1.172 for the SS109/M855 ball projectile. The Swedish military has measured the bullet velocities of SS109/M855 military cartridges at from the muzzle fired from differing barrel lengths. Criticism 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. The 5.56×45mm NATO standard SS109/M855 cartridge was designed for maximum performance when fired from a long barrel, as was the original 5.56 mm M193 cartridge. Experiments with longer length barrels up to resulted in no improvement or a decrease in muzzle velocities for the SS109/M855 cartridge. Shorter barrels produce a greater flash and noise signature, and the addition of a suppressor to a short barreled AR family rifle can make it unreliable, as the reduced time for the propellant to burn in the barrel and higher muzzle pressure levels at the suppressor entrance can cause faster cycling and feeding issues. Unless the gas port can be regulated or adjusted for higher pressures, suppressors for short barreled 5.56×45mm NATO firearms must be larger and heavier than models for standard length rifles to function reliably. SS109/M855 cartridges fired from barrels under about in length do not have enough muzzle velocity energy to cause extreme damage that occurs only at terminal velocities of over on impact, reducing the wounding capacity. Compared to larger calibers, proponents of the 5.56×45mm NATO round contend that animal studies of the wounding effects of the 5.56×45mm NATO round versus the 7.62×39mm have found that the 5.56×45mm NATO round is more damaging, due to the post-impact behavior of the 5.56 mm projectile resulting in greater cavitation of soft tissues. The US Army contended in 2003 that the lack of close range lethality of the 5.56×45mm