7.62 x 51 60 loose rounds poor primers

I got 500 of these mil surplus rounds in a bundle. I've fired off approximately 440. The issues with these are approx, 20% non fire, and all have had about a half second hang fire. The primers seem to be poor. I've been using these rounds to break in my rifle. The last 200 or so rounds have just been shot off just to shoot off and now id rather just use factory loads.