Re: Ruger M77MKII 300 Win Mag with 208gr A-Max
You should be good up to around 75ish, maybe more. Hard to get too much IMR7828ssc into a 300wm case. I mean you can show pressure, but I have never managed to get so much I had problems with extraction or anything like that. Take that with a grain of salt, as the chamber on the 300 I load for is a fairly loose one, with a lot of freebore.
Just work up slowly in half grain increments, and you should be fine as long as you are paying attention.
Have a good one,