.313 bullets have to be forced through. My guess as to key-holing, barrel not square, as bullet leaves barrel, all the sudden pressure is release on one side before other & the pressure change causes bullet to tumble.
If it is a true Sheriffs/Store Keeper, or fake, only way to know for sure, send money to Colt Historical.
This gun is rough, no where near collector grade, frame & trigger guard sn same, grip about 3000 newer. Cylinder, only thing I can make out V 3. So, if I were to go to colt for letter, I would use frame/trigger guard sn.
Brian