Maybe it has a custom mag tube-76.31.5.208 00:21, 24 June 2009 (UTC) (S&Wshooter)
If I had to guess I'd say it is an extended magazine tube, allowing the spring to sit farther back in the tube to fit one more shell (since I assume the spring stops at that coiling area). My other guess was crazy and likely wrong, I was thinking it might be an H&K 512 mocked up as a Benelli M4 (since it is the only model with a similar shaped reciever and the right tube). I'm more confident in my first guess though. - Gunmaster45
IGA Coach 12 gauge shotgun
Heckler & Koch MP7A1
Mossberg 500 Shotgun
Winchester 1892 "Mare's Leg"
Tallahassee (Woody Harrelson) carries an 6 shot Winchester 1892 "Mare's Leg" with a standard lever, not the enlarged loop of other versions of the gun - .44-40.
Stainless Steel M1911A1
Tallahassee (Woody Harrelson) fires akimbo with two pistols in the shootout at the carnival. The one in his right hand is a Stainless M1911A1 Variant - 45 acp.
Satin Nickel SIG-Sauer P228
Tallahassee (Woody Harrelson) left hand gun during the fight is a Satin Nickel SIG-Sauer P228 - 9mm.