I've tried to follow the basic rules to ensure no major catastrophic mishap but I am guilty of a mistake or two. I recall one occasion where I was reloading 7x57's working up a load for my deer rifle. I had two or three boxes of new brass most of which I'd prepped in advance. I was working on ladder tests and I decided to try one more load so I grabbed a half dozen pieces of brass from another box. Everything was going well until I decided to shoot the last test. I chambered a round squeezed the trigger and herd nothing but the click of the trigger. I unchambered the round, chambered another and the same thing happened. When I opened the bolt I noticed kernels of powder in the chamber. Upon inspecting the rounds I realized that I neglected to prime the last half dozen cartridges I'd loaded.