I have an AR15 that I use for PRS and want to tune my load at 600 yards. The load that I have been using for quite some time is a Hornady 75 gr. BTHP with 23.5 grain of XBR 8208 under it. I am not seeing any pressure signs but think that 23.5 is close to a maximum load. The base to ogive distance is 1.821" and the bullet jump is 0.022". The average velocity is 2862 fps (shot out of a 22", 1-7 twist, 4 groove, Bartlein barrel). The Std.Dev. on velocity is 11 fps (based on labradar data but not very high round counts (four sets of 10 shots)).
At shorter ranges the rifle shoots 0.75 moa, but I have never grouped at longer ranges. I know that accuracy really starts falling off at 900 yards but expect that I am beginning to go transonic at 800 or so. Switching to 75 ELD-M, should get me to 1000 yards but I want to burn up my BTHP bullets first.
Anyway, I was going to load 5 rounds starting at 23.0 grains and going up to 24.0 grains in 0.1 grain increments and shoot at 600 yards. I am going to look at group size as well vertical dispersion. The vertical dispersion will be compared to the muzzle velocity (which should correlate). Anything else that I ought to consider?
At shorter ranges the rifle shoots 0.75 moa, but I have never grouped at longer ranges. I know that accuracy really starts falling off at 900 yards but expect that I am beginning to go transonic at 800 or so. Switching to 75 ELD-M, should get me to 1000 yards but I want to burn up my BTHP bullets first.
Anyway, I was going to load 5 rounds starting at 23.0 grains and going up to 24.0 grains in 0.1 grain increments and shoot at 600 yards. I am going to look at group size as well vertical dispersion. The vertical dispersion will be compared to the muzzle velocity (which should correlate). Anything else that I ought to consider?