WADR, the only accidental injuries I have seen first hand, or heard of, to thumbs, occurred when men were pushing tight fitting Musket caps down on dirty nipples. The caps went off, causing both blisters, deep bruising, and in one case a major tear that required a couple of stitches to close. I am sure that similar accidents have also occurred when thumbs were used to press down a #11 cap on a standard nipple, too.
It makes no Safe sense to put caps on a nipple with your bare fingers- no matter what caps are used. USE A CAPPING TOOL.
I began shooting percussion caps using a straight line capping tool, sold by Navy Arms, back then. But every supplier sells this simply tool. I "graduated" to using a Tedd Cash products oval capper, because I could dump all 100 caps from a tin into the capper, shake it a few times to turn all the caps right side up, close the lid and forget about it for months of shooting.
More important, using the capper put metal behind the cap- not my flesh.
Drilling out nipples is a dangerous practice and an invitation to an unnecessary accident. :nono: :shake: Go visit the slug gun shooters and bench rest shooters at Friendship or other major shoots around the country. They represent the "Research and Development" side of this sport. They will tell you lots of horror stories about fellows who screwed around with their nipples, and saw their guns come apart.
My brother had a nipple disappear one day when he was firing a mild load of 40 grains FFFg in his .40 caliber percussion rifle. It seems that the factory nipple was an American thread size, but the bolster was metric. He was lucky in that he wasn't injured, nor was our father, or me, standing behind him as he fired the gun. The nipple sailed up and over all of us, and was lost in the coarse stone in the drive to the range behind us.