Single stage ancient Pacific press w/stand-alone single stage powder dropper. (Because.......I've always intuited that the S-S device is "more controllable" and less likely to mischarge, overcharge, double-charge, whatever. Maybe; maybe not. I do check powder charge weights about every 10 rounds or so and continually watch the vernier scale to ensure that it hasn't moved. Trying to be meticulous, which is why this KA-BOOM! has me somewhat confounded.)
No system is perfect. Personally I am completely sold on the auto indexing progressive. I have only had 4 rounds with issues (all squibs) and that was on a 550 which was having issues and causing distractions. ASSUMING all the automatic operations of the press are working correctly, you are much safer iMHO when the operator has less to do. All I have to do is...
1) Verify that the case has powder and that it looks correct (mine fills the case about half way)
2) Set a bullet on the case
3) Pull the handle down
4) Push the handle up
5) Go to step one and repeat
I have all the buzzers that tell me if the powder or primers are low. I have never understood the "You should start on a single stage to be safer" attitude. On my progressive, I can run each station and see what it does, just as if I was running a single stage. It doesn't hurt that the Dillon is a fantastic machine that does it's job correctly and accurately over, and over, and over again.
What is the most significant error that can cause a dangerous reload? Powder charge? That's not a rhetorical question. I am too new to think of all the possibilities, but I would guess that is the most likely. No primer? I will see that when I put the round (bullet down) in the ammo box, or it just won't fire. Worst part is the powder that dribbles everywhere. If a primer doesn't get seated all the way? Again, I should see this when I put the rounds in the ammo box. I caught it before. Worst case scenario, it will fire when it goes into battery. Hopefully my practicing the motor skills of safe gun handling will pay off and the gun will be pointed in a safe direction. Bullet not seated correctly and/or it is not crimped enough? It probably won't feed. Bullet seated too deep or not far enough? I measure the first couple of rounds from each reloading session and then measure intermittently. Any single round that is WAY off will be obvious in the ammo box. Again, I've caught it before, but that was on the 550. I'm sure there are many more possible issues, but these are the most common, with too low/high of a powder charge being the most egregious. So far I've loaded between 6 and 7K with my XL650, and I haven't had any major problems <Insert Fingers Crossed Emoticon Here>.
My personal opinion, but one that is reinforced by historical observation of the chain of errors leading to an accident, is that the less steps a person is given to complete, the less likely an error will occur. There are caveats, but that is a pretty solid rule.
Fly