I have the b-square on my super mag.It has a picatinny rail on top and mounts by replacing trigger control pins.I mounted a bsa red dot that has never moved after many 3.5 dead coyote rounds through a kicks gobblin thunder.
The B-Square is about the only mount you'll find that works the best, unless you have somebody drill/tap the receiver. I have a B-Square on my 870 with a Bushnell "Trophy" Red Dot scope, and it's been solid. One thing I did do to mount, was I took some masking tape and put on underside of mount to keep it from scratching, when mounting it, as it's snug going around receiver.
Were I inclined to scope my 870, I would drill and tap or better yet get a dedicated scope barrel and have a mount affixed to the barrel even if it extended back over the receiver. A couple of dealers I know are cussing B Square products since the move to China. I don't really know what for since I had no interest and was not a participant in the conversation, just a bystander. ??? jack