This is happening because the ogive of the bullets you are using is not consistent. There is nothing wrong with the dies. I have this happen with bulk .223 FMJ bullets when I load up plinking ammo for my AR's all the time. I'm not getting .010 difference, but usually around .003 to .005 is somewhat normal. Winchester FMJ's are the worst. This last batch of Lake City 55 grain FMJ's have been the best, with as little as .002 variance.
I wouldn't worry about it. One thing I always do is clean the tip of the bullet seater plug with a paper clip, and a Q-Tip saturated with alcohol. Stuff can get packed up in it like paper lint from the boxes, etc. OAL differences of just .010 isn't going to effect anything unless you're seating at or near the lands. Even then take an average and seat .010 to .015 below that. You won't get much group dispersion or velocity change with that little variance. The only way around this is to seat deliberately long, then bring in each round individually to correct OAL. That would be a royal PITA.