Rifle actions can sometimes behave in a different manner when operated easily and sedately, than they do operated hard and fast.....and sometimes differently if operated from the shoulder than at waist level(this more due to how we operate it from that position than anything else).
Did I read it right that you did your test with only two rounds but not a full magazine?
Still, it seems to me that 6 failures out of 20 attempts is pretty high.
I did much the same thing in live round rapid fire with a Rem 700 KS MR 7 Rem Mag and full magazine and it worked fine.
