The barrel length is 14", and the magazine capacity is 5+1.
The spread with 00 buck at 100 yards is about 8 feet, and at 100 feet it is about 2-3 feet. The pattern is very symmetrical, and unlike some SBS that have odd distributions of shot, the M4 does not. I have even shot #4 at 100 yards, and the symmetrical pattern is very apparent when you shoot into water. There are very few pellets that strike outside of the concentration of pellets.
The shot definitely spreads faster than my M2, even when I have the largest bore choke installed. The recoil is also very mild compared to my M2. The M2 kicks a little when I shoot the 3" magnum loads, but despite the shorter barrel, the M4 with the ARGO system definitely cycles smoother.