I have a BSA 42mm on my slug gun. I bought it just to try one, thinking the Ithaca 12 gauge Featherlight M37 would destroy it in a few rounds. That gun kicks hard.
Well, that was 5 years ago and I have killed a truckload of deer with it, including my best 8 pointer.
I'd buy another in a heartbeat, will probably get the plain jane 30mm next.
I have never had to adjust the BSA since the initial sight-in. That really counts alot on a 12 gauge pump!