Came in a box of reloading supplies from a friend.  He said it had never been shot.  Won't stay cocked and the trigger won't reset.  What's with the line in the barrel through the serial number?

Was this a kit gun?

Have not disassembled it yet.  Still going through the boxes of 30 year old reloading supplies.

That is a Spanish made Philadelphia Derringer, probably .45 caliber. They were sold in kit form in the 70's and 80's. I thought it was a CVA at first but it's not marked so. There was another company back then that imported these and I can't remember their name but I have a Kentucky pistol from them. The line in the sn is definitely where the breach screws into the barrel. A good cleaning may be all the lock needs but someone probably botched the sear cut trying to make it a "hair trigger" as that was all the rage back then. You can probably either recut and reharden the part or find a replacement on ebay Or Dixie Gun Works.
It appears to be a kit gun based on the quality of the build.
If you get it working it will take a .440 round ball with a patch and about 20-25 gr of powder. 2f or 3f would be ok.