9x19 or 9x21 in P9

Gillster Aug 26 2004, 12:10 AM I picked up a P9 set up for open for my 13 year old son to shoot steel type matches with. He wants to try USPSA now as well. The gun is a blast to shoot but so far we have only used minor loads. The gun came with 2 top ends, one for 9x19 and one for 9x21 with a simple 3 port comp. My question is: If we decide to shoot major loads with this gun is there a good reason to choose one caliber over the other? I know the 9x19 brass is cheaper/easier to get. But what about load "friendlyness" especially for a young shooter. I have a box of 147gr bullet

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