What is the difference between m4 and m16?
Very little difference. Folding stock, some fire in 3 round burst, not as accurate at longer range than M-16, Fully gas operated. I think they have changed the bolt. It is still an M16 which has been modified. I never liked the M-16's anyway. They jam too much, as does the M4.
The main difference would be the retractable stock of the M4A1, and there are many more variants of the M4.
M16 - Light Barrel, full auto, no forward assist M16A1- Light Barrel, full auto, added forward assist M16A2 - Heavy Barrel, 3 round burst, forward assist M16A3 - Heavy Barrel, Full Auto, forward assist, added flat top rail system M16A4 - Heavy Barrel, 3 round burst, forward assist, flat top rail system All versions of the M16 are around 39 long from butt stock to compensator M4 - Shortened version of the M16A4. Has 4 position collapsible buttstock, medium barrel, and is 3 round burst M4A1- Same as M4 but with a heavy barrel and is fully auto. All versions of the M4 are 33 inches with butt stock open and 29.75 inches with it collapsed. Also every branch uses the M16 and the M4 to include the USAF and Navy. The USAF hasn't used the GUU for years. Edit: Cantcu, the bolt in the M4 is exactly the same as the bolt in the M16, the only part of the inner workings they changed was a smaller buffer system.
