How would i know which one it is? Who is SD&G? I do not see any proof marks. Maybe that means not Birmingham. The only thing stamped on this gun is on the frame (water table) it says Pat'd Feb 7, 1911. On the top of the barrels it says For Nitro Powder, & Superior Quality, on the bottom of the barrels is stamped "W&R". 12 Ga. 30" barrels, Serial #18192.