I've got to agree with Darryl on wearing glasses. This was strongly re-enforced to me 2 weekends ago.
I was firing in my first ever F-Class match at Butner, NC in a 600yd 3 match Agg match and my 11th shot in the first match had a primer rupture (not a peircing from pressure but from a primer defect) on the edge of the primer. When the shot fired I saw the black smoke from the action and felt my face get peppered with particles. If you look at my eyeglasses now it looks like they got hit with a violent sandstorm on the left lens (I'm left handed). If I hadn't been wearing them...........
And this wasn't even testing loads. This is a known good load of H4831 and the same lot of primers that I've fired probably 300 primers out of already in 65F weather. I've fired this same loads for 2yrs in much hotter weather then 65F.
That one primer was defective somehow and cracked down the edge of it and allowed the gas to leak out a pin hole on the edge. It blow the ejector back into the bolt (which I haven't been able to get back out yet) and burnt the bolt face as Ian eluded to above with some gas cutting around the extractor also.
The only good thing was the shot was still an X to keep my perfect string going. Ended up with a 600-38X and finished 4th that day. I fired another 40+ rds after that primer rupture without incident using the same componets.
Look at the one on the left. see the little hole under the arrow? Maybe it was supposed to come with such a hole, but that one didn't. If the primer blew out or pierced, all of the gas vented at the back of the bolt.
The holes on the M70 bolt ( right ) measure .1515
If I can kill that coyote from here, Will you walk out to get him?