When I was about twelve, things were different then; you could bring your rifle or shotgun to school if you were going to hunt after school, anyway, I made a 12 gauge pistol from an old single shot. I carved a great pistol grip and shortened the barrel to about 9 inches. I held it in a tight grip and when I fired it it flew back and knocked the wind out of me. I tried to use a stronger hold and fired it again. Same result. I took it to school and sold to some kid who thought it was neat. That was in the 40's.
You don't want a 10 gauge pistol.