Started thinking about this and what people are doing to prevent it. I see lots of gizmos and I admit I have one (Powder Check dies for the 1050 added about 10 years ago). Mirrors, LED lights, visual inspection....
At 70 I have been doing this for a long time and have been "lucky" so far. Started to wonder why, because I have the wrong mindset for reloading. For me, it is a means to and end...getting affordable ammunition in as little time and with the minimal effort possible. Never had a double charge....why??
100,000's of thousands of rounds. And I expect 99% loaded on those "tricky" progressive presses. Most of my pistol reloads have been .38 Spl...one of the easiest cases to double charge.
I have used two Stars, a Green Machine, three 1050's, 650, two 550's and two SDB's for metallic. MEC 650, MEC 9000, Dillon 900SL, Ponsness Warren 800C, PW 800+ with AutoDrive, and Spolar with Hydraulic for shotshells. Loaded a bit on a buddy's Camdex but it is an "ammo plant" so not counting it.
At least for me, the auto-indexing progressive press is the safest way for me to reload. I have one 1050 and one 550 for pistol reloading. The 550 is nice for smaller runs and cheap caliber conversions but I prefer running the 1050
It would be interesting for those who have had a double charge to weigh in on how you think it happened. I suspect most double charges occur using a single stage or turret press.