Bolt Setback on 7750's?

[Black Fly]

I've read a number of comments and warnings over the years that the use of 209 primer systems in the 77/50 can result in bolt set back. I'm curious what bolt setback is and how the use of the 209 systems caused it. Anybody know of a good reference that might cover this situation in a bit more detail? Also curious if any of our members actually had it happen. Inquiring minds want to know.
Thanks
Bfly

 

[Chief 101]

I have had a 77/50 and shot maybe 100 rounds with 209 primers before I switched it back to factory stock and can honestly say that the 209 primers made my gun shoot horribly. I tried everything I had in my 50 cal arsenal including ff, fff, pyriodex rs, and 777. When I switched to factory stock parts it went into a reliable 2" group with the minnie and any of the above mentioned powders. I had no mechanical problems in the 100-+ rounds I shot and I cannot see how, I would stick to using the #11 caps that the gun was designed to use. That is my experience with 209 primers and the blued 77/50 I own. Chief aka Maxx Load