I think David was directing his comment to me (the OP) and the basic use of handloads in a fully automatic weapon. And that point is well taken. I have managed to stick two in a barrel over 20 years ago. One on my wife's .380 auto and one in my old .41 magnum revolver. Both were primer/lubricant related. No damage but neither were full auto either. And I have made corrections in my loading procedure to keep that from happening again. I may well have 250 rounds that I will use in my 1911 instead of his Mac-10. Or his in a trade for some of the factory ammo he is buying for this weekend. He loads as well but has just recently started and isn't loading for the Mac-10 yet.
One thing I did think about as I was loading the first half of the 250 I plan on using this weekend. The load called for Federal 150 primers. As I recall, the Federal primers are one of the softest primers on the market. Is that a concern with a fixed firing pin?