Re: looks like rl25 is most popular powder?
While I 4831 isn't the best powder for the stw, it will do for moderate loads with mid weight bullets. I've used 4831 (forget which one- it was years ago) with fireforming loads in my old stw and they drove tacks, but my pops rifle hated them. Much better to go to rl22, rl25, h1000, retumbo, rl50, etc. depending on bullet weight. I'd not go to the bmg offerings unless you want to push a 175-180 grain pill.
Yes on mag. primers also.