M1906 with a great bore|Winchester .22 Rim Fire|Forum|Winchester Collector

Had the occasion to take my new to me nickel trimmed M1906 Expert out for a shoot at a local dumping area. Lots of beer bottles at 50 yards. I got most of them, Grandson got the rest with his 20″ M67 Boys Rifle. Took the rifle to my friend who pulled it down and discovered something I have never seen in a M1906, and I have 10 of them. The serial number of the rifle was stamped in the stock under the tang. Anyone else seen this? Big Larry