The prison guards U.S. Marshals and DEA agents arm themselves with SIG-Sauer P226 handguns. The convicts use several P226s captured from the guards, most notabley Cyrus "The Virus" Grissom (John Malkovich), who steals the co-pilot's SIG-Sauer from him after he removed it from the lock box.
The cons take several M16A3 assault rifles from the weapons stash. While they could be M16A3s, the the full auto version of the M16A2, they are most likely M16A2 upper recievers, placed on full-auto lower recievers, or genuine M16A2s with drop in full-auto auto sears.
When Cyrus throws down his empty M16A3, it changes to a rubber prop featturing the M16A2 style sights but lacking a forward assist and shell deflector.
When Cyrus takes the guns out of the weapons hold, a few of the cons use mocked up grenade launchers made to mimic the function of an M79 grenade launcher. Based on what is visible, it looks like a break open tube with a Smith & Wesson Model 15 revolver inside (note the hammer and double action function) the grip with a Smith & Wesson 4506 trigger guard. It is fitted with a wooden stock with a similair shape to an M79 as well.
I'm pretty sure it's not a mock-up. I've seen grenade launchers like that before. As I said before the edits, they also appear in Predator 2. I can't remember the manufacturer, just that they are real and not something made up for the film.
One of the Cartel members uses an unknown pistol with an extended barrel to thread a suppressor and target style grips. Cameron Poe (Nicholas Cage) comment that the cons would hear the shot, so he threads a suppressor on it. When Poe disspatches all the Cartel members, he takes the gun for his own use, before dropping it diving from an explosion. It actually resembles the LWS-32 from earlier in the film and could be a SD model or something. It also looks a bit like a Colt Woodsman pistol.
