The factory spring weight is 17lbs. You can go down to 11lbs and up to 22lbs. Check out this link for ordering http://bit.ly/iYhdYq
Watch the ejection pattern of your brass. If it is flying out there 10 feet or so, you need more spring. If it is rolling off your knuckles you need less. Ideally you want the brass landing about 2 feet away.