In many scenes, M16 (AR-15/SP1) rifles is seen. Some of them appear to be genuine civilian AR-15/SP1s and aren't seen fired full-auto. Instead, M16A1s seem to be used to depict full-auto fire. That is, until the Grenada sequence, when the Recon platoon's weapons are both M16A1s and M16 rifles, possibly AR-15/SP1's converted to fire full-auto, perhaps do to a lack of enough M16A1 rifles for those scenes.
M16A1
Seen in the hands of several Recon Marines, used when a fully-automatic weapon is required early in the film, until Grenada when possibly all the weapons were converted to full-auto fire, perhaps due to a lack of M16A1s. They seem to have either older M16 lowers or possible civilian AR-15 lowers modified to fire full-auto, as noted by the lack of magazine fencing.
Fake M203 Grenade Launcher
One of the Marines has an AR-15/SP1 (or possible M16) fitted with an underslung Fake M203 Grenade Launcher made to take the place of the M203 40mm launcher. Upon close inspection, this is one of the first 'fake' M203 launchers that were made by Special Effect Unlimited, Ltd and later used by Stembridge Guns and other Hollywood Rental houses. It is not a Cobray/SWD or any other commercially available 37mm Flare Launcher. The entire launcher was custom fabricated out of Aluminum and designed to fire a special pyrotechnic charge. It is the same 'fake M203' used by Arnold Schwarzenegger in the movie Predator which is explained below. The visual differences between this custom M203 versus the 37mm Flare Launchers is:
1) Larger receiver with no cocking handle or safety.
2) There is a lever on the left side which opens the barrel for loading, both the 37mm & Real M203 unlock the barrel with a lever near the top of the mounting block.
3) The Trigger guard is larger and more square with no second safety trigger.
4) The 'ribbed' foregrip of the M203 & the Cobray 37mm Launchers utilize the real plastic sleeves used by Colt, this one has the 'ribbing' actually molded into the metal of the barrel. It's one entire piece, painted black and noticeable 'smoother' with the ribs spread farther apart. If you see wear and tear on the ribbed foregrip and there is metal underneath the paint, it's one of these fake M203s. The real or 37mm versions are plastic.
5) This is actually an 39mm tube not the smaller 37mm diameter flare launchers. But it is still not subject to the same restrictions as the M203 because of it's custom design. It can't take any standard breach load munitions of any kind and it's a smooth bore barrel.
6) The Barrel is slightly longer than both the standard M203 and Cobray CM203 (though all types have offered 'long barreled versions' for sale).
M60E1
An M60E1 is used by Recon Marine Private Johansson "The Swede", Used inside an armored vehicle by the Cubans, and seen on the helicopter that picks up the Recon men after the operation is complete.
M134 Minigun
Didnt someone say an M134 is seen in this movie?
Cuban Weapons
AKM
Gunnery Sgt. Tom Highway (Clint Eastwood) uses an AKM to teach his recruits in basic training, by shooting at them so they know the distinct sound of an AK-47 being fired at them. Several Cuban soldiers use them as well, just as Highway said they would.
Norinco Type 56
What looks like a Norinco Type 56 is seen lying next to a dead Cuban soldier. This is assumed based on the smooth reciever and front grips. The front sights aren't seen so it is hard to be sure.
DShK
A Cuban soldier is seen firing a DShK heavy machine gun at the Recon Marines. It is most likely an M60D dressed up to look like a DShK, similair to the guns in Red Dawn, as DShKs weren't too common at the time, but it isn't seen close enough to tell. The belt feeding into it does look considerably small though.