My guess is that it started life as a 6-1/2" barrel, and either the previous owner had it cut down and recrowned, or had a 4-5/8" barrel put on it.
Just saw a gun that got me really excited in a gun shop. Looked like an OM flat top with factory ivory grips.
Closer inspection showed it had been re-blued and not well, sported a new model barrel with factory warning, and the grips were plastic and had been artfully carved, and colored to look like old cracked ivories. It even had the correct medallion inserted. It was in a glass case, and when I asked to see it the gun shop owner warned me about it, saying it ain't what it appears to be, a real "caveat emptor".
He carefully pointed out all the anomalies, said he bought it more as a curiosity and to show people what to be careful of.