To be honest, I'd have no problem trying max my gun's potential to what the rules allow. If they insist on chronoing with .2s then go with it. Hit 495 on that (a little leeway to be safe) and then swap to .43s. You won't have done anything wrong by their rules and you'll benefit from it, strictly speaking it may not be in the 'spirit of the rules' but then if they ignore joule creep then that's up to them. I'd just go for it, especially if you're doing a sniper rifle build.