Ya M. De L., but I'm not going to tease Murphy's Law by squeezing a percussion cap in a vice. Ya, I'm aware a good forceful strike is required probably 99.9% of the time to cause a percussion cap to ignite, but again, by having to force a tight fitting cap to seat with a dowel, deer antler, or whatever, that 0.1% maybe probability is enough to say "Nah"!
Squeezing a percussion cap in a vice reminds me of a foolish kid some 10 years old or less that took a 22 LR from his Dad's 22 ammo supply, took it out to a weld shop, closed the door, placed the .22 rimfire on a vice, and wacked it with a ball peen hammer to see if it would go off. Yours truly here!!!
What a bang, my ears were ringing for quite a while! Never did find where that bullet went, never told my Dad about it until I was probably around 30 when I figured the statute of limitations was probably expired. Dumb kid stuff. Can recall the incident and doing every step like pushing rewind on a tape. Still here to report on it though.