I've found that the varation in the lenght of 9mm cases directly affects the amount of crimp on the case. The shorter cases are below the minimum lenght in my case gauge. The reloaded round sits too deep in the gauge and I can get light primer strikes in my Glock. I use a stainless steel match grade barrel in my Glock so I can shoot lead bullets. The SS barrel fully supports the case. Federal primers solve the issue 99% of the time. The light primer strikes cases will fire 95% of the time in my M&P 9mm & other 9mm's. I've changed the striker, spring, etc in my glock to no avail. Also tried using other Glocks & still have an occassional light primer strike. Primer seating is correct. I'm convinced the cases shorter than minimum case lenght are the issue. To verify I will sort 250 brass cases shorter than .754 to see if there is a difference in light primer strikes between the .754" longer & shorter cases to compare.
