US Marines and US Army soldiers can be seen carrying M4A1 carbines.
M16A2 Rifle
M16A2 rifles are carried by US and Afghan forces in the film.
Olympic Arms K23B
LCDR Pete Duckman (Anthony Hayes), a US Navy SEAL on McMahon's staff carries a Olympic Arms K23B Tactical as his main weapon. Most likely, this is the same gun that was previously seen in Skyfall; the common denominator is that both productions sourced weapons from the same armory (Bapty & Co., U.K.)
Norinco Type 56-1
Norinco Type 56-1 rifle is carried by guards securing the American base.
Armalite AR-10SB
What appears to be a AR-10 sniper rifle is seen on a table as Special Forces soldiers load up for a mission.
Handguns
Beretta 92FS
The Beretta 92FS, standing in for the U.S. Military issued M9, is the standard sidearm carried by US forces in the film, notably by General Glen McMahon (Brad Pitt).
Machine Guns
M249 SAW Paratrooper
A paratrooper version of the M249 is seen carried by US Marines. The machine gun is seen with a paratrooper barrel and a full stock instead of the collapsible version.
Browning M2HB Heavy Machine Gun
The Browning M2HB heavy machine gun also can be seen mounted on US humvees.
M134 Minigun
The M134 Minigun is seen mounted on US Blackhawks, notably the one carrying McMahon.