Rusty: I have owned and used two different cappers in my day: One a straight line, sold by Navy Arms, and the newer one being an oval shaped capper from Tedd Cash products. Both are designed to allow a percussion cap to either fall forward into the opening, or be pushed forward against flat springs to make them available to be placed on the nipple. Once you push the caps down on the nipple with the capper, you simply slide the capper sideways, at 90 degrees to the nipple to remove the capper. Done.
I do not, as a range officer, nor do I personally, put a cap on a nipple with my thumb, or any bare finger. THAT IS DANGEROUS If that cap goes off, your thumb or finger is not going to be very usable for quite a while. I don't see the safety concern. I certainly would never recommend using Musket caps instead of percussion caps for any reason relating to safety. I believe the instructions that come with cappers adequately explain how to use them. Of course, you always will have total morons getting ahold of all kinds of dangerous implements, like matches, and someone does need to watch over them and teach them how to use these things safely. For most of us, this was our parents! And we were about 5 years old, tops when we learned those lessons. I suppose I was a lot older- maybe 12( retarded, you know)- when I got around to learning about handling percussion caps. I attended a civil war demonstration where the shooters were using musket caps, and putting them on the nipples with their bare hands. My father made a point of telling us how dangerous this practice was, and told us to never do it. I didn't need convincing.
If you are shooting a Civil War era rifle or musket that is intended to be used with musket caps, then use them. If you are going to use one of the subs now available as powder, where you need a much higher flash temperature, you have a choice in using either Magnum percussion caps, or musket caps. Either will ignite the subs okay.
Other than those exceptions, there is no need to use anything other than a standard percussion cap. If a #11 is too loose on your nipple, but a #10 is too tight, get a different nipple, or pinch the #11 caps a bit to make them grab the nipple. I always carry a pair of needle nose pliers with me when I am shooting percussion guns. I generally don't need them for my own gun, but have them available to help others. If you know how to use a knife blade correctly, you can pop a stuck cap off the nipple with one short stroke. My percussion guns have a triangular shaped cut in the hammerskirt, in the front, so that on firing, gases that blow back raise the cap off the nipple, and blow the skirt of the cap out and forward, away from my face. This breaks any seal that might otherwise happen, and the caps tend to fall off the nipple as soon as I lift the hammer to half cock, and give the gun a slight jerk or flip to the side.
Using musket caps to increase some kind of safety margin is going at the issue backwards, IMHO.
