Need help with Crosman Nitro Venum - Few different Questions

[Jbutzi]

I have noticed a few shots going very low, and this is happening more and more.  It's not stock screws or scope mounts.  The shots are sometimes a foot low at 25 yards, so something seems wrong on the gun.  I am a newb but took it apart to see inside.  The piston seal edge appears to be a little messed up.  See picture attached.

1.Could this account for erractic velocity/accuracy?
2. While it is apart what should I replace by way of maintenance/mods, and where should I order?  I want to get a new seal at least.
3. Is there a good rebuild guide somewhere.  Could not find one.
4. Anybody have a good diagram or pictures of the trigger?  I took it apart and am not sure it is back together correctly.
5. Last, I found a plastic "U" shaped piece about 1/4" by 1/4" and don't know where it belongs.  Don't see it on gun diagram and I can't see it fitting in trigger,???
    Thanks   

[redtrucker610]

That little black piece I believe goes on the cocking arm. I don't remember exactly where though and I no longer own one to look. Since you already have it apart you should do a debur and replace the seal. I'm sure some more experienced members will chime in soon with better advice then I could give.

[Roadworthy]

The U shaped piece does indeed go on the cocking linkage.  If you look carefully I believe you'll see a notch on the linkage.  The piece will fit perfectly.
I personally prefer seals from Air Rifle Headquarters.  The proper one for your gun would be the New - Gamo Tesla Custom Piston Seal:  http://www.airrifleheadquarters.com/catalog/item/251485/2325552.htm
You need replace nothing else internally though as suggested you should do a debur and clean out all the original lube, replacing it with new.
Your gun is a member of the B19 family and I have attached some tuning information.

[Privateer]

Sounds to me that the Gas Piston is going bad.
"erractic velocity/accuracy" says all I need to know to get a new Nitro Piston.

[only1harry]

Did you grab the barrel to check for any vertical play?  Your barrel may have up/down movement to shoot that low.  Your symptoms sound like what's going on.  It will shoot dead center and next shot really low as the muzzle points down, then back on target again after you reload and cock it.  It then gradually happens more often as the barrel won't stay up in the original position.  It won't lock in position.  It was an issue with older NP springers.  Gene used to make a washer or some replacement part to fix this, which I believe someone else is making now, and I can't remember what's it's called.  Or you can call Crosman and have them send it the upgraded part so that your barrel makes a tight lock.

Moved your thread to the Crosman gate.

Harry

[Hoosier Daddy]

Does your trigger look like this?

[Jbutzi]

Thanks for all the suggestions and helps!   I am working on it!

[only1harry]

Why?  You want his trigger? 

Does your trigger look like this?

[Jbutzi]

I did get the gun (and trigger) back together again.  Now I am waiting for a new seal and will replace it and tune .  I hope the new seal makes the difference, if not I will try the piston next.

Hoosier daddy...that looks like my trigger.

Roadworthy...thanks for the rebuild guides!

[Hoosier Daddy]

Why?  You want his trigger? 

Does your trigger look like this?

No I was just trying get a point of reference to help him with his trigger question no one else acknowledged.
Thought a 3 view might help him out