You might be the modertor, but you don't know much about the MAS failure that DHG is refering to. Had he not been wearing eye protection, it is most likely that the blade that gave away would have been embedded in his brain through the eye socket. As it was, he nearly lost use of the eye.

Cutting down props is often done to achieve a higher rpm for break-in. I recommend using a 10-6 WOOD prop cut to about 6" diameter for this application, so you have plenty of meat at the hub to hold it together. This is for when you need that 40 sized engine to turn in the 25k to 30k range.

Treating any high performance engine/prop combination like your sport engines is a great way to suffer injury or death.