I just took a four day tactical shotgun class at Front Sight and these are the guns I saw with failures. The worst was the Chinese made Hawk it would not stay locked in battery, a Mossberg 590 would double feed and two Mossberg 500s that would not eject the spent shell . Over half the class used Rem. 870s and had no issues . We ran 275 bird shot ,75 slugs and 175 oo buck .
I have a mossberg 500 that doesn’t like to eject the spent shell either. My favorite shotgun is the TriStar Compact for self defense. I have an 870 as well and it functions good but I have seen it double feed too.
Just as a side not too, the TriStar Compact uses Saiga mags and it seem you have to modify the mags with a bit of filing to get them to feed flawlessly too, and they advertise 2 3/4 and 3” capabilities but I found that it really only runs 3” heavy loads constantly. It seems all guns have their little niches you got to figure out
We had one person try a few drills with one of the new magazine feed 870s and it worked fine for everything except for the select a slug drill. The only way to do it was to swap mags which was a lot slower.
Maybe it’s newer Mossbergs that have problems.
I have an old one that runs perfectly and always has.
Just a thought.
Could be they were all newer guns. There was one bennelli m4 that had problems but they were caused by the operator. The 870s were a mix of new and old.