311 receiver help

[Nromani]

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

[Model24]

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

[PhilC]

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