Hey all I could use some help... I currently have a 6.5x300 Weatherby Mag that I have been using H870 with 84-87grs behind Sierra's 142 MK.. With 84 grains im running right around 3300fps.. with 46-47 grains im close to 3500fps..But since this powder is no longer available I would like to use Retumbo instead.. However I have no idea where to start with it..

I was looking at the @ the 7STW and for powder charges for H870 and 160gr bullet is 90grs.. For Retumbo its 80.2grs Both are MAX... Now thats is about 10grains less for retumbo.. It only has Retumbo listed for 145gr bullet @ 81grs.. Since I know what max is for H870 in my 6.5x300 which is 87grs. If I take 10 grains off of that I will be at 77grs of retumbo now considering thats MAX im thinking a starting point would be about 75grains.. Am I even close on this?? Any help you can provide would be greatly appreciated..

Brock

Hey Brock - sorry to be so long out on this one - how have you been?

Your Q?: Start with 71 or 72 of Retumbo . . . expect to get to about 74 to 75 at max pressures.

If you are really in need of H-870, give me a call, I have a partial 8 pounder around and am trying my best to use something else myself..

I replied this morning over here:
https://forums.accuratereloading.com/eve/forums/a/tp.../900100024#900100024

Another choice you may try is H-5010. While some sources show it as slower than H-870, the can I had was about the same.

It should fit the rate needed, and even burn at least a tiny bit cleaner. At the time I tried it, there was plenty of H-870 around and I hadn't started having my carbon/calcium problems with 870 yet, so I didn't pursue it.

I'd have to play around a little to find my start charges, if you are interested, I'll check.