In my opinion, double charging is less likely to happen on a progressive than one a single stage. I have used a Dillion 550 B for more than two decades. Sure there have been times when I weighed some loaded cartridges to make sure they had powder, or were not double charged, but I have loaded well over 70,000 rounds on the thing. Probably closer to 100,000 rounds. And no double charges or empty charges to date. Keeping my fingers crossed by Gum!..
The chance for a double charge occurs when you get interrupted. Maybe the bullet was misaligned in the seating die and you had to stop and remove a crushed case. Ditto for the sizing die. Maybe the primer did not feed. Something like that. When interruptions happen, and that includes phones and friends, you have got to teach yourself to double check everything before you pull the handle again. Regardless of what you remember doing when you were interrupted. Allow doubt in your ability to remember, acknowledge that you have early advanced Alzheimer's, and follow a process, not your memory. Typically, I pull the pin on the case under the powder die, remove that and dump the powder in the measure, finish with the case in the seating die, clear the press, and start with the empty sized, belled and primed case on station two, and a new case on station one.
Again it is my opinion, but double charging is most likely to happen when using a single stage. Instead of a continuous process, such as the progressive gives you, you have this batch process. And it is in the charging of the cases where you have the greatest chance of error. I used to examine each and every case in the loading block with a Maglite flashlight, and on occasion I would find an empty. It is easy to get out of sequence when using scoops, or even the little Dandy powder measure. Maybe it was because I had too much time to daydream; whatever. Because my mind is so often in la la land, I think it is good practice to use bulky powders when using a single stage press.
Before I got my progressive I used to be scared of fast powders like Bullseye. It is well known that a double charge of Bullseye will blow the pistol. Not any more. I have my process and practices down. I have successfully loaded so many cases of 38 Specials with bullseye powder that the fear has gone away. Bullseye is now my favorite powder in 32 S&W long, 9mm, 38 Spl, 45 ACP. I just have to pay attention to my process, and double check when I am interrupted.
