us military

U.S Military officers button

Can anyone tell me about this...and doesn't it look real or a repop? The leather feels and smells old but that doesn't mean its "real"

I purchased this holster at a yard sale. What I do know is that it is government issue, has all brass hardware, the US stamp was applied on the grain side of the leather and it is stamped G&K 1918 A.G. on the back. What I do not know is what kind of gun was this for, who made it, and who likely...