Don't forget too, that if you are looking at just shotguns you might stumble on a 12ga UltraSlugHunter or a 10ga shotgun. While these are labeled SB-2, they will not fit up to centerfire barrels.
They are like "the kid under the stairs" of their receivers, along with the Versa-Pack receivers.
That NEF/H&R cares only to fit one thing or nothing at all to.
Odd it is.
-Aaron