with N133 powder was would max load be with a 68 graib flat base bullet.barrel is a 1 in 14 twist 6 grove hart.action is a stole.am shooting 28.2 and even with varing setinting depths it is holding .3 5 shot groups.i would like to go up 2 grains at a time.i see that some shoot 29.0 to 30.0 with this bullet.any thoughts on this .