Originally Posted by matt goodson
When I've seen 77/97s shift its always been in the vertical plane. I've had it happen on my rifles running vmach seals, and when I've had front stock bolts in.
I now leave them out, except my 25mm in a synthetic stock which doesnt do it, perhaps because I've made the holes bigger.
The vmach seals seem to give a shift depending on temperature. Power did change, but only about 20fps, not enough to see an inch poi shift at 25 yards based purely on power. I think its the pellet exiting at a different point in the firing cycle.
Perhaps there are other causes, but I'm convinced (and have tested to my satisfaction) about these two.
Only problem is if you just use the large rear bolt is it coming loose, as happened for me this year at the Fort double header. Didnt threadlock it did I?
Plausible. I'll see what swapping some bits out does.
Mine's threadlocked, and marked up. If it moves i can see it from visual inspection. The rocket scientist has replaced the entire lug and now we just have one bolt going in. That solves the issue of the outer bolt being tight but the lug coming loose as has happened to me (still trying to work out how that happened!)