Where do get cheapest, safe, lead shot bags for Caldwell Leadsled?

[CraigC]

I've been using a sled for over 10yrs without issue. I've never busted a scope, a stock or had a scope slide in the rings. I never used what I would consider too much weight either. No more than 50lbs, usually just 25lbs. Recently upgraded from the original to the latest and greatest but have yet to try it out.