I'm aware of the old system used until about 1930 where adopted weapons were named after the year they were adopted (M1911, M1928, M1919) but the "new" system doesn't seem to follow any pattern. take the M16, were there M2 - M13s? what about a M15? the only ones that make sense are the M1, M2, M3 and M4 carbines. the M2 and M3 were just alterations to the M1 carbine. couldn't they have named it the M1A1 carbine or M1A2? does anybody know how this system works?