The following weapons were used in the film The One:
The M4A1 is carried by LAPD officers escorting Lawless (Jet Li), the prisoner in the Anubis Universe. The rifles are fitted with the M26 MASS in addition to red dot sights and Surefire tactical flashlights.
Heckler & Koch G36K
LASERAIM Series III
A LASERAIM Series III .45 ACP pistol is the sidearm of LAPD officers escorting Lawless in Anubis Universe.
The Beretta 92FS is the sidearm for the LA Sheriff's department of Gabriel's universe.
Smith & Wesson 6906
SIG-Sauer P220 Sport (dressed up as future gun)
A SIG-Sauer P220 sport model modified. Used by MVA Agent Evan Funsch (Jason Statham) and his fellow MVA Agent Harry Roedecker (Delroy Lindo). It's most likely their universe's common sidearm for MVA agents. It had a long compensator and some odd attachment for a flashlight/laser pointer. It was more of a target symbol than a point when seen on a target.
In the movie - they had to give it an alternate name. It's called the M590.
Funsch (Statham) also briefly used an even more customized version of the gun at the end of the movie. He states directly, "My own design. Highly Modified M590 Hand-portable system. Fires 25 smart rounds per second. Multiple tracking modes plus the latest countermeasures. Each round carries an explosive anti-personnel warhead with selectable fuse delays. Tracks. Enters. Pauses .1 microseconds. Then boom, Mixto Rojo."
Sphinx AT 380 pistol
When his Custom Modified M590 was destroyed, Funsch changes to a backup pistol. He called it the "Little Brother" of his Modified M590. So it can probably be surmised that it has similar capabilities as the larger version, such as the ammo type and tracking modes.
Heckler & Koch USP Match
The handgun of Yulaw (Jet Li) seen early in the movie, but was taken away when he was caught. It is customized like the SIGs used in the movie most likely because it came from the same universe.
Seen in use by the guards of the MVA's universe. Yulaw stole one from a guard during his escape. He loses it later in the movie.
M26 MASS (Modular Accessory Shotgun System)
The M26 Modular Accessory Shotgun System are mounted under the M4A1 carbines carried by LAPD officers that escort Lawless in the Anubis Universe. The MASS in this film is the early version as later production models are slightly different.
Heckler & Koch FABARM
A Heckler & Koch FABARM shotgun is seen used by the LA Sheriff's Department of Gabriel's universe. One is seen bent by Gabriel.
Heckler & Koch MP5
Seen in use by security forces of the MVA's universe. These are kinda weird to tell what it is since it is heavily customized with a chrome barrel extending at the end and some of them had skeleton stocks like the H&K UMP's. The skeleton stock isn't the MP5k PDW folding stock. On other pictures - the stock seemed very similar to G36s but designed to be a non-folding stock.