There has been much debate of the allegedly poor performance of the bullet on target in regard to stopping power, lethality, and range. Some of this criticism has been used to advocate an intermediate-sized cartridge between the 5.56 and 7.62 NATO sizes while criticisms of poor barrier penetration, and accuracy have been used to support the M855A1 EPR round. Arguably, the criticisms about range, accuracy and lethality are related to the change in barrel length and twist between the M16 and M4. The earlier 5.56 rounds (M855/SS109 and the original M193) were optimized for a barrel with a 1:12 twist. The shorter barrel of the M4 carbine (with a 1:7 twist) generates lower muzzle velocity, reducing the likelihood that the bullet will upset (yaw, fragment, or expand) in the target and resulting in less significant wounds.