Well not i have one but kinda took intrest from your posts . I kinda look at piston seal fit . More to too tight can cause that or starts kinda good but looses power as you shoot.

There some tx 200 rebuild vids around im sure you've looked them over .

http://usfieldtarget.com/?page_id=355

Then i guess your not the only one to struggle with that

https://www.airgunnation.com/threads/aa-tx200-mkiii-and-vortek-tuning-kit-experience.235201/

Now when i buy a spring and needed i throw in 2 or 3 extra piston seals so i have back up or extra for fitting one or if i take one down too much ( you can take off size but you cant put back on ).
 
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OP I am not sure what you indicated happened. The o-rings for the breech seals in a TX are stacked. There are 2. The port they go over and into should be a fixed solid in the compression tube. If that came out there is an issue.

 
Never seen the port tube come out o_O its position is KEY to proper breech / barrel sealing / headspacing.
ON TX's when cocked and handle is back in battery the cocking link should NOT BE loose and wiggly. There needs to be tension on the link pulling breech forward against the 0rings sealing it to the barrel.

Also CHECK while apart you can stop air from coming out by pushing down on piston while a wet finger blocks transfer exit.
Also you may find end nut on comp tube loose, or its internal o-ring failed creating a leak at the Nut/Tube interface.
 
OP I am not sure what you indicated happened. The o-rings for the breech seals in a TX are stacked. There are 2. The port they go over and into should be a fixed solid in the compression tube. If that came out there is an issue.

On that part the review By vicente .
 
Thank you for all your replies, I took the rifle apart to change the seal's piston and breech, and when I pulled the breech seals out first one came out ok with a dental pick the second o ring came out also the small metal orifice that is I looks like it is pleased into the large nut that is screwed into the piston chamber.
I have since used some lock tite and pushed it back in with new o rings left overnight and shot it with the same low fps, so that was not the problem.
I have ordered a new spring hoping that is the problem. I did push on the piston with my finger over the end of piston chamber and it held the air good. Thanks. Steve!
 
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Thank you for all your replies, I took the rifle apart to change the seal's piston and breech, and when I pulled the breech seals out first one came out ok with a dental pick the second o ring came out also the small metal orifice that is I looks like it is pleased into the large nut that is screwed into the piston chamber.
I have since used some lock tite and pushed it back in with new o rings left overnight and shot it with the same low fps, so that was not the problem.
I have ordered a new spring hoping that is the problem. I did push on the piston with my finger over the end of piston chamber and it held the air good. Thanks. Steve!
If you remove your finger and shake the tube a little, would the piston slide back out ?? If not the seal might be to tight...
 
The velocity with stock spring is 770 and with pg4ho is 777 now, I even took the spring out of my pro sport .22 and put it in my tx and the same 770 approx. but the stock spring in my pro sport gives me 700 approx which is ok strange things happening. I have checked everything all seems well.
I even put the pg4ho kit in my pro sport and all is well 700 fps. The new springs should be here Friday I ordered 2 just in case I need one again for the pro sport. Steve!
 
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I bought some of these O-rings for the breach a while back they are fantastic, Also when I store the gun I made a little rubber block that I wedgr between the cocking lever and the barrel just barley enough to keep pressure off of the breech seals.

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