The XD9 is more than enough gun for IDPA. Get a good kydex holster like a Comp-Tac or a Blade Tech, a couple of mag pouches, and go shoot. You will be shooting in Enhanced Service Pistol division, which isn't a really big deal, because initially you're not going to be competing to win matches anyway. Just go shoot your XD, shoot a couple thousand rounds through it, and then decide if you want to upgrade to a different gun. But don't just buy a gun "for IDPA" - consider if you want to shoot other games and such with it.
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