With the Walther, when the o-ring was shot, it appeared to send shots somewhat wide left-right. I say appeared because it was a dead calm (smoke from a ciggie tumbling vertical) day and i was getting over 40mm left and right at 55. So I changed the o-ring and it appeared to be ok.
Appeared. Never proved it.
It's a tiny amount on the walther but the cocking mechanism puts pressure on the left hand side of the probe, which the o-ring takes up slack of and seals. I'd never have thought it would have the effect it appeared to have, but after that, it got changed regularly.
I haven't read all the words, but the other issue is cant & parallax error.
BFTA/NSRA County Coach
CSFTA Chairman/BFTA Rep