I picked up a model 12 in 16 ga not long ago. It really seems to be a natural pointer for me. The rear and front have different S/Ns, as it turns out I have a short-chambered firearm (chamber part is a 1923 model). I bought a case of 2.5 inch #5s from RST shells, ready to tee it up for squirrels in the fall. I might try a little June hunting too, as VA has a short season early June.
There is no reason with your gun to just assume that it's a short chamber gun based on the serial number of the front end. Your gun has been pieced together. Why would you assume that the barrel extension wasn't replaced? That's a much simpler change than fitting a front end to the receiver. I have a couple M-12s made up of multiple different vintage parts.
