I think the 28 suffers for some of the same reasons the 16 does (I love my 16's! They're old.). It's built on the next gauge up frame these days.
I'm pretty sure the BPS is a 20 ga frame, as is the Model 12. This makes the gun heavier, which plain sucks.
Like Steave said, I'd rather shoot the 20...

Now that Franchi 48AL would be a treat! But talk about making expensive empty hulls in a hurry!!

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War Eagle! '10 BCS & '13 SEC

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.