Originally Posted by DocB
Sir, would you mind elaborating a bit on this. How would I go about determining the amount of grip being applied and what size smaller mandrel would be needed for 300WM? By sanding down a collet mandrel, wouldn't that increase the ID on the mandrel somewhat?
The amount of grip is up to you. General consensus is bullet grip from .001" to .003" (less than diameter of bullet)
You can get an approximation of bullet grip by measuring outside neck diameter of a sized but unloaded case and a loaded case, subtract the 2. Not very accurate
There are other tools. I use a set of pin gauges
You can order mandrels from Lee in whatever diameter you want (minimum order applies, $15.00 or more IIRC)
Some prefer to chuck the mandrel in a drill and hold sandpaper on it. I had miserable results with that, hard to get consistent results from top to bottom and keep it perfectly round, YMMV