Elastic butt cuff works ok, as do the slings that hold 4 extra rounds. I like the cuff for a fridge that I may have to 'grab and go' such as a camp gun. I prefer leather military slings, so I don't use the ammo sling, but my daughter does and she likes it.
I like the Federal plastic cartridge sleeves that they pack their ammo in. It holds the ammo tight so it doesn't fall out, and it prevents rattles. I suppose you can even thread it on your belt, although I never have. They fit on the pocket just fine, and can be trimmed down with a knife to alter capacity if 10 rounds are too many. Best of all they are essentially free.
