The following is from a military review of the M1014 (M4). It indicates the weapon is designed to hold 6- 3 inch or 7- 2.75 inch shells in the magazine tube. Some persons have commented on being able to insert 7- 2.75 inch shells. See the following:

The characteristics of the M1014 Combat Shotgun

Manufacturer: Benelli U.S.A. Corporation.
Caliber: 12 gauge, accepts 23/4" and 3" standard and magnum loads.

Length: 39.8" w/stock extended, 34.9" collapsed.

Weight: 8.44 lbs. empty.

Safety: Ambidextrous manual cross bolt.

Magazine Capacity: Six 3" shells seven 23/4", plus one chambered round can be unloaded without cycling through the action.

Trigger Pull: 5.5 to 7.28 lbs.

Buttstock: Modular telescopic with removable pistol grip.

Sights: Adjustable aperture rear and fixed post front, radius 23.7"

Maximum Effective Range: 40 yards with 00 buckshot and in excess of 100 yards with the rifled slug.

NINE in mine.

7 in the magazine tube
1 on the lifter
1 on the chamber