Just don't: Short version: 13-YO injures himself with a homemade shotgun.
A better headline might be "13-YO get's a first hand lesson in Newton's third law".
There is simply no need in this state for a 13-YO to make his own shotgun when there are so many proper youth opportunities available.
Right there in his home city of Buckeye there is an SCTP program. $75/yr covers everything the student needs: coaches, shotgun, shells & birds. Everything an aspiring shooter needs!
The SCTP program will explain and enforce the safety rules. Embrace and abide the rules and you will have a safe & fun time. Reject the rules and expect to be quickly ejected from the program, for everyone's safety, including your own.