Fifty, Here goes: Rifle is a MK V with a Shilen #7 Sel Match 10 twist barrel, crowned @ 27 1/4", .338 x .378 Wby factory dimension reamer, Go gage +.001" headspace. Factory .460 stock with pillars and Steelbed. I am building it for myself.
Powders tried: H-4831, IMR 7828, H-1000, Re 25, Retumbo, H-5010, H-50 BMG.
Bullets: 180 NBT, 200 NBT, Comb Tech 200 BST, 225 BX, 250 Smkhp, 300 Smkhp.
Primers: 215 M, 9 1/2 M, CCI 250 (I didn't remember trying the CCI's).
Best combinations so far: All chrono readings Oehler 35P at 7 yds. All loads seated to mag length. < 3.8". All groups 5 shot, no cooling between shots. Cleaned between 5 shot strings.
112 gr 7828, 180 gr NBT, 9 1/2 M. 3494 fps S/D 16, group .377" horiz, .750 vert.
115 gr Re 25, 200 NBT, 215M, 3504fps, S/D 17, group .635" horiz, 1.20" vert.
Factory 225 Barnes X, 3172 fps, S/D 22, group 0.5" horiz, .690" vert.
108 gr H-5010, 300 Smkhp, 215M, 2775 fps, S/D 9, group .380" horiz, .715" vert.
H-4831, H-1000, Retumbo, didn't work with anything. 115 gr H-50 BMG had 131 extreme spread with 9 1/2 M primers. Didn't record group or S/D.
Also, 250 Smkhp's didn't work.
Looking back, the CCI's do appear to work; S/D's OK, Groups too large.
Retumbo was the only powder that ever showed pressure.
Have decided to concentrate on the 300 Smkhp. It's what I really wanted to shoot in this rifle. Looks like H-5010 has most promise, But will try H-869. My .30 x .378 likes it. 50 BMG may be too slow for 27" of barrel and full factory freebore.
I have 215 primers. Didn't use them because I thought the 215M's were just as hot but were more consistent.
I apologize for writing a book, but this rifle has the right stuff in it, and I know it will shoot 1/2 moa if I find what it wants.
Thanks for your time, information, and advice. Good hunting, Tom
Texas State Rifle Association Life Member
NRA Endowment Life Member
A big fast bullet will beat a little fast bullet every time