I get pressure signs using 42.5 of 4064 using FGMM cases in my bolt gun, that's running an OAL of 2.9". I'm also getting 2640 for velocity with 42.1gr from a 24" barrel. 43 seems too hot.Federal Gold Medal Match 175's are the standard for long range in an M14 style rifle. They use 43 grains of 4064, with a muzzle velocity of 2600 fps.
I consider that to be the top end for an M14 style rifle. I use a Schuster overbored/ported gas plug to save wear and tear on my oprod.
Federal uses the same load with the 168 grain version, but the velocity comes out a little higher at 2650.
Also, if I remember correctly, the 175 FGMM load is 41.7 of 4064 using FC brass.