Firearm

Heckler & Koch HK53
In Ace Combat 4, Erusian occupation soldiers & MP's can be seen armed with Heckler & Koch HK53 carbines.

M16A1 Rifle
Sand Island Base guards can be seen armed with M16A1 rifles with A2 handguards and what seem to be 40-round magazines when the Wardog Squadron makes their escape after being branded traitors by the base commander. They open fire on the protagonists as they're making their escape in comandeered trainer jets, but are unable to score any significant hits. During the opening cutscene describing the Belkan War, soldiers fighting in the war against Belka can be seen armed with M16A1's as well.

Beretta 92F
Colonel Orson Perrault can be seen carrying a Beretta 92F as his sidearm, using it to shoot at the main characters as they run from his office after being falsely branded as traitors, but misses. Another one is used by Kei Nagase when downed, Nagase being shown holding it on one of her Yuktobanian persuers after having managed to turn the tables and capture them. She is later seen again with it when hiding from Sand Island guards prior to escaping from the base. Interestingly, when Perrualt fires his Beretta, he only fires six shots before his weapon clicks empty.

SIG SG 540
In one cutscene, Emmerian resistance fighters can be seen armed with SIG SG 540 rifles when they stop Melissa and Ludmila. One of the fighters aims his weapon at Ludmilla and is about to shoot her but is interrupted when a group of Estovakian A-10 Warthogs pass overhead, giving the women an opportunity to escape. The resistance fighter attempts to open fire on the fleeing women, but his weapon jams on him.

Browning M2HB Heavy Machine Gun
In the aforementioned cutscene, the Emmerian resistance fighters can be seen traveling in pickup trucks with Browning M2HB heavy machine guns mounted in the beds. One of the fighters attempts to engage the attacking Estovakian A-10's with one, but is ultimately killed when the truck is destroyed. It should also be noted that when the M2HB is fired at the attacking planes, the spent casings are ejected in the wrong direction and the weapon fires at a much faster rate than the real M2HB would fire.

AK-47
In Ace Combat Zero, Larry "Solo Wing Pixy" Foulke can be seen holding an AK-47 rifle while being interviewed by Brett Thompson. The rifle appears to have cloth wrapped around the handguard for unknown reasons.