So I went up to shoot my AR. I had shot a couple of mags and noticed a jam. cleared it and continued to empty that mag. I started picking up my brass and notice a case with out a primer, then found several with indentations on the case base. The indentations matched the poped primer. found another poped case. I was shooting new brass cased federal 556 55grain ammo from bi-mart. Is this a normal thing that happens? I shot several more mags and only had it happen one more time. I did pull the bolt and check everything before doing more mags. no signs of over presure, deformed bulging cases. Could this be a bad batch of ammo. I have been using it and have over 2000 round down the tube with no problems. Thanks in advance for the help.