I'm trying to develop a load for my 300 win mag, but I'm having accuracy consistency problems. I'll get a 3/8" group one day and with the same load I'll get a 1 1/2" to 2" group the next day. One day while doing an OCW test, I got 4 out of 5 bullets in a bug hole with a rather warm barrel. The next day that load was over an inch grouping.
I'm using Norma brass and have tried Winchester and Remington brass. I'm using CCI 250 LRM primers and have some Remington 9 1/2 LRM primers, which I haven't tried yet. I do have a second box of CCI primers. Since primers aren't available, I'm stuck with CCI or Remington. I've deburred the flash hole, used a primer pocket uniformer, weighed and sorted the brass, measured and sorted the bullets by bearing surface, deburred the case mouth, cleaned the brass with a sonic cleaner, I'm using a balance beam scale and double check with a digital scale. I'm using the same lot number of powders.
I'm shooting off of a stable bench with sand bags. I've thoroughly cleaned the bore with Boretech copper remover. Its a brand new match grade Benchmark barrel. The stock has been bedded, the action trued and a Timney trigger installed with about a 2 3/4 pound pull. I think that I'm not flinching.
The best results are with Nosler 180 grain accubonds with RL22 and Barnes 168 grain TTSX with IMR 4831, they just are not consistent. I've tried SAAMI spec for overall length for both bullets and loading the Barnes 70 thou off the lands and the Noslers 20 thou off the lands. I recently bought a Magnetospeed chronograph
to know what the velocities are doing. I'm getting ESs of 40 to 90 fps. Today one group was 9/16", but the ES was 30, so I know that the grouping will not be repeatable.
Anyone have any ideas on what is going on??? Or what to try???