I've snapped a few prop bolts myself. The last one was just after coming out of an elevator I was going to do a warm burner pass down the runway. The engine sounded funny, so I landed. I had sheared three bolts.

There are a couple reasons that the bolts will shear. One is if they are over tightened when the prop is installed. There is a torque spec for the bolts, but I forget what it is. I'll try to look it up and post it. Another is if the hole for the prop bolts are not drilled perfectly straight, you can add quite a bit of shear tension which would shear the bolt under stress.

I've found my usual reason for shearing a prop bolt is misaligned prop bolts. You can usually tell when you are installing the prop, and a few of the bolts are tight going in. Even with the accessory DA or 3W drilling jig, you need to pay attention to get the holes drilled straight and true.

A choke servo is great as roger stated. Makes starting very easy. I have my choke servo on the snap roll button on the 10X. I hold it while I flip the prop. When the prop pops, I let go of the choke button, and it just keeps running. Saves me from the flip, pop, flip again approach. And it provides an alternative shutdown for the fiber optic kill should it fail.