Somehow, I posted when I thought only H Richard has replied, but I now notice there were several posts including yours with the pictures, so i deleted the post so not to confuse you or the other posters. As for the barrel length, these guns came in 3 1/4", 5", and 6" barrel lengths. Without any address stampings, it is absolutely a cut barrel gun. I like the shortened barrels for shooters and conversation pieces, but they are not a "collectable" firearms.

So your gun functions in double action, but the hammer will not stay back when cocked? It most likely has a damaged hammer, which means that the "ledge" that is used to cock and hold the hammer in a ready to fire position is worn, or tampered with by a prior owner and needs to be replaced or welded and repaired. Problem is that the cost of repairs would probably exceed the value. If you want it as a functioning heirloom, the cost should not prevent you from getting it working again, but unlikely a cleaning will do the job.

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Gary
SWCA 2515