Thread: Shotgun shooting like a solid round?

I bought an old hammer SxS shotgun at our gun show the other day.
I tested it out on a pattern board with light cowboy rounds and it went straight through cleanly like a solid slug, made a perfectly clean hole in the board.
This was at about 20 metres. I shoot further back at around 30 metres and I could hardly see any pellets on the board.
I dont know if its got an oddball choke on this thing, but its stamped on each barrel with the number 13, which im assuming is the choke size, but not sure what it actually equates to, or if this even has anything to do with the choke, but my other Belgian hammer gun is marked in millimeters for each choke.