Hi any 75gr Projectile should work but in an AR two projectiles that will work and feed through the mags are the 77gr Sierra MAtchKings and the Hornady 75gr HPBT MAtch (not the A Max) Both of these projectile are specificaly designed for use in AR's with 9 twist barrels and to feed through the mag. For primers the Rem 7 1/2 primers are the best as they are the most resistant to peircing at the higher reward thrust pressures with heavy projectiles. I would get a bolt weight from David Tubb the Tungsten one would be the best and also a spring set to make sure the action does not get hammered. You can then work up from 23gr H4895 and work up to a max of 25gr ( Do not go straiget there as your rifle may not like the pressure that high) seat them to the max length of the magazene and shoot the pne that groups the best and you will be able to shoot to 1000 yards.
CHeers Bill
Australia