Midwest Gun Works is a stocking Browning Dealer, sells new Browning O.E. factory parts for most of their older models.....and new factory stocks for most models........I figured they would know about frame sizes, since they sell the new factory stocks....
Rich or Travis @ Midwest Gun Works - 636-475-7300, Pevely, Missouri....
F.N. made guns:
Rich says, the Mag 12 and the Standard 12 have the same frame...
The 16's, all of them from the very early ones clear to the end of production in 1976 have the same frame size which is smaller than the 12 frame , the Sweet 16, the Standard 16 older and newer, ...all have the same frame and will accept the same stock.......
Basically the same information Browning gave JG during his phone call.........
The 20's have a lighter frame, slightly smaller and the standard 20 requires a different stock than the Mag 20 and the 16 stocks will not fit on any 20......