Never had 'em drop down on me like that. If you feel that it's not a bedding issue, then it's the load or part of the combination I would think. I guess I would check with a known good shooting load to eliminate gun/scope problems. How did you weigh the charges? Check the scale? Do anything different than normal? I know this sounds elementary. No switch in primers while loading?
Hope someone else on here can help. Let us know what you find out.