I have a Dillon 550 setup for my cowboy loads only, and haven't emptied it in years. I figure if I keep the lid on the hopper/meter, its the same as having it in a plastic powder bottle. When I start to reload for the season as I live it the northern half of the country, I make several drop checks to make sure powder is flowing properly and charge weight is consistant then away I go. I load everything else on my other press and that one gets the powder changed quite often, but I always leave the current powder canister I'm using next to that press, so I don't have to guess what I have in it. LM