Throating opinions for 300 rum.....208-230 Bergers

[Dshooter]

Looking for opinions from experienced RUM experimenters...lol. It's a total custom with a stiller tac300 and a Brux 1:10 straight(almost) contour barrel 30". I plan on really only shooting 208amax, 215 & 230 hybrids. Need some advice on where to set the lands. My ideas for max case capacity in case I needed it, put the amaxs at 3.92 OAL and the 230 at around 4.00. Not sure what SAAMI chamber specs are but I'm sure they are gonna be to short for me. Thinking these bullets will be fine at .020-.040 off lands. Hope all this makes sense to all because it does in my head

 

[Apothus]

My rifle is a straight from the factory Sendero 300 RUM. When I seated the bullets way out, they touched the lands at 3.850. I backed off 20 thou and found my happy place with the 230gr Bergers at 2825ish in this cold weather.

SAAMI in case you're wondering is some rediculously short number, 3.6something I believe. The manual is in the garage

 

[Dshooter]

Thanks for the reply. This is the info I was hoping to start hearing. My buddy strected 180 sciroccos out and hit the lands at 3.799. Now I can set a berger 230 in a case at your 3.85 and see where the ogive is on factory chamber and adjust from there. I knew that SAAMI mag specs was 3.600, I was wondering more about actual chamber spec. When I measured the other day to have full neck engagement on a 230 hybrid, the OAL was around 4 in even. I just want the ability to run more powder if needed, do to the fact that I want to push the 230 out around the 2950-3000 mark. Thanks again for info and keep it coming guys!

My rifle is a straight from the factory Sendero 300 RUM. When I seated the bullets way out, they touched the lands at 3.850. I backed off 20 thou and found my happy place with the 230gr Bergers at 2825ish in this cold weather.

SAAMI in case you're wondering is some rediculously short number, 3.6something I believe. The manual is in the garage

 

[Apothus]

Thanks for the reply. This is the info I was hoping to start hearing. My buddy strected 180 sciroccos out and hit the lands at 3.799. Now I can set a berger 230 in a case at your 3.85 and see where the ogive is on factory chamber and adjust from there. I knew that SAAMI mag specs was 3.600, I was wondering more about actual chamber spec. When I measured the other day to have full neck engagement on a 230 hybrid, the OAL was around 4 in even. I just want the ability to run more powder if needed, do to the fact that I want to push the 230 out around the 2950-3000 mark. Thanks again for info and keep it coming guys!

I'm using RL-25 powder, which is harder to find than brass right now, and I'm getting 2825fps average out of a 26 inch barrel using 81.8 grains of powder. The Berger manual states for every inch of barrel you gain ~32 fps. So 32x4=128+2825= 2953 FPS give or take plus variance for crappy in-my-head math. You should be right on your goal using my example, and if you can find a slower powder like Retumbo or H1000(ha, good luck) you'll be golden.

 

[Dshooter]

Yeah I do have Retumbo and US 869. I think I'm going to end up throating this barrel about .100 longer than factory. That still allows me to seat 208 amaxes safely at the same distance off the lands as the 230 Bergers. If needed be, I'll have more than enough case capacity to load 230s as hot as needed but still be well within the case neck. Your velocity to barrel length is spot on.