Any 870 barrel would fit, but why not go with the 12.5.
If I had to guess it might have something to do with the fact that on a 12.5" with a pistol grip, it drops below the OAL requirements.
Bingo, got a grizzly with a folding stock, no barrel, on a trade and I am looking at getting a new barrel for it while retaining the folding stock.




























