Casualties of War

The weapons seen in this movie are:

Fake Colt XM177 Commando

Sean Penn as Sgt. Tony Meserve uses a fake XM177, built up from an SP1 Carbine. What makes it weird is the unusual flash hider/muzzle brake which is too long for an XM177, the wrong diameter and has holes on one side only (the left side).

Sean Penn as Sgt. Tony Meserve carries a weird fake XM177. Here it looks to have an 11.5" barrel like an E2 model, but the receiver is an SP1 style slab side upper and SP1 style lower. It looks like an SP1 Carbine that had it's barrel chopped and a strange muzzle brake installed. At this angle, we can see the right (starboard) side of the flash hider has no holes.

Sean Penn as Sgt. Tony Meserve carries a weird fake XM177. At this angle we can see that the left (port) side has strange 'lightning cut' compensator holes in the side. The fact that the flash hider only had holes on one side makes it a very unusual muzzle brake.

Sean Penn as Sgt. Tony Meserve carries a weird fake XM177 in daylight. Here we can clearly see the strange 'diagonal' flash holes which are on one side of the muzzle brake only.

Sean Penn as Sgt. Tony Meserve fires the fake XM177. Here we can see a very strange flash coming out of the gun. After the initial flash there are no other flashes as Penn "mime fires" the carbine in 'semi automatic mode' only. Also in this night firing shot we can clearly see the strange pattern of the lopsided flash holes in this muzzle brake.

M79 grenade launcher

Used by PFC Max Eriksson(Michael J Fox). It is notoriously seen used to blow away an incoming grenade thrown at him, which in reality did happen to PFC Max Eriksson during the Vietnam War.

Type 56 AK47

Used by the VietCong's.

Mk2/M67 hand grenade?

Used to blow up PFC Max Eriksson in the Barracks Toilets.

(I cannot remember the grenade used in this scene as i havent seen this movie for some time)