In the third-tier 'dream world' the Wiseman (Scott Glenn) presents Baby Doll with her weapons, one of which is a nickel plated engraved M1911A1 pistol with spare magazines (and small jewelry attachments). In the real world, a blued M1911A1 is the primary weapon of Baby Doll (Emily Browning).
Flintlock Pistol
During the trench battle with the World War One German Zombie Soldiers, Rocket (Jena Malone) uses a combination of bayonet and single shot flintlock pistol. She uses the pistol as a club in hand to hand combat, which is probably the most practical use for the antiquated weapon in that battle. Actually as far as i know flintlock pistols are intentionally heavier so they could be used as a club.
Remington 870
In the battle with armed automatons, Sweetpea (Abbie Cornish) uses a tactical Remington 870 Shotgun with surefire light, door breaching muzzle, and Blackhawk M4 style stock.
In all of the missions in the dream, Rocket (Jena Malone) carries Heckler & Koch UMP-45 with foregrip and SureShot reflex sight. it is suppressed during the sweep into the Dragon's lair.
M4A1
An M4A1 with rails and a SureShot reflex sight is used by Sweetpea (Abbie Cornish), fitted with a suppressor during the hunt for the dragon's baby.
Unknown revolver
It was a double action revolver.
Lewis Gun
Unidentified Carbine
In what may seem like an anachronism, in a film filled with (intentional) weapon anachronisms, a zombie German World War One Soldier attacks Blondie (Vanessa Hudgens) in the trench with a rifle that has its bayonet mounted. German soldiers from WW1 would be issued the Mauser Gewehr 1898 rifle, but this is far too short to be even the anachronistic Karabiner 98k.
Modified M61 Vulcan
Unidentified Auto Cannon
On the left arm of the "Bunny Rabbit" 'Gundam' as it shoots down an attacking Bi-plane.
TBD Weapons
In the battle with the robots, who are guarding a bomb on a train heading for a city, we see heavily modified weapons which look like they may be based on real world guns.
Daewoo K3 (mocked up as FN Minimi SPW)
Blondie (Vanessa Hudgens) use a Daewoo K3 light machine gun fitted with a rail forearm and vertical grip (standing in for the FN Minimi SPW). It is recognizable as a K3 due to the shape of the gas tube and front site, visible in the second screencap below.
Short Magazine Lee-Enfield (SMLE)
As the girls walk past the British Soldiers during World War One, the British Soldiers are carrying SMLE No1. Mk III rifles - .303R
Springfield 03-A4
The Wiseman (Scott Glenn) uses an anachronistic 03A4 Sniper rifle in the trenches of World War 1, when he explains how the Germans are reanimating their dead with clockwork mechanisms and steam.
Browning M2HB
Browning M1919A4
A Browning M1919A4 is seen being chambered by Blondie (Vanessa Hudgens) in the air battle with the dragon before the dragon swallows the tail section of the plane.