Re: Primers for 300 RUM w Retumbo
A non scientific reply(as are most replies). The primer can be one of the most variable factors in loads. Any given load can shoot the same with all primers, shoot twice as good or twice as bad. Changing can literally take the MV up OR down. Cut groups in half or double or triple their size. Can raise pressures or lower them. It can raise or lower SD and ES(depending on how important you feel those 2 figures are)
And in lots of testing, Magnum does or Benchrest may or may not mean a thing. I've seen higher speeds with BR primers, lower speeds with mags, highest speeds with standards and everything in between.
I have not gone to look lately BUT I thought there was a large rifle mag benchrest offered by someone at some point. Might be worth looking into if you question the ability to ignite. While wanting what might be a BR assembled primer.
Get as close as you can, but utilize your skills as needed.