A fully-automatic custom AR-15-type carbine with a 12″ barrel appears as the “M4”. The lower receiver is from a SIG 516/SIG M400 while the upper most closely resembles a Mega Arms GTR-3H. It has a Geissele SMR MK16/MK8-style hybrid handguard (likely intended to make the gun resemble a Geissele URG-I-fitted M4A1 as used by USASOC), a stylized Magpul CTR stock and a SIG charging handle. The front sight is stylized Midwest Industries flip up and the rear one is a hybrid between KAC micro rear, MaTech BUIS and base MP7 rear sight. The muzzle is KAC birdcage and the grip is A2. It feeds from stylized windowed PMAGs in spite of the previous game having a proper non-stylized model. A 40 round metal magazine that holds 45 rounds and a quadstack Surefire MAG5-60 are also available.
The “14″ Carbine Shroud Barrel” attachment gives it an AR carbine plastic handguard/14.5″ stepped barrel/AR front sight with an added rail underneath and a small section of picatinny rail mounted on the right side of the gas block, essentially turning it into a pseudo-M4A1. The “Tempus High Tower 20″ Barrel” attachment gives it a KAC M5 RAS/20″ barrel/AR front sight, making it into a pseudo-M16A3 when combined with the “Demo Precision Elite Factory” stock. Pairing this barrel with an M203 automatically swaps the rail system for the classic M203 heatshield, previously its own separate attachment in MW19; this also happens on the game’s M16, which features this barrel attachment by default.
Other barrel options include the “7.5′ Tempus Firebrand”, the “Tempus Trench Pro”, which retains the same barrel and rail length and swaps the handguard for a black KeyMod one, the “419mm EXF Barrel”, a 16 inch barrel paired with an URX 3.1 inspired rail and the “11.5′ T-H4 Barrel”, which gives it a Daniel Defense Mk 18 rail and a 10.5 inch barrel, despite it being stated as longer.
In-game, it’s stated to be manufactured by the fictional Tempus Armament.
The same futuristic VLTOR/Magpul themed M4A1 Carbine from Infinite Warfare appears as the “Flatline” blueprint available for the in-game M4, named after the Epic rarity variant of the same name for the fictional “NV4” assault rifle (although not modeled after the actual variant that appears in that game). While both of the upper and lower receivers are retained, the handguard and sights are not and the muzzle, magazine, and stock are modeled after the MWII’s variant instead, albeit rethemed to better match the NV4 itself.