Since some posters seem to think that a healthy respect for primers is akin to paranoia, let me relate some experience that I acquired while much younger, in a society that tolerated such foolishness:
I happened to have some Remington .44-40 smokeless powder loads that I had decided I did NOT want to shoot in a very old 1873 Winchester (made in 1884, I think). So, to me, those cartridges were useless and surplus. This was in the days when cherry bombs were legal and plentiful, so loud explosions did not bring the police unless you actually blew-up something that belonged to somebody else. So, a few of us decided to see what would happen if we taped a thumb tack to the bottom of a cartridge with the point against the primer and dropped it off a bridge onto a concrete pad. With a little tape "tail" on the bullet's nose to make the cartridge fall stably with the primer down, we found out that those rounds went off with a bang that made cherry bombs come in a close second. Of course, we were careful to avoid exposure to the brass shrapnel. Pieces of the case and the bullets were hard to find on a pad that was the width of 2 road lanes. (They were the old balloon head cases, so there was not much mass in the case heads for these particular cartridges, and we never found even an intact case head.)
So, the moral of this story is that IF a primer goes off in a loaded cartridge that is not confined in any way, it very well may EXPLODE rather than simply poof the bullet out of the case.
And, sometimes a primer DOES go off while being seated. It only happens rarely. But, it happens while seating a primer in a loaded cartridge, see "bang" above.
So, while people can and do get away unscathed while doing dangerous things, that does NOT indicate that those things were safe to do.
Ok, now the information is out there, and each of you can make an INFORMED choice about how YOU will handle YOUR OWN little problems as they come up.