The grunge you are talking about is actually the corrisve primer eating thru the bullet is garbage once this happens. But I have had some(very few) that I had to hit twice with no grunge. Maybe one or two in 1,000rds. which isn't bad but they did go off on the second hit. Now the question is what do you do when it doesn't go off the first time. Stay holding the gun for a few minutes then I reset the bolt(firing pin) and set it off again. I have heard about primers not being set far enough in on some of this military stuff too. There is a disadvantage and an advantage to using old military stuff and one must be careful. At my local range there is 55 gallon steel drums most likely thats what they are there for if a round goes off after its out of the gun the case goes and the bullet stays just like in a fire and in a 55 gallon steel drum its most likely to stay in the drum not much energy. I never used it yet but its there if needed. Remember safety first and have a plan for sure when things go wrong.
Be safe!!!!!!!! BigBill
Be safe!!!!!!!! BigBill