All right! I want to be like BullSlinger, to never have to fully take apart a revolver. Time will tell.
I just fired a cap with keeper on! It was quite harder to put a cap on a nipple with keeper already on the cap. When fired, there was no sparks. (Or much much less sparks than from two caps I fired last week.) The cap stayed at its place the same as it was before firing it. Tight and retaining its form. The "keeper" was not damaged, but from a transparent one it became a dirty one, almost black. The top of the cap got opened like a can when I fired it. So I took a tweezers and grabed with them that opened top part, and that way it was pretty easy to pull it out. They came off the nipple together, cap and "keeper". While holding that keeper between fingers, it was easy to push the spent cap out of it with a small screwdriver. The cap body stayed mainly the same as it was. I can use that keeper again and again. If vinyl ones will melt when I load a black powder, I'll use silicone ones which won't melt. I agree that the whole process with keepers takes longer and complicates things. I'll use them for now, will see for the future.
I've just realized - if cap stays put when hammer strikes it - then NO NEED FOR SAFETY GLASSES, right?