In principle, I'd agree there's nothing wrong with making FA guns R instead of P.
In practice... I fired FA guns in my Reserve days, and the thrill wore off fast. Maybe I'm just older and wiser [tired and jaded] but I think this is one of those things that seem fascinating but nobody would bother with for long. I could see firing off a mag or two just for the experience, but I wouldn't spend a nickel to have one for myself.