I just got a new 18.5 in barrel for my 870 (Mossberg made for an 870), but the slide will not slide all the way up (and the bolt doesn't fully engage). There's about a 1/4" of travel left on the slide and the bolt is almost in position. The new barrel looks identical to the old one and it worked fine. I can't see anything problem and the internal alignment looks to be identical to the old barrel. Does anyone have any ideas?
My guess is a bad barrel. I just can not think of anything you could be doing wrong. Bring the barrel back to where you bought it. If you wanted to you could remove the bolt and try it to see if it is the lock-up(bolt) or the forearm hitting.
Just walking on the edge of of my grave.