The 12ga had two cylindrical voids in the butt stock. I assumed that was done to reduce gun weight. The 20ga 31s with alloy receivers like Ithaca 37 20ga Ultras were very light pump guns.
The steel framed 31s and early Wingmaster 16ga guns aren't that good. It always amazes me anyone would pick those over old vintage Ithaca 37 pump guns. By old vintage I mean ribless barrels, fixed choke and 2&3/4" shell capable receiver.
I suspect the 'L' designation on alloy framed Model 31s is myth propagated by guys with Remington books and old catalogs.
