I used to use a short dowel to check loads after charging the cases. I didn't have a progressive loader.
Drop the dowel down each case and make sure it falls in the same amount.
Caught a couple of squibs, and one overload when I first started doing this, cleaned up my loading procedure by making sure I was not interrupted by anything while charging, including potty and 'fridge breaks, and going from case 1 to case 20 (or 50) without stopping.
This was pursuant to a recommendation in one of the gun mags. I forgot who offered the suggestion, but it was a big-name gun writer.
Hatcher has some extensive comments in his chapter on barrel obstructions.
He discovered he could blow a bullet out by pulling a bullet and dumping about half the powder out, chambering the case + powder, and firing. At first, he thought this would be a method worthy of recommendation for clearing squib loaded bullets in the field, and experimented quite a bit with the method, trying it with bullets and other things like cleaning patches stuck in various places in the barrel .
One thing amusing to me was his description of setting off one of these "clearing" rounds and having nothing happen. The lab staff wondered if all that gas was just stopped up in the barrel, and used a broomhandle to tap the bolt handle upward until the bolt snapped open with a loud POP and smartly ejected the case.
Whew!
Bear in mind he had plenty of rifles to experiment with, being associated with Springfield Armory at the time.
After a while, he decided there were too many variables involved to make it a general standard method, and ended up recommending against using it at all.
He should know.
Right?
(ref: Hatcher's Notebook, "Experiments with barrel obstructions," Chapter VII, pp 180-197)