The Ottoman Empire purchased a staggering number of Mauser rifles over many decades, and Turkey would update many of them to a standardized pattern in the 1930s. This particular example is very rare, with an attached folding bayonet.
The base rifle here is (was) a 1903 model Mauser carbine, chambered for the 7.65mm Mauser cartridge. Starting in 1930, these were updated to chamber 8mm Mauser ammunition, given longer barrels, and in this case, that folding bayonet. We can see evidence of the gun’s past in the receiver notch necessary for the longer 8mm cartridge, and the residual Turkish numbers, which predate the transition to Arabic numerals in 1928/29.
This rifle is part of Lot 794 at Rock Island on Thursday, October 8th.