Once again I'm gonna play the cynic; I doubt that the OP's sprag failure was really that spontaneous, probably in distress before the R&P failure.
Every one I have ever seen was "spontaneous" or related to a specific indecent of extreme shock to the drive train
Of course, the
failure was spontaneous but if you hadn't physically inspected the sprag one run before the failure how do you know its condition before the failure?
I've pulled apart plenty of 727's that were working just fine but had rollers with visible flat spots
As far as checking the sprag on rebuild, if the pins are straight, move on. Not believing failure could occur on a new sprag when a driveline part brakes, when it free-wheels and slams back under load, no way is it strong enough to not damage or brake it. The sprag was never designed for that kind of abuse. As far as explosions, I'd say the driver is not paying attention to what the "car" is telling him. A simple test to do after your burnout, put in low, push throttle to reset the sprag rolling foward, if it feels not right, abort the run, you broke it. Never roll-coast to the line after the burnout. By the way, I've done first-second-drive burn outs forever and never broke a drum, but have broken two sprags hitting wet spots after the burn out box on dry hope and feeling the results.
