Possible primer?

Was recently metal detecting and found what apprears to look like a primer or black powder primer, it’s 3mm tall, and 9mm wide. It has some parents which appear completely symmetrical and looks like it would fragment easily I also found a numerous what look like shotgun pellets or musket balls in the general vicinity which may correlate?

Any information or ideas is appreciated, cheers Hamish.

That appears to be a part of a 2 piece clothing button. The back or shank half is missing. Ca. 1840ish to 1900