311 receiver help

Good evening. Newish member here and new to sxs shotguns so please go easy on me. I recently bought a Stevens 311a (what I thought was a 12g) receiver on GunBroker per the listing. Found some 12g barrels for cheap and got them put on only to find out they stick out about 1/16th of an inch on either side. I am wondering if this is because it is a 16g+ frame? Or is this sort of tolerance normal? Is there any place to find out what the receiver dimensions are for a 12gauge from say 'ear to ear'? They snap right in and open and close perfectly. If this is the issue I now have a pair of 12g barrels in very nice shape I'll be looking to swap for 16g. Thanks for reading.

https://imgur.com/gallery/oZM6DrT

I measured my Eastern Arms 16 GA (Sears version). 2.14 across the receiver at the breech, 2.12 across the barrels.

My 311 (sold by Sears) in 12ga measures, by caliper, 2.232" and barrels are flush to the receiver.