Pancho, I wondered about the caps allowing a spark by. I can recall the brand I used the day I had that chain fire.
SS, it is important to know there are at least 2 types of caps uyou can use. CCI makes a crimped style, which usually seem a bit snugg, and may be the better to use. Sometimes these will be struck and nothing happens. If they are struck a 2nd time they go Boom.. What has usually occured is the cap wasn't seated fully on the nipple.
I find when, once as many caps are installed as I plan to use, usually 5, I go around very carefully and thumb drop the hammer on each one real slow, and press down on the hammer with the trigger still pulled.
Batches of tins vary enough, that I don't always need to do that task, but once a tin of caps shows this particular tins caps are too snugg, then I do.
Remington makes a 4 skirted cap, and these can tend to be looser, and may fall off in holster carry, and sometimes fall off after just being installed, upon recoil.
If you are in the act of shooting and notice a cap on a charged chamber is missing, stop shooting and recap the missing chamber.
I am a bit to primitive to have even heard of lube pills.
Probably I am wrong, but I wonder if these are no more than a oiled over the ball wool felt?