I don't quite understand your statement "and with the GPR I'm aiming 6" high". Do you mean you have to aim high to compensate for drop at 100 yards? If so there is a simple fix, just file down the top of your front sight to bring the point of impact up to zero. One hundred grains of FFg will drive a .530" ball to about 1600 fps, give or take a few. At that velocity sight in 2" high at 50 and you should be no more than 2" low at 100. Or to put it another way, zero dead on at 100 and you'll be no more than 2 1/2" high at 50. Either way you can forget about bullet drop from the muzzle to 100 yards plus a few more.