I had a venom tuning kit in my 77 and it eventually sheared the pin that holds the barrel into the tube. Barrel crept forward about 3mm.
I eventually pressed barrel back in and new pin welded in. Then a Reblue.
The venom Spring is harder to cock and loads up quite early. I ended putting a standard spring back in and the rifle shoots so much better.

Have you pushed the ball back and squirted a bit of oil in. I replaced mine, they are only a door ball catch.