Crosman Vantage NP piston seal

[Ultramarine]

I hadn't shot my Crosman Vantage NP for a while and I got puzzled by how poor I got punching paper targets. So I set a chronograph on its muzzle and found I got 667fps instead of the usual average 870fps speed I can usually expect with a 8.64 gr pellet. Moreover, I got quite significant differences in speed between shots.
As I can't feel the riffle to be easier to cock than before (I know I'm getting older, but not that fast!), I suppose my piston seal is worn out.
So my question is : can anyone tell me what's the exact reference for this seal ? As I'm in Europe  finding Crosman airguns spare parts isn't so easy but I still can hope...
BTW I opened the Crosman Vantage NP diagram on Crosman site and found the piston seal (N°1 part!) but couldn't find its specifications.

[Roadworthy]

What specifications do you seek?  I believe the compression tube on that one is just over 25 mm but way short of 26 mm.  The piston seal for a TX 200 will work but should be taken down a wee bit in diameter.  I get my seals from Air Rifle Headquarters in Maryland in the US.  You can get seals from England via https://www.airrifletuning.com/ in the UK.

[Ultramarine]

Thanks a lot Thomas.

I'll send them an e-mail to check whether they can provide such a seal or not.
I found an eastern Europe reseller on e-bay who says the piston seals he sells matches a Crosman Vantage NP piston but he mentions an "ancient" type of seal and I don't see what he means.
Any idea on your side ?

Kind regards,
Yves

[happymecanic]

I hadn't shot my Crosman Vantage NP for a while ...

Hi Yves. Since your rifle has been sitting for a while, the breech seal may also be crushed by the long storing-in-the-closed-position time. I suggest you do the tissue test over the breech, it cost nothing and will tell you if that seal may also be in cause. I had this issue on my Trail NP, I just fixed it by making a shim out of a soda plastic bottle. I think it was 0.007'' thick, 0.17-0.18 mm for you  .

[Ultramarine]

Thanks for your answer.
A while means a lot of things and I have to admit it wasn't a long while since I hadn't shot this rifle, I mean a week or two .
But I paid a particular attention to what you tell me because the last time I had such an issue with this air rifle, It happened to come from the breech seal, which went (too) flat. So I put a piece of dental floss to make it protruding better and may be I'm going to do the same . I got my whole family coming home this week end (11 persons!) so I'll wait for Tuesday before making a sealing test. I usually use talc powder which, besides the possible testimony of an actual leak, offers a funny " black powder" style shot.

[mafatone]

I own one  of these. Very accurate with a good pellet.

[Ultramarine]

Now this is really getting weird!
I first tried the "talc powder test" which I consider more accurate than the tissue one. No white cloud, not even a small one and I had to wipe the powder off the breech after I shot. So there can't be any significant leak between the breech and the barrel and the seal must be OK.
Then I measured a 8.64 gr pellet speed in a 12 shots serial with my Chinese chronometer, which I consider quite accurate. I could read 714, 689, 689, 682, 669, 673, 669, 663, 663, 663, 666, 663, 663.
So I bet I must get prepared to a gas ram and piston disassembly. Did I mention all the screws are duly tightened and prevented from moving  with some "middle strength" Loctite thread locker ?
Now I beg a piece of advice from the good fellows and experts at GTA : is there something to guess from the speed numbers I mentioned above? Should I expect a seal or a gas ram change (or both )?

[ER00z]

It's possible the gas ram is going flat or losing pressure. It's rare, but possible. The piston seals can last for many shots. Usually the piston will slam violently if bad piston seal. But having a spare is always good. Don't know of current availability for parts, but many 25mm seals should be available. I believe the Gamo 25mm seals work also. Custom Air seals of Australia has them listed together.

You should start with the gas ram if it got easier to break the barrel and cock. Crosman may be able to supply a new gas ram. Not sure of shipping to your area or if in stock. A good spring compressor is highly advised for working safely on airguns. If the gas ram goes completely  flat, you may not need a compressor to remove, but better to be safe. You will need one to reassemble. Even if lower pressure is present in gas ram, it may still be dangerous to disassemble!  Be safe.

Best of luck to you. Take it easy.