There are slight ID size differences between various brands of caps, too. This may have more to do with the amount of priming material dabbed inside than the thickness or dia. of the cap, though. If you've been using Remington, then try some CCI. My '51 Navy prefers RWS for the best fit. I have an 1851 Navy Uberti coming soon , thanks to Standing Wolf here at THR, also NOS, unfired, guessing 5-8 yrs old. I don't know what cap size this would take, 10 or 11. Also in my near future are probably a Pietta 1862 pocket, and it's smaller cousin the Uberti 1862 pocket police.
Quora is a place to gain and share knowledge. It's a platform to ask questions and connect with people who contribute unique insights and quality answers. This empowers people to learn from each other and to better understand the world.