The 9mm is absolutely the more desirable and the best option, in my opinion. It's ammunition is available almost anywhere you try and more reasonable priced, of course. The 7.63 is an almost obsolete round now and you may well have considerable difficulties locating it as time goes by. I've fired both and, just in my opinion, I like the 9mm better in any case. If you ever find yourself wishing to sell the broomhandle, the Red 9's always sell better also. Be sure to check out the rifling in the barrels on either piece, though, as there are many of these brooms out there that have been just about worn right out. The corrosive military ammunition sometimes used had a tendency to be Very hard on barrels.