Unusual build: 300RUM, 135-gr monos

[uglychev]

This build is just something I want to try, I already have most of the components, mostly looking for powder advice.......

30" Bartlein 5r, 1-12 twist. I decided to make it a 300 RUM, and because of the slow twist, it was suggested to me to try
these 135-gr bullets:

Afterburner .308" - 135 gr | APEX OUTDOORS

.308" Caliber, 1:12" Min Twist Rate, 135 Grain, Afterburner, 50 Count

www.apex-outdoors.com

I'm pretty sure this will be a mid range laser.
I don't think the bullet will seat very deeply, probably not deeper than the body/shoulder junction.

I suspect I will need a "relatively" fast burn powder. What do you all think of starting with H4350 ? Or what else ?
I don't have QuickLoad, and do not own current times reload manuals yet, so it's hard for me to guess at a starting load point.

I thought I would start here asking the brain trust.
Thanks much Gents !

 

[6.5SH]

This will likely get you in the ballpark, but all are way slower than H4350:

https://www.barnesbullets.com/wp-content/uploads/2021/05/300-Rem-Ultra-Mag.pdf

ETA:
This online tool can give an idea on pressure IF you give it accurate data. Example; powder space is NOT case capacity to the mouth.

Internal Ballistics Manual

P-Max internal ballistics