Yep, I think all, or at least most, of the 16's made in the past 30 years or so have been made on 12 ga frames. I've got a few 16's, the M37 mentioned above along with a Rem. 11-48 and several Winchester Model 12's; all are true 16 ga guns, which means they share the same size receiver as a 20 ga as opposed to a 16 built on a 12 ga receiver.

My 28 ga Beretta is built on their 20 ga frame, although Beretta offers a true 28 ga frame. Frankly, there isn't that much difference between the two, IMO, and when I bought this one I initially planed on buying the true 28 ga. However, I ran across this lightly used 686 at too good of a deal to pass up ad since there was such little difference between the two, I jumped on this one.

Around here 28 ga ammo isn't tough to find at all, walk into most any Academy, Dicks or Wal-Mart and you can buy all the 28 ga ammo ya need. In fact, the flat of 28's I've got, Winchester AA, came from Wal-Mart.