Re: Check out my 1st LR Gun - 280 AI!
I just built a similar rifle, if your barrel is 1-9, we have the EXACT same barrel.
I pretty much only use 4831sc because of similiar temps here in the Central Valley of CA. I stopped at 63 g with nosler brass and Fed 210m primers, 140 ttsx bullets, with no signs of pressure at 92 degrees and 3090 fps. I laddered 59.5 to 62.5 from 300 yards and they all came in touching (in steel) with the exception of the 60 g load jumped high about 2 inches.
In my particular rifle it seemed the more powder you put in it the smaller the groups got. The day I laddered I had a pre-determined stopping point of 63 grains (if I got there safely) and had 3 rounds loaded. After the ladder I backed up to 400 yards and in some mild mirage shot a three shot group that went about 1/4 moa vertical and a little over half moa wide, and just called it good. load is 50 off lands and 13 fps spread over three shots.
Side note: Rifle has shot 150 sst, 150 smk, and 140 ttsx under half moa at 200 yards with 59 grains.