I'm all about getting the most out of things like tools and equipment, and that makes me a utilitarian. Using tools for purposes that they were never designed for is what my vocational school electrical teacher affectionately called Primitive Pete.
Primitive Pete is your friend.
When you're prepping cases for reloading them, one of the steps is to clean all the soot out of the primer pockets. Sometimes the little tools and brushes that were designed for such a task do not remove that soot, and occasionally the flash holes will be blocked by a stray piece of brass that can't be removed. Also, if you're the kind of reloader that runs your deprimed brass through a tumbler, whether it's the first cleaning the cases get, or you want to re-clean them to get rid of the sizing lubricant, you've no doubt had the tumbler media get hung up in the flash hole in the primer pocket. That stuff can be a pain in the ass to get out.
Well, there is just the tool to remove all that soot, brass, and carbon:
That is a standard one inch paddle bit designed to drill holes in wood. You probably have one rusting in the bottom of that tool box that you never use, so drag that thing out and get your Primitive Pete on.
A word of caution: paddle bits are semi-hardened steel, so it can gouge brass very easily. Be gentle. If you look close, the pointy tip actually has a flat cutting edge that is great at scraping carbon from the bottom of the pocket, and you can also get the inside edge of the pocket to allow the primer to seat all the way down. It's the best tool I've found for picking out the tumbler media from the flash holes, and if you have a stray finger of brass blocking the hole than use the long cutting edges on the tip by spinning it to unblock it.
Now go forth and make some ammo!