The last IDPA match I shot, I was allowed to shoot from aiwb. I think that's awesome. But I think it's very important that people who are shooting outside the rules be identified as such on the scoresheet. IDPA used to allow "outlaw" gear at local matches and the result was painful: people showing up to major events, even Nationals, with illegal gear and either believing an exception would be made or in some cases not even realizing the gear was illegal.
Not for nothing, but if you recognize that a good grip helps you win, the guy who modifies his pistol to achieve a better grip does have an advantage. More importantly, it can be perceived as an advantage. The whole idea behind "stock" classes is supposed to be that the new shooter can step in and play with the gear he's already got instead of going out to buy something new or spending money on expensive modifications.Is the grip reduction going to result in this guy beating the shooter just above him?....I seriously doubt it. You just don't get that much of an advantage. What makes a difference is training, trigger control, proper grip....fundamentals.
Seeing as how the dude with the grip reduction could just shoot ESP there's no reason to let him shoot SSP. Unsanctioned match or not. Also drops everyone below him an unnecessary place in the final log. And they also may be the sort to never shoot at anything but a club level.
Welcome to Africa, bring a hardhat.
Although you've had some good input on the thread here, for a definitive answer, simply go to the official IDPA site and pose the question there-I believe there's a specific spot for resolution of just this sort of query on the site forum...
Best, Jon