Canadian Airgun Forum

I've got a Crosman Shockwave NP that started life as a <500fps rifle. I shortened the piston and it now shoots around 10.5 fpe. I suspect that the gas ram is not full power, but I have a 60kg spring on the way that should put it up around 16 fpe.

BUT... the air gun is super accurate right now shooting around 570 fps (accuracy has not been my typical springer experience). If I install the full power gas spring, is there a way to dial The power back down? Trimming some of the length from the end of the rod that goes inside the piston?

Honestly I may just leave the Crosman as is and try to sell the gas ram when it arrives. Hopefully I can tap into some experience here!

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Stoeger X3 .177, UTG 3-9x40 - 5.5 fpe
Crosman Shockwave NP .22, Hawke Airmax 4-12x40 - 16 fpe
Pumper Project .22, Centrepoint 4-16x40 - 13 fpe

One of the problems with a gas strut is that you're stuck with the power output. If you shorten the rod, the seal will bottom out in the cylinder, causing the strut to fail in short order. If your gun shoots well at 10+fpe, I'd probably leave it alone. However, if you have already purchased a full power strut, why not try it? If you don't like it, just re-install the old strut.

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Theory is when you know how something works, but it doesn't.
Practice is when something works, but you don't know why.
In my shop, Theory and Practice are combined!
Nothing works and I don't know why.

Two lathes and too many projects

You could drill a hole in the face of the piston like the Chinese do on some of the de-tuned Crosmans.

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"The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants." - Thomas Jefferson.

Shortening the nitro's rod will do almost nadda, plus you can only shorten it maybe 10mm or less. Why is too much to get into but its basically pointless. Crosman makes two nitro's for that gun that I know of, the full power (BT9M22-00-5) and low power (BT5M22-00-1) which should be inked on the nitro. fyi the last digit in those #'s can vary. I would've assumed you had the full power already, but I suppose you could have a high power that has leaked. Do you remember the shaft size at all? Any pix?
The low power is about 2/3rds as strong. I still haven't actually measured them so that's an estimate.... Imo they' both have the same pressure, but the full has a 10mm shaft and the low an 8mm which is where the power diff comes from.
Since you said 60kg I'm wondering if you bought some other brand spring? The weaker Crosman spring is ~60kg so I don't expect much to change.
I agree with ricksplace, try it and see what happens... If you get nothing from it I'd get the BT9 Crosman unit. Some people prefer the weaker spring since it is easier to cock, a smoother shooter, usually more accurate, quieter etc. Basically if you don't need the extra power there's not really any point to full power. I have one gun that has an even weaker spring and it's a great gun for general plinking, but's also 177 so velocity isn't too low. If I only had one gun I'd stay full power.
So the full power gun in 22 with a std 14.3gr pellet usually makes 700fps +-50 but it varies drastically depending on flaws. 750 or more is generally what you get after fixing said flaws or you got lucky. So 570 sounds about right for the oem weak spring, and dropping in the full power Crosman one should net ~700. Your cocking effort will go up ~50% as well.
I would not drill a hole in the piston to reduce power. It's basically the opposite of using a lighter spring, so no bennies and some things like the scope breaking reverse recoil get worse. Better to leave it full power... One thing you can do is use heavier pellets which help tame the gun and velocity. My min pellet weight for that gun in 22 is 14.3, but you have options up to the super heavy 21+gr H&N Barracuda, but I think it's better to stop at the 18.1gr JSB. The 21gr should be ~570 +-50 or more.
To get the bennies of these heavier pellets you really need a leak free gun, so absolutely no piston hole.

Well, months later and I finally got the new gas spring installed. Was shooting at 10.5fpe, now around 15fpe. 14.3’s spray in every direction, but it launches 21 grain barracudas in a nice predictable arc (570ish fps). Should make an awesome hunting rifle, but I wish it liked lighter (cheaper) pellets for plinking.

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Stoeger X3 .177, UTG 3-9x40 - 5.5 fpe
Crosman Shockwave NP .22, Hawke Airmax 4-12x40 - 16 fpe
Pumper Project .22, Centrepoint 4-16x40 - 13 fpe