Retumbo in 6.5x300 Weatherby Mag?

[Brock]

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

 

[atek3]

youch that cartridge sounds like a barrel burner.
does it have sharp shoulder angles or the radiused "weatherby" style?

atek3

 

[Brock]

atek3,

Ya they are bbl burners but they get the job done fast lol... Between my dad and I we prolly had close to 30 of them and usually rebarrel after 1500 rounds or so... My last one had close to 3000 on it before we chucked it.. This one is blown out to a 40° shoulder and a .294 neck... Built on a P14 action with a 1 1/4" 30"shilen and a 8 twist.. I have killed groundhogs out to 1500yds with it... It weighs 25.24lbs and even at that weight it still kicks pretty dang good!!

Brock