I wonder why the markings look like the letters were individually stamped? I would think a gun maker with the experience of Charles H. Rigdon who was also involved with the Leech and Rigdon revolver prior to the war would never use such a method.
I also wonder about the OP calling it a .44 caliber? All of the Rigdon and Ansley pistols were .36 caliber copies of the Colt 1851 belt pistol. .44 caliber revolvers of this size used a rebated or stepped cylinder and the cylinder on this gun looks like it is straight, not stepped like the .44 caliber pistols are. If it really is a .44 caliber revolver it is a fake.
The 12 cylinder stops was a method of providing a safety that used the notches rather than the "safety pins" that Colt used. It was first used by Manhattan Arms in 1859. Not all of the R & A pistols used it.
The serial numbers should be marked on the bottom of the barrel lug below the loading lever, next to the trigger guard. The guns frame right next to it should also have the same serial number as should the trigger guard right behind the front trigger guard screw. In other words, there should be three serial numbers right next to one another.
Flayderman's Guide said in 2007 a Rigdon Ansley revolver in fair condition was worth $17,500 with a very good condition pistol valued at $45,000. If this gun is a real Rigdon and Ansley it should never be shot with any load.