I have to use a 550-600 yd setting on an A3 to zero the rifle at 100 yds with cast bullets @ 1550 fps MV & the issue front sight. You'll probably have alter a front sight base to accept the Lyman globe sight. FWIW, I once bought the Lyman aperture/globe front sight for a M1903. Group sizes doubled and I suppose it was caused by the extra mass up front which disturbed barrel harmonics.