Marker seems plausible. The casing, which is what it was written on, isn’t fired through the barrel. It’s ejected after, usually out the side. As far as size, writing ‘depose’ on say a 9mm cartridge seems pretty small, but not impossible, you could do it. Challenging, but not impossible. The casing is about .75" long and .4-ish inches diameter, and usually steel or brass, to give you an idea.
Marker seems plausible. The casing, which is what it was written on, isn’t fired through the barrel. It’s ejected after, usually out the side. As far as size, writing ‘depose’ on say a 9mm cartridge seems pretty small, but not impossible, you could do it. Challenging, but not impossible. The casing is about .75" long and .4-ish inches diameter, and usually steel or brass, to give you an idea.
Maybe you could write it on a diagonal or something. Like spiraling around the outside. Instead of in a straight line like I was thinking.