Ant, best to fire the bottom barrel first. As it's in a more direct line with your shoulder, you will get less muzzle flip. If you need to get onto target you'll have an increased chance of doing so. A small difference, but can make all the differencei don't usually need a second shot ;-p lol no seriously I think the only reason I shoot top barrel first is because it's easier to take out the top cartridge if you've only fired one or swap cartridges if you spot Charlie etc