Definitely feed a bunch of different shells through that 870. Some of the newer ones have a machining mark (more of a lip really) in the action that can catch your shell and cause a pretty nasty jam. My 2015ish model 870 had that issue. A little deemed work fixes that problem up, but it’s good to know and check it out before relying on the shotgun for more important things than shooting pumpkins.
Here’s a decent little video detailing this.