How are you getting low Standard Deviation from your magnums?

[D.Stone]

I am finally getting into reloading things that are bigger than 308 Winning-chester...namely the bigger badder and louder 300 Winning-chester Magnum.

What are you guys doing to cut down your ES/SD for your ELR rounds that you feel makes a difference?

I was doing some testing today, and just using Norma cases out of the box, and a Chargemaster, I have a SD of around 12fps. I haven't done any special brass prep like pocket informing, neck turning, or flash hole deburing.

My current plan is to use a Full Length Bushing die from RCBS, Forster BR Seater, and seat bullets closer to the lands.

I have also considered switch to a CCI BR2 Large Rifle primer; but am cautious because I would like the ammo to work well in fairly cold conditions. That is also why I have chosen H1000 powder initially .

Current load is:

300WM Norma Brass
79 grains H1000 weighed on Chargemaster
215 Berger Hybrid at 2.60 (I think it's jumping .050 or more)
CCI 250 Mag Primers

Velocity (Magnetospeed)
AVG. 2944fps.
SD. 12.3fps.

WARNING: This load is significantly over published maximums. My cartridge length is significantly longer than SAMMI maximums. Norma brass is also a lot lighter than other brands of brass.

Rifle Specs

SAKO TRG-S
Lilja Mk.13 barrel. 10 twist.
A191 Chamber
25.5 inches.

 

[Gb300wm]

My trick was to anneal my cases, load bullets 0.010" into the lands and use 0.001" neck tension.