Maybe a four winged musket cap crimped a bit to stay on?

https://www.grafs.com/catalog/category/categoryId/3511

Mike

p.s. sounds like you have a gun using #12 or #13 caps

https://www.muzzleloadingforum.com/threads/13-percussion-caps.79027/

Last edited by skeettx; 07/16/19 06:43 AM.

USAF RET 1971-95 [Linked Image from jpgbox.com]