Is it difficult to close the bolt when unloaded, or only when chambering a round? If only when chambering, I'l take a close look at the chamber and breech face. The chamber may be rough, or there may be a burr somewhere that wants to catch the shell. If it's difficult to close all the time, the problem is in the receiver, bolt, or maybe the barrel extension.
FWIW, I used to have one of the early rounded receiver versions with an 18.5" bead sighted barrel. While rather ugly, that gun was a tank and didn't give me the slightest trouble while shooting. It was also shockingly accurate with Brenneke KO slugs and fit me well, so they landed right where I pointed it. The only issue with it was that it had a bore like a gravel driveway. It seemed that, no matter the round count, you could spend all day trying to get that barrel clean; hence my suggestion to see if the chamber needs polishing.
The only reasons I no longer have that gun are that WI went to rifles for deer hunting statewide, and I inherited an 870 Wingmaster.