Re: Accuracy with 300 Win Mag.
My buddy has a Tikka T3 300 Win Mag with the 24" barrel
I've loaded up quite a few loads for him. Probably 300 or so. There is quite a bit of freebore in this rifle. Around .100"-.200" depending on bullet(seating at mag length which is 3.365").
We have found that the 180 Hornady SSTs with H4350 shoot the best. Very comparable with H100V. I don't have the info, but I believe I was using 69 gr H4350 with 215M primers @ 3050 fps. Pretty consistent 1/2"-3/4" groups at 100. It also likes 68 gr of H100V at the same velocity. 72 gr of AA4350 provided about 3100 fps but accuracy was about 1". Tried IMR 4831 which gave 3100 fps but about 1.5 MOA.
His gun really likes 180 SSTs and Interlock BTSP. Tried Sierras, Barnes MRX, and Swift Scirroccos. For some reason it refuses to shoot the Swifts with every powder we have tried, over 2". This includes IMR 7828, RL22, AA4350, H100V, H4350, and IMR 4831.