Veritas Mark IV
Gunpundit has spotted photos of the Veritas Mark IV in Denver. The Veritas Mark IV is a paintball/airgun gun that shoots .68 Caliber paintballs filled with a pepper spray type substance. The gun is patterned after and the same size as the M and accepts most AR-15 accessories.
More info about the gun here. More photos here.

The Pepperball gun fires the .68 caliber ball filled with talc mixed with OC powder. At the prison I worked in just the sight of the PB gun was usually enough to defuse any situation.