Big 338 powders??

[lovdasnow]

Hey guys my 338 Rouge(338-378 improved) is getting finished up, and I need to get a few powders to start load workups.

will be shooting 300gr bullets. I like RL25, but would like more temp stability then it has.

what should my choices be? H-1000, Retumbo? anything else?

thanks again,

[Long Time Long Ranger]

Retumbo getting close and you can get some good loads with it but the others are way to fast for this cartridge with 300's. You will not get top velocity with powders faster than Retumbo. Look at a powder chart and pick out the slowest ones on there. If you can find any H-870 it is very good. H-50BMG, H5010 and the slowest Vihtavuori powders from 170 and slower. I haven't tried US 869 but it may work.

[lovdasnow]

great, thanks. are those powders you listed pretty temp stable?

[backwoods83]

retumbo is probably the most stable of the powders mentioned, this might sound insane but with the pressures that case will hold id start with some tame loads of imr 4831 and work up 1 grain at a time, velocity may slighly suffer, but you cant beat consistency! want more speed RE22 or imr 7828ssc. good luck!

[BountyHunter]

MRP2 is same burn rate as RL 25, but lot more stable. I have used it in the 338 AI quite well.

BH

[Long Time Long Ranger]

lovdasnow, I currently have seven 338-378 weatherby's I built when it was a wildcat well before it became a standard cartridge. My data on the 338-378 wby alone would make a good book. I have extensive data with most reasonable powders on bullets from 185-325 grains shot on my range. Powders faster than retumbo limit the velocities attainable with this cartridge. Send me a PM and I will get you some data. Yours would shoot the same powders best just more of it with better velocities. I am not familiar with your improved version but the 338-378 wby imp is certainly at the top of the big 338 spectrum. This huge case having the ability to utilize massive doses of super slow burning powders is what puts it well ahead of the various offerings off the ultramag and lapua cases.

[HighKnob]

Weidner's has WC 867 and 872, new military powder for $49 for 8 pounds. I've read some good reports using it in mag calibers with heavy bullets. Been thinking about trying some in my 7 mag, but it's on the low end of this powder with 140 gr. bullets. It's slow and very stable from all I've read.