Benjamin Trail NP Pistol. FPS is all over the place

[jungleexplorer]

I bought a brand new Benjamin Trail NP Nitro from Walmart a while back before Covid hit.  It was on clearance for $35 and I just bought it because it was too good not to buy it.  It has been sitting on the shelf for a good while because I have more important things to do.  Yesterday, I thought I would break it out and give it a try.  Fresh out of the box, I ran 20 pellets over my Chrony to see what it was doing.  I was shooting a 7.4gr lead pellet and was getting around 520 FPS on average.  It was pretty rough, so I decided to do a little break-in and put another 100 pellets through it at a target 10 meters away.  As I was shooting I noticed that the POI was dropping.  After the 100 shot break-in, I ran some more pellets over the chrony and the FPS was down around 350.  The piston chamber has hot, so I figured I would let it settle down overnight and test it again today.  I got it out and ran 20 pellets over the chrony and I am getting a 100 fps spread from 420 down to 320.

At this point the gun is useless.  It seems like a nice gun and I really enjoy shooting it, but with such unreliable performance. it is nothing more than just a toy at this point.  I know this gun has been a round for a while and am hoping some masters on here can give me some advice about it and what can be done to improve.  TIA

[7624452]

https://www.youtube.com/results?search_query=benjamin+trail+np+pistol

[jungleexplorer]

https://www.youtube.com/results?search_query=benjamin+trail+np+pistol

I am sorry, I can't read what you posted the letters are too small.

[brewbear]

https://www.youtube.com/results?search_query=benjamin+trail+np+pistol

I am sorry, I can't read what you posted the letters are too small.

I believe it was supposed to be funny.... it was the first hundred post or so...
In any case, it is a link to a YT channel.

[jungleexplorer]

I believe it was supposed to be funny.... it was the first hundred post or so...
In any case, it is a link to a YT channel.

Guess I don't understand the humor.  Kind of irritating when you ask a serious question and people highjack it to post jokes that are not even helpful. 

[Robert 5mm]

My NP pistol also was losing FPS - at that time I did not have a chrono so I do not know by how much.

I did the tissue test and I determined the lock up was not as good as it could be.
I removed the chisel lockup and cleaned out the hole and spring ( it was gunked up with original lube )
I also used a small screw set backwards inside the spring to give a little preload to the spring using the head of the screw as a spacer.
If you use too long of a screw it will not allow the chisel in to pass lockup so the screw has to be shortened.

It made for a more positive lockup and also reduced the barrel droop.
I also put a couple of drops of silicon oil into TP to lube piston seal - and let it sit pointed up for the oil to work in.

[mikeyb]

https://www.youtube.com/results?search_query=benjamin+trail+np+pistol

I am sorry, I can't read what you posted the letters are too small.

Don't think it was intended as humor(?) More likely a simple font setting leftover from another post? I bumped font to 14px so it is easier to read. Link goes to a bunch of youtube videos about the Trail NP Pistol, some of which may be helpful to you. The most likely problems to check are:

1) breech seal tissue test; will determine if breech seal or lockup is bad
2) piston seal; you need to go inside to check. Many times the piston seals are damaged (cut/nicked) during factory assembly and performance degrades as the gun breaks-in and the seal damage grow worse.
3) NP sealed gas spring is leaking and velocity is dropping.

I think maybe 2) is the problem. Sometimes seal works kinda OK and other times not, producing erratic pellet velocities
Don't think 3) because velocities would be consistently low and dropping as leak progresses.

In either case replacement piston seals from Crosman are usually cheap (~$2). The rifle NP gas springs are also relatively cheap(~$10) so I'd assume the pistol NP gas springs would be about the same cost?
Warranty service period expired? If not you may want to call Crosman.
If you decide to go inside the first thing you will need is a spring compressor.