"But the SS 109/M855 5.56mm NATO green tip ammo is only 62 grains, which then sound only need about 1 in 10", so why did they use 1 in 7" and overstabilize the bullet? Seems like there would be no improvement in accuracy and a big loss in velocity." While it may be true that a 1/7" twist is not absolutely required to stabilize the SS 109 bullet, bear in mind that it is bullet length, not weight, which determines the twist necessary, and this bullet is a long boattail with a steel core or insert designed for pentrating body armor and helmets. It will do this better if it is spinning faster, even though a little velocity and some accuracy might be sacrificed for overstabilization!!

Keep yore powder dry!!