This very sad beater of a Mosin Nagant sold recently on Gun Broker for, count it, $1085.00 + $31.00 shipping.
The rifle was rusty, dusty, and thoroughly corroded, with a chipped and banged-up stock and a very worn bore. Why did a gun in such a miserable condition fetch such a fancy price? Historical association.
Its markings revealed that it was Izhvesk Arsenal-made Model 1907 Mosin Nagant carbine cut down from a former Cossack unit Ka3-marked rifle, and it could also be identified as a Model 1916 St. Petersburg Cavalry School carbine on the basis of the metal side-attached bayonet scabbard.
Not really a true Model 1907 carbine, the Model 1916 St. Petersburg Cavalry School carbine was converted from Model 1891 rifles. These have a unique design and only the rear sight is from the 1907 model. All the parts are from Model 91 rifles, except the bayonet scabbard and the barrel bands
Mosin collectors go mad for these rarities, even in vile condition.
Note the side-mounted bayonet scabbard. It is intended to keep the point of the bayonet from stabbing the horse or the rider. One would fit the bayonet backwards onto the muzzle and then slide the tip into the metal side piece.