Redwolf breach O-ring not sealing .25

I am having trouble getting a good seal from the breach. Velocity is off by about 100 FPS and you can feel a puff of air at the probe if you use the single shot tray. I have tried both the stock replacement and a viton replacement in hopes that the firmer o-ring might help. Has anyone else experienced this? Is there a specific size you have had luck with? .25 cal.

Mod Edit: Moved to PCP Airguns forum
 
Make sure it’s not the mag. Advancement pin that sometimes breaks causing what you’re experiencing, it’s right under the single shot tray or mag depending on what your using, it usually sticks to the magnets on underside of tray, the pin uses bleed air from firing cycle yo actuate and is a easy fix, if it is just call AoA they will ship parts needed