crosman's site now, so in a week or so the list will appear, lol. Their Canadian site is impossibly slow.

The only diff is, though, and this is something I'll likely seek advice on, is:

The current gas ram in there now (BT9M22 replacement) is the same size as the stock BT5M22 (shaft: 110mm, body: 150mm, shaft depth: 8mm) new piston's a bit shorter (shaft: 108mm, body: 146mm, shaft depth: ???). I can easily shim the piston to fit on either end, but I want to be sure the mechanism will compress the shaft to an appropriate depth. Once I finally get the advertised 495 fps, I'll see if I can remotely get you guys a coffee or two.

Hi AS,
I have read a number of your postings and you certainly seem committed to pushing your chosen gun to the legal limit on speed. Lots of people on this forum chase different things from collecting a certain type of gun to building their own gun or accessories from scratch...
You also have mentioned that you are interested in accuracy and most would suggest that speed is well down the list of things to chase if your goal is accuracy. A pellet that shoots well in your gun is far more important than one that is a few grains lighter and 30 fps faster but groups like a shotgun. Refinement of a trigger to help you release the shot more consistently will help accuracy far more than a few extra fps.
Practice dealing with the double recoil of spring guns will help to get the pellets in the black no matter if they are launching at 400 fps or 495 (or 800).
I do not have any experience with gas ram guns so I have read some of your postings with some interest and curiosity. Good luck in chasing your gun to the limit and learning along the way.
Once you get a speed that you are happy with there are many more things to work on. Things that keep all of us tinkering and reading these forums.
Rob27

Looked online here:
www. airgunforum.ca/store/
but didn't see anything lightweight so:

www. airgunsource.ca/us/ammunition-co2/page1.html?sort=popular&brand=0&mode=grid&limit=24&sort=popular&max=150&min=0&brand=0&filter[]=22358
Within a few nanoseconds had the three following and quit looking, with others likely displayed further on.

RWS HyperMAX .22 Cal - 9.9 Grains

Predator International Predator GTO .22 Cal, 11.75gr, Lead-Free

RWS Hobby .22 Cal, 11.9gr

Uhh, you do know that they quote the max velocity using the lightest possible lead pellet they can find, probably something around 10-11gr. Anything heavier is going to go slower. Sounds like the rifle was right on the mark stock at 390fps w/ 17gr and 441fps with 14.3gr. Calculate your fpe.

Yep~ That's so true that better quality pellet helps greater in accuracy more than the little higher speed you get from a lighter pellet.

I walked the same route as OP is doing... And then I found a better diet the gun in your hand likes will be more important to push it to the limit.

And everything running at the limit and in full capacity must means it sacrifice something else, like consistency, accuracy, reliability.....

Want some more speed? Get a PAL. Forget about pushing a 450fps one to 480fps but jumping from 450fps to 900fps.

My 12fpe rifles can do 16fpe... And I run my 60fpe Impact at only 25fpe...

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~Plinkers~
FX-M3-22 Compact#PP700-Carbine#Diana48-177#XS28M-25@26fpe#HW45 Beast#AW-Custom Z-Killer DE
~Competitors~
FWB300SU#Tau-7#IZH-46M#FWB-65#CP88-C
~Target~
HW 30s/35e/97k/40+Extender/P3+Scope/70#CZ200s Laminated@10fpe#AA ProSport-177@12fpe

Here you go, 12.69gr. lead free. Buying locally is why you cannot find alloy pellets.
https://dlairgun.com/collections/22-pel ... -lead-free
11.0gr.
https://dlairgun.com/collections/22-pel ... -velocity2
9.57gr. EXPENSIVE
https://dlairgun.com/collections/22-pellets

_________________
Best Wishes
Daryl