SUPER cool Taylor3535! After intense research the casing looks to be a caliber of a Rimfire ammunition although the picture does not allow me to make out size. Good luck with search.
I’ve found rocks like that too. Wondered if they were caused by a softer rock which has dissolved, or if it were a tool of some sort. I always keep them, the wife hates it.
Welcome from NW CT, Taylor. The shell casing appears to be a 22 caliber. I;ve often found them to be reddish color depending on how they react to the chemicals in the soil.
HH
dts
Limestone has a tendency to have what look like drilled holes in them naturally. That is what your rock looks like. Welcome to the party...Hope to see many more finds. Good luck and Happy Hunting