What are all types of the M-16?

Answer 1

There is the original M-16, which lack the forward assist and chrome lined chamber. The M16A1 was an improved variant of the M16, which added features such as the aforementioned chrome lined chamber and forward assist. The M16A2 featured improved construction, a three round burst limitation, different type of rear aperture which featured both windage and elevation adjustments, and a 1:7 twist of rifling (vs. the 1:12 rifling twist of the M16 and M16A1). M16A3 was never a military nomenclature: this was a product designation offered by Colt (who expected it to be accepted for use amongst select units), and was essentially the M16A2 with the full auto trigger group of the M16A1. The M16A4 is essentially an M16A2 featuring a carrying handle/rear sight aperture which can be removed to expose a MIL-STD-1913 'Picatinny' rail.

The M4 carbine, as well as the previously used CAR carbines, are also M16 variants, and there are several variations of each rifle.

The Squad Designated Marksman Rifle (SDM-R) of the US Army and the Squad Advanced Marksman Rifle (SAMR) of the United States Marine Corps are specialized semi auto only variants designed for sharpshooters at squad and platoon level. The two rifles are different from each other, and should not be considered one in the same.

The Mk. 4 Mod 0 was an M16A1 designed for the Navy UDT/SEALS, and could take a suppressor.

There is also a semi auto variant of the M16 in use by military competition shooting teams. It is visually different in that it has a chrome barrel. It also featured a free float barrel, although it uses a bracket designed to allow the standard M16A2 handguard to be used as part of this system.

Additionally, a number of variants of the M16 can be found in foreign service. Canada has manufactured the M16 under license as the C7, and the M4 as the C8, and there are multiple variations of either rifle. South Korea and Taiwan have manufactured the M16A1 under license, and each has their variations of the rifle. Some countries, such as the Philippines, have imported the M16 and have made their own modifications. Taiwan was the first country to adopt a gas piston driven M16 variant, the Type 65 rifle.