Matthew, "Chamber Length 3" & (accepts 2-3/4" , 3" Shells or shorter shells.such as Aguila Mini Shells) : budsgunshop.com/catalog/search.php?q=aguila+mini&type=

it has a 3 inch chamber it will work just fine with 2 3/4 or 3 inch shells It will not work with the mini shells as its a 20 ga and the mini shells are only made in 12 ga see *******
UPC: 047700811451
Description: REM 870 TAC-14 20M/14CB B
Brand: Remington
Model: Model 870 Tac-14
Type: Shotgun: Pump Action
Caliber: 20 Gauge
Finish: Blue
Action: Pump Action
Stock: Black Synthetic
Sight: Bead
Barrel Length: 14
Overall Length: 26.5
Capacity: 4+1
Safety: Cross Bolt Safety
Receiver: Blue
*******Chamber: 3
Chokes: Cylinder Bore
Butt Plate: N/A
Features: Raptor Grip, Magpul M-LOK Fore-End;
NON NFA DUE TO 26.5 OAL

Matthew, this has a 3" chamber.