Squibs are more a function of individual process than equipment. The key thing is that you have to have some step in your process that verifies there is powder in the case, either automated (powder check) or visual, preferably both though that isn't always possible. It's very very difficult to have a squib with an autoindexing progressive, but it can happen. Same with a single stage, but it can happen. Probably the easiest platform to squib or doublecharge is a manual indexing progressive. All 3 systems require a verification check. If you single stage load, then you have lots of opportunities to do a visual check....you can check when you fill a case, again when all your filled cases are in a load block......easy to spot a double charge or an empty when you can look down into all your filled cases at once. You get to check a third time when you pick up the case to seat the bullet. On a manually indexing progressive, you've got to visually inspect the case for powder as you index it. Look before placing the bullet....the manual index step is your fail point here...index it twice, you get a squib, forget to index it, you get a double. You still need to make a check on an auto indexing press, but it can be harder to see inside a case. Some guys rig up cameras or mirrors if they can't get a eyeball in there, or run a powder check. The fail point on a auto indexing press is some sort of failure on the plate that causes a stoppage. The extra anal OCD of us will completely clear the shell plate for a stoppage, thus making sure that you don't skip the powder station, or inadvertently send a case through twice. Distractions, being in a hurry, or not maintaining your equipment are all factors that can contribute to a squib or a doublecharge.