Terry, APC claims redline is 190,000 divided by the diameter. I've had their props fail below this, so make sure to always work around this stuff with both eyes closed. [8D].
If you've got a 1/2A engine capable of throwing the blades, then you've got one that is both supercharged and on nitous.
So far I've never seen any engine below a .32 break APC's golden rule.