3 gun shotgun question

[another okie]

According to the USPSA rules, you can shoot a 20 gauge and it's still scored major. I've only been to one three gun, but everyone there was shooting 12, including me, and in reading about it it's obvious everyone is using a 12. Is it because we all have 12s to defend ourselves with, or is there some other reason, such as protecting our macho image or how the steel is calibrated?

 

[BerettaNut92]

I'm guessing like 1911s, lots of accessories and things like that for the 12s....hard to find 20ga speedloaders, sidesaddles, 10 round magtubes, bandoliers, etc....