Hadn't seen the magazine conversion for the 870, but then, I haven't been looking. I have a Winchester pump. It's a hunting shotgun, but it stays loaded with 00 Buck, and slugs, in a close closet, for home defense.
Had several combat style shotguns, years ago, sold them when I changed my career. That was a drawback for the 18" combat shotgun at the time, capacity. A magazine conversion would help, a few were tried, with mixed results. When they had feed issues, they tied up the action, that's big problem. You could always single feed in an emergency if the tube ran dry. But if the action ties up...... That's why a lot of agencies not only didn't use semi auto shot guns, but also issued 2-1/2" ammunition for 3" rated guns. You can slam a 2-1/2" shell home even in a dirty or fouled 3" chamber. A combat firearm that doesn't go "BANG!" every time you need it to can often get the wrong person killed. Hence why I haven't bought an AR style shotgun. I haven't seen a known make/model that hasn't exhibited problems. It's the only purpose for an AR platform shotgun. If I cannot count on it to go "BANG!" every time, then it isn't going into my cabinet or safe.
For the same reason, I will hone/tune the action, but I rarely use reduced rate trigger return or hammer springs in a combat firearm. Only when I know the originals are extremely over rate. Again, if it doesn't go "BANG!", or the trigger won't reset.....
