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 Model: Bushmaster XM15 E2S A3-Type/Colt M16 A1, A2, and A4/ArmaLite M15

Nickname: M16

Caliber: .223 Remington (5.56x45mm NATO)

Operation:
Semi/Full Auto, Semi/Burst, Semi (depending on model), direct gas operated, locking bolt

Overall Length: 39.6"

Barrel Length: 20"

Weight: 7.9 lbs.

Accessories:
Colt M203 grenade launcher, Trijicon 4x ACOG scope, removable carry handle (depending on model)
There are a ton of versions of the original, full-sized AR15. The Trio, being avid gun collectors, have acquired several types—not nearly all of them but quite a lot.