Colt used the "C" serial number prefix on M1911's intended for commercial sale, so its not a stretch to conclude that they would have used it on other military weapons intended for sale to the general market.Can't be 100% certain, but it looks like a very early, post WWI Colt commercial gun. Still has the same basic receiver construction as the WWI Model of 1917, but has other features that are more in line with commercial production rather than U.S. Military. The large screw for the breech lock cam, on the bottom plate, is one such example. Also, there is definitely a feedway front spacer for a caliber shorter than the original 30-06, so it may be any number of things. We know these were made in 7mm Mauser, 303 British, etc. The earliest commercial Colt marking I've seen is Model of 1919, not to be confused with the military air cooled version. They later updated the model number to 1924, but I think by then it may have had the modified bottom/side plate construction. This is definitely made shortly after WWI, assuming it to be Colt as I expect. No one else would have been able to make these, Colt holding all mfg rights following the war.
Is this gun for sale in Europe?