"Bloody 7th Custer's old regt" 30-40 Krag

I got this in a 50 cent bin in Linden. The headstamp is “F 3 98”, very faint year stamp. Why would someone write this? I rotated the round 3 times for you to see the writing.

Perhaps markings on a souvenir round taken home by someone who served in the 7th Cavalry circa 1898-1907? Something to show the kids and neighbors to brag about his service?