Assault Rifle (RE3)

A shortened collapsible-buttstock variant of the M16 Assault Rifle family, chambered in 5.56x45mm, this is a standard weapon for the US Army, certain US Marine units, and the UBCS. It is also used by S.T.A.R.S. (as seen on the team photograph behind Wesker's desk in the S.T.A.R.S. office in RE2 and RE3) various police forces and many foreign military forces around the world along with the M16 itself. The M4 has a safe/semi/burst trigger group, while the M4A1 has fully automatic in place of its predecessor's burst setting. Four-position selectors with safe/semi/burst/auto positions do exist, but are extremely rare and not used on any currently-issued military M16 variants, all of which are either safe/semi/burst or safe/semi/auto, though this could still be justified as Umbrella's UBCS forces are a private army.

This weapon was carried by Carlos Oliveira during the Raccoon City Outbreak. Apparently, Carlos brought absolutely no spare ammunition for his assault rifle, which cannot be reloaded. On the Easy Difficulty, Jill can also use this rifle from the start. While the in-game model has an Optical Device (which appears to be an Aimpoint red dot sight or a Trijicon ACOG scope), a vertical foregrip, laser sight, and bipod, the FMV cutscenes reflect none of these attachments.

In Resident Evil: Degeneration, Greg Glenn, U.S. Marines, and Leon also used M4s. Greg's had his carrying handle removed and had a small rear sight in its place, while some the Marines had a red dot sight attachment. Two of the Marines had M203 Grenade Launchers, one of which Leon commandeers.

Trivia
An infinite version of the M4 can be purchased through the mercenaries minigame of Resident Evil 3.