When they feel it necessary to do so.
Nobody. M16 is a military nomenclature specific to variants of the AR-15 rifle in 5.56x45. The rifle which the M16 was derived from - the Armalite AR-10 - was in 7.62x51 and does not have an "M" series nomenclature from the US military, as it was never adopted into service by the US military. As for civilian variants of the AR platform, there are many manufacturers - Knight's Armament, DPMS, Rock River, Bushmaster, just to name a few.
if you are going to do cqb and woodland go for the g36c, if you are just using it for woodland go with the m16
Mw3: Mp7 Silenced or Acr 6.8 Black Ops: Famas dual Mag Mw2:Acr, Model 1887, Anything with a grenade launcher Rangers Akimbo Famas, UMP, WA2000 and the last sniper (cant remember the name) CoD 5: Mp40 Round Drum CoD 4: Mp5 M16 Grenade Launcher, AK-74u.
All a matter of personal preference. However, from what I've seen in my hours of playtime, these seem to be the most common -ACR -SCAR-H -UMP45 -Intervention -M21 -FAMAS -M16 -AK-47 -L86 -RPD
A M16 cost about $2000.00
M16
The M16 was invented @ 1960
The M16 and the M4 are the US designations for the AR-15 pattern of rifles.
It has some advantages, but has yet to be proven in combat. The ambidextrous controls are a definite plus, as is the gas piston system. The quick change barrels and ability to change calibres quickly is definitely an added plus. However, unlike the Czech CZ805, it lacks a detachable magazine adapter, meaning that it can only accept STANAG 4179 magazines. The use of side mounted charging handles means it can facilitate a cheek rest on the buttstock, plus the side folding buttstock allows it to be compacted to a shorter length than the M16 or M4. The monolithic rail on the upper is a nice feature, and the use of polymers means there's less parts prone to rust. The controls are based on the M16, so familiarisation should be a fairly quick process. As far as civilian variants go, on the other hand, your money would be just as well spent on a quality AR. The "enhanced" Bushmaster ACR, with a 1 in 9 chrome-moly barrel, had an MSRP of over $3000. You could spend a lot less and get an AR built with quality parts, and even a gas piston upper system (such as the ones offered by POF, Addax Tactical, CMMG, and others), AND still have a chrome lined barrel, at whatever pitch you wanted (1 in 9, 1 in 8, 1 in 7).
Yes, along with the carbine version of the M16, the M4.
the m16 uses 5.56 caliber ammo