The Delta operators mainly wield the M723 and M733 variants of the Colt Commando. Staff Sgt. Daniel Busch (Richard Tyson) is the first Delta member on screen, and also the first soldier we see carrying an M723. All Delta members carry M723s and M733s, fitted with various accessories such as Aimpoint scopes and tactical flashlights, some of them also have M4 style barrels. Master Sgt. Gary Gordon (Nikolaj Coster Waldau) can be seen carrying an M733 featuring a camouflage paint scheme and a sound suppressor, which is then used by Chief Warrant Officer Michael Durant (Ron Eldard) to pick off several more Somalis before running out of ammunition and being overwhelmed.
Delta Customs
The Deltas arm themselves differently from the Rangers by using customized Colt Model 723 and 733 rifles as opposed to longer, heavier M16A2 rifles. Many are fitted with such accessories as Aimpoint scopes, tactical flashlights (with the activaters duct taped to the foregrips), some of them have camouflauge paint schemes, and some of them are fitted with longer, M4 style barrels for better accuracy.
Rangers
While the Rangers are armed almost entirely with M16A2 rifles, Cpt. Steele (Jason Isaacs) uses an M733 rifle noted by the 11.5" barrel, with nothing modified or changed. A field medic is also seen using an M733, presumabley because he would need a lighter, more versatile weapon to move quickly to wounded soldiers.
Delta Sniper
Master Sgt. Gary Gordon uses an M723 rifle with the camo paint, scope and lasers, but his is fitted with a sound suppressor. Shughart gives his rifle to the wounded Chief Warrant Officer Michael Durant, who uses it before it runs out of ammo.
XM177E2
Some of the Deltas are seen using Colt Commando XM177E2 A2 rifles with the original long type muzzle break, which are also heavily customized.
Those have A2 receivers, like the ones in Blood Diamond (which was, ironically, done by the same armorers as this film), so they're not XM177E2s. I don't know what those are called; probably just something thrown together from a mix of parts.
M60E1
Specialist Shawn Nelson (Ewen Bremner) can be seen carrying an M60E1 machine gun as his standard weapon. Some of the Somalians can be seen using them as well.
Note: The original M60 machine gun was pretty much obsolete by the end of the Vietnam war. The M60E1 is an improved varient far more common in films.
FN Minimi
Several Rangers can be seen carrying FN Minimis throughout the film, standing in for the M249 SAW (note the lack of heat shield over the top of the barrel, frame-style stock, and 90-degree carry handle). It is also the weapon used by Specialist Lance Twombly (Tom Hardy) to accidentally deafen Nelson when he fires it too close to his head. A lucky shot from a Somali also causes Twombly's extra ammo to ignite, nearly setting him on fire.
M16A2
Staff Sgt. Matt Eversmann (Josh Hartnett) leads his Rangers armed, like most of them, with an M16A2s.
M14
The M14 Rifle is seen being used by Sergeant First Class Randy Shughart (Johnny Strong), most notably when he and Master Sgt. Gary Gordon are covering the second crash site. His M14 sports a camouflage paint scheme and an M68 Aimpoint scope.
Heckler & Koch G3A3
The local militia arm themselves with, among many other weapons, H&K G3 assault rifles.
PKM
An PKM light machine gun is seen resting on a table in the Somalian arms dealer's shop.
RPK
One of the Somalian fires on Mike Durant's Black Hawk armed with an RPK light machine gun. Its blonde furniture indicates it could be a foreign copy. The machining divots in the reciever could indicate something too.
RPG-7
The Russian manufactured RPG-7 features prominently in the film as it is the weapon which brings down a pair of Black Hawks. In one scene, a projectile from an RPG-7 strikes the driver of one of the deuce and a half trucks in Lt. Colonel Danny McKnight (Tom Sizemore)'s convoy and fails to detonate, impaling the luckless soldier instead.
Norinco Type 56
A full stock Norinco Type 56 is used by a Somalian to whack Mike Durant in the head. It has a slanted AKM syle muzzle break, meaning it was a Chinese import. The muzzle break was added by the importers before sending it to the US for filming.
Norinco Type 56-1
Nearly all of the Somali gunmen are armed with the Norinco Type 56-1 assault rifle, which is a Chinese derivative of the AKS-47/AKMS. They are identified by the hooded front sights, which only Chinese Kalashnikov rifles have.
AKS-74U
Razaaq Adoti as the Somali militia leader Mo'alim carries an AKS-74U as his weapon of choice, first seen picking it up and inspecting it before heading into battle, then firing a burst into the air to break up the mob attacking one of the surviving Blackhawk pilots before announcing that he was to be taken alive as a prisoner.
SPG-9 Recoilless Rifle
At one point in the film, Somalis begin to bombard the building the majority of the Rangers and Deltas have taken cover in with mortars and a SPG-9 recoilless rifle. A group of Deltas soon kill the gunners and then turn the weapon against the Somalis, killing several with one shot before destroying the weapon with a thermite grenade.
While the Colt Flare Launcher is fitted on most of the Ranger's M16A2 rifles, a couple of actual M203 grenade launchers attached to M16A2s are seen, the most notable of which is Specialist John Grimes (Ewan McGregor) who assists Delta in taking out a technical that has them pinned down, missing the first shot before destroying the vehicle with a High-Explosive Dual-Purpose (HEDP) grenade from his M203.
M1911A1
We see the M1911A1 pistol in the hands of the Delta operators as their sidearm of choice. As the two Delta snipers attempt to secure the second crash site they are forced to draw their M1911A1 pistols as the overwhelming Somali forces close in on them. Another Delta operator can be seen practicing with an M1911A1 near the beginning of the film.
Norinco Type 54
A Somali militiaman uses a Norinco Type 54, noted by its frame mountd safety switch, to kill SFC Shughart (Johnny Strong) at the second crash site.
Beretta M9
The Beretta M9 pistol is seen a few times in the film in the hands of Rangers, and members of McKnight's convoy. Mainly it is seen in the hands of Maddox in the Humvee. McKnight himself carries his M9 sidearm around as a proper means to defend himself.
Heckler & Koch MP5A3
Chief Warrant Officer Michael Durant, a Black Hawk pilot, is armed with an H&K MP5A3 and uses it to defend himself after he's shot down.
Browning M2
The Browning M2 heavy machine gun is fielded by both the US Army HMMWVs, the UN APCs, and the Somali militia in the film. The opening shots of the film feature Somali militiamen slaughtering a gathered crowd at a food distribution center with the powerful fifty-cal.
GE M134 Minigun
During the slaughter of the crowd, The U.S. forces hovering in the MH-60 aren't cleared to fire the GE M134 Miniguns mounted on their Black Hawk. Pylon-mounted miniguns are also carried by the AH-6 Little Birds and rain lead in several scenes.
DShK Heavy Machine Gun
Several vehicle mounted Russian DShK heavy machine guns appear in several scenes of the film.
M72 LAW
An Army Ranger, Lieutenant Tom DiTomasso, can be seen taking out a "technical" with an M72A3. The M72A3 was a Post Vietnam improved model of the M72 Rocket, and the last variation used by the U.S. Army. Upgrade versions (up to M72A7) of the LAW are being fielded by the U.S. Navy and USMC as recently as 2007.
Remington 870
While never used on screen, Sgt. Sanderson (William Fichtner) can be seen with a customized Remington 870 Express Magnum slung over his right shoulder. A pistol grip with a folding stock is used in place of the full stock. For some reason, he didn't shorten the barrel, which would have made it more versatile.
M67 Hand Grenade
While loading up for the assault on the Olympic Hotel Sanderson (William Fichtner) picks up M67 fragmentation hand grenades. He is also seen throwing one into a window to take out a Somali who has him and the Deltas and Rangers pinned down.
M7A2 Hand Grenade
An M7A2 CS gas grenade is seen sitting next to the M67 fragmentation hand grenades Sanderson picks up.