However, if you are loading it while keeping your eyes on your target instead of looking down at the gun, it's very easy to stuff a round in backwards. Once you do, it's hell getting it out. If you want to use the gun immediately, plan to use it as a club, because that's all it's good for.
Do tell. ROFL BACKWARDS? I don't think I've done THAT one, yet. LOL! I used to get real ticked at my Wingmaster when it was cold and I had to leave the glove off my loading hand and my thumb was numb from the cold and I wouldn't quite get that shell in the mag when the shell elevator pinched my thumb and I yanked it out cussing and the shell would jump back under the elevator and lock up the works. Always happened when there were ducks everywhere in the sky and I was trying to get a load in fast.
I much prefer my 500's design, but it's ammo picky, too, and after shooting my Winchester autoloader or a double, I'll often forget how to pump.
Or, I'll switch from the pump to the autoloader and try to pump it after a shot, which doesn't bother the gun because it's already pumped itself. I adjust after a few shots, though. LOL
Yeah, I don't think there's a pump that could be called "reliable" when there's so many doubles and single shots out there that CANNOT jam, no way, no how, unless maybe you don't clean it in 25 years or something.
My autoloader doesn't like 7/8 ounce loads, my Mossberg doesn't like 3" Winchester high speed. They are ammo picky like your 870, just goes with the territory. Feed 'em right and work 'em right and they work. But, a good single shot or double is damned near fool proof, relatively speaking. I mean, they work 100 percent for THIS fool. Anything COULD break, but you limit the possibilities when you llmit the moving parts.