Not a steampunk cosplay laser gun
Winchester designed an anti-tank rifle in 1918. It is a bolt action chambered in .50 BMG and the grip serves as the bolt handle. The gun was patented by Edwin Pugsley and was an American take on the German T-Gewehr anti-tank rifle of the day.
Ian with Forgotten Weapons has the dish best served old on David Marshall “Carbine” Williams’ Winchester AT rifle, a completely different design of WWII vintage.