Here's another example--with the Lee Load-Master
Like with the others, it's harder to do--but I did do it, I think. Since I am not familiar with other progressive presses (except for the 550B, which I've seen and operated in the store, but not loaded on), I'll simply comment on the Load-Master--which I own, and use.
The load-master primes in station 2, on the downstroke. Its indexer is a simple lever that can be readily removed--and, at some points in the stroke, allows for reversing the stroke.
Powder is dropped in station 3. The Lee Auto-disk measures are expander operated. Those of us who use the Lee measures know that if they are being spring actuated for return, the disk / bar comes back to pick up a second charge the moment the case mouth clears the PTED on the ram drop. Some years ago, Lee updated the powder measure operation to remove the spring operation on their two progressives--i.e., the Pro 1000 and the Load-Master. They now have a rod and spring assembly that will manually pull back the measure to pick up another charge only at the very bottom of the ram downstroke.
The change took care of what is arguably a "design flaw" on a progressive press--that is, powder-drop dependent only on case mouth insertion or reinsertion, with a possibility that no indexing as occurred. However, it can still happen, AFAICT, on the manual-return measure.
If all elements of the system are not fine tuned, the operator can get the powder measure return as he begins to seat the primer--and therein lies the problem. The Load-Master primer insertion and seating can be problematic--and you can feel the resistance of a tilted / flipped / sideways primer (usually too late to avoid damage, or a crushed primer), so the operator reverses the stroke. Then it is the drill to clear the primer at the anvil and repair / solve the primer feed, etc. If the measure pull-back has not been properly set up--i.e., with a too-short chain, so to speak--you can get a double charge. Further, if the measure does not have a properly-tightened hopper or has a worn disk / bar, the weight of the pullback chain alone can draw back the disk to pick up another charge.
At this point the case at the #3 (expander / powder drop) should be removed and cleared. If you don't--or if you "fiddle" with the primer and case there, without indexing--you'll get a double charge.
I think that I doubled-charged a case last year when I neglected to do that--it was a simple primer-feed problem (one was just not pushed on to the anvil, because of insufficient primers to do the gravity feed), and I reversed the stroke, filled the primer tray--and ran the case through without indexing.
At least, that is the only explanation I can come up with.
added on edit: Note that I did not check the case visually--which is the real solution to avoiding double charges on a progressive. My excuse--between the case type (long and narrow) and the press size, it is virtually impossible to do without pulling the case. I need to rig a dentist's-mirror-and-light gizmo, I guess.
Personally, I consider auto-indexing to be a requirement for a press to be "truly" a progressive, so I've never been enamored of the 550. However, I fully understand there are 1000s of 550 users who do just fine; it probably really just matters to learn your routines well, no matter the press brand.
Jim H.
in the last 10 years or so with mine. I don't recommend it. It can be, well, let's say.... exciting. 
Very bad.
