Hello all, I'm considering purchasing this 18-1/2" barrel for my 870 express. My 870 gets absolutely no use now and I'm thinking of making it a tacticool HD weapon. Remington 870 HD barrel 18.5"Cyl Bore 12ga : Barrels at GunBroker.com When reading the description, it mentions a detent ball. What exactly is this and what is its purpose? My end goal is to get an 18" barrel, Spec Ops Knoxx pistol grip stock, magazine tube extension, and side shell holder. Will this barrel pose a problem with the tube extension? Thanks in advance.