Re: New RCBS Dies ... now shaving bullets ... ?
Your expander ball is too small. It should be .204", or not less than .203". Call RCBS for a new one.
And your case mouths should be champhered to ease bullet entry without shaving the heels.
What's real bullet "tension"? Actually, what many of us call tension is only the undersized, or what engineers call an "interference fit" between two diameters. In our case (litterally) the neck and bullet diameters are an interferrence fit and that's only casually related to real bullet tension. But, using the common term, the neck fit should only be 1 or 2 thousants undersized, no more, so a proper expander ball should be bullet diameter or 1 thou less, no smaller. With typical spring back that will give an interference fit of 1 or 2 thou, which is plenty to hold the bullet securely without excessivily working the brass.
When the necks are expanded - stretched - more than about 2-3 thou (it varies a little with caliber), it exceeds the elasticity limits of brass. The stretched brass will only spring back about 2 thou. no matter how far we expand it. Thus, when seating a bullet in a neck that is more than 3 thou smaller than the bullet, the bullet simply acts as an expander. So, even tho your bullets are stretching the necks more now, there is no more real tension than there would be with a properly sized expander ball.
You need to decrease the interference fit of your bullets, they are fixed so you must work on the necks. As you are finding, excessivily small necks greatly increase the probability of damage to the bullet's heel as it enters the much too small neck. AND, the excessive seating force tends to push bullets off axis and increases bullet run-out. Neither situation is good for accuracy.
Any cartridge brass will have, or certainly needs to have, "spring back". (For one thing, that's what allows us to extract the case easily after firing!) How much springback we get varies somewhat by the alloy but some is always there. Hard brass does have more spring back than soft but hard is also more brittle and prone to split. We anneal to keep the neck spring back in the proper range for best bulllet fit/tension AND to reduce premature splittling.
Improper annealing by overheating the necks to a red heat, a very common occurance with most inexperienced reloaders, will reduce neck springback to virtually zero. Excessive neck softness destroys any real bullet tension, no matter the amount of diameter/interference fit of the necks.
Last edited by boomtube; 03-29-2009 at 06:03 PM..