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.