Benjamin Trail NP problem

[Mickkk]

Hello all,

I have a Trail NP(first generation I believe) that is shooting weak, maybe half power. There's no air leak at the breech, it's got a brand new piston seal. I replaced the gas ram like 2 years ago. Could it have gone bad this soon? It's only seen about 200 shots max. This is the first break-barrel I've ever worked on, but I'm baffled and just don't know what else it could be.

Any suggestions?

[Roadworthy]

The gas spring shouldn't have died this quickly but that's not saying it couldn't.  How hard is the gun to cock now compared with before?  That's an indicator of spring strength.  If you damaged the piston seal that could cause power loss, too, but you'll have to evaluate which - spring or seal.

[Mickkk]

Thanks for the quick response. The cocking effort seems the same, but the piston seal is new and tight, with no damage. That's why I'm baffled. It pretty much has to be the gas ram, doesn't it? I mean, there's nothing else to it.

[SteveP-52]

If it still takes as much effort to cock now as it did when you installed that new gas piston, the piston isn't the problem.

You also said new and tight on the piston seal, so define "tight"?? If memory serves, it should only take 2-3 pounds of pressure to reinstall the piston with a new seal. Too tight, the piston drags when firing and might explain some of your power loss.

[Roadworthy]

What Steve said, but if you didn't smooth the rough edges, especially on the cocking slot, it's possible you damaged your new seal on installation.  It's also possible if the seal is too tight the effort of cocking only feels like the normal resistance of the gas spring cocking.  Either way I believe a teardown is in the near future.

[OleTomCat]

Piston seal too tight, not lubricated well enough.

Piston seal damaged when reinstalled.

Cocking force should be around 35#, if it is then your gas ram is fine.

[Mickkk]

If it still takes as much effort to cock now as it did when you installed that new gas piston, the piston isn't the problem.

You also said new and tight on the piston seal, so define "tight"?? If memory serves, it should only take 2-3 pounds of pressure to reinstall the piston with a new seal. Too tight, the piston drags when firing and might explain some of your power loss.

It's possible the cocking effort has dropped and I just can't tell. It's not a gun I shoot very often and I'm used to pumping MSPs.

Hard to define "tight", but the piston slid out fairly easy when I took it out of the gun. Once I replaced the seal (and applied moly paste)it required more force to reinstall. I couldn't tell you how many ft. lbs but it wasn't particularly stubborn. I was careful not to damage it on reinstall. The thing is, it's firing exactly as it was before the new seal. This is why I'm thinking it's the gas ram, but I'm just shocked that it would fail after so little use.

I just wanted to make sure there wasn't something I was overlooking. Thank you all!

[SteveP-52]

Not unheard of for a gas piston to fail that quick. Been plenty of stories here about it happening, one being mine. Umarex Throttle, ReAxis gas piston, brand new out of the box failed in less than 20 shots. If you don't shoot it that much and it's been 2 years, the seal could have failed.

[Mickkk]

Not unheard of for a gas piston to fail that quick. Been plenty of stories here about it happening, one being mine. Umarex Throttle, ReAxis gas piston, brand new out of the box failed in less than 20 shots. If you don't shoot it that much and it's been 2 years, the seal could have failed.

Well, that must be it then. Guess I was foolish to expect anything better from today's Crosman. Nonetheless, I appreciate your help, man. Thank you

[mikeyb]

When you replaced the piston seal, did you need a spring compressor to reassemble the action? If not, then your gas spring is definitely too weak. Gas springs only need about 1/4" of preload, but that preload force is around 150lbs. Not easy to do without a spring compressor.

Last time I ordered NP1 gas springs from Crosman they were ~$10.00 ea (plus $4 S&H for the whole parts order). The equivalent coil spring was ~$6.00. I always keep one or two of each on-hand for repair and experimentation. You would be surprised how many different springers can be cheaply repaired or nicely re-tuned with these inexpensive Crosman  parts.

IMO the rifle is worth repairing. Since you don't seem to shoot it much, the small amount of internal oil inside the gas spring may not be getting where it needs to be. Suggest you store the rifle muzzle-down to keep the gas spring oil puddled around the shaft seal. That should maximize the gas springs useful life.

[Mickkk]

When you replaced the piston seal, did you need a spring compressor to reassemble the action? If not, then your gas spring is definitely too weak. Gas springs only need about 1/4" of preload, but that preload force is around 150lbs. Not easy to do without a spring compressor.

Last time I ordered NP1 gas springs from Crosman they were ~$10.00 ea (plus $4 S&H for the whole parts order). The equivalent coil spring was ~$6.00. I always keep one or two of each on-hand for repair and experimentation. You would be surprised how many different springers can be cheaply repaired or nicely re-tuned with these inexpensive Crosman  parts.

IMO the rifle is worth repairing. Since you don't seem to shoot it much, the small amount of internal oil inside the gas spring may not be getting where it needs to be. Suggest you store the rifle muzzle-down to keep the gas spring oil puddled around the shaft seal. That should maximize the gas springs useful life.

Yes, I have a long clamp that I used to compress it. You're right, for 10-20 bucks it's definitely worth repairing; the gun's in great shape otherwise. And thanks for the advice on storage. That's something I hadn't considered.

[Paleoman]

I had a Benjamin regal nitro piston go bad after 250-300 shots. It became noticeably weaker and easy to cock. I had to order a new nitro piston assembly  and install it myself. Sometimes you get a lemon and have to bite the bullet and do a replacement. Normally you should get well over 1000 shots from one.