by Bob Blaine
Copied with permission from Sinclair's "Shots" issue 1999-A
We all strive to get the most out of our reloading processes and tools. Our goals are improved accuracy and extended brass life, and a properly adjusted full length sizing die can help with both of these. Most die instruction sheets tell us to screw the die into the press until it is just barely touching the shellholder with the press in the maximlun up position. This setting should be adequate for most factory rifles, but we can improve upon it.
Full length sizing adjusts the "headspace" of a fired case by moving the shoulder of the case down to match the dimension of the die. Headspace is the distance from the case head to a specific point on the shoulder of the case which is known as the "datum line". Tools which measure this distance permit us to set the sizing die to SAAMI dimensions or to another headspace dimension of our own choosing. The full length die also brings the body of the case back to SAAMI dimensions.
Wilson case gages are die bodies with stepped cuts milled in the top and bottom. Simply insert a fired case in the gage and note where the case head orients on the bottom of the gage - if it is between the milled cuts, the case is at SAAMI specifications for headspace. If the case won't go in the gage, the body needs to be sized down, and a case head protruding past the milled cut indicates too long a case or "not enough headspace". The top of the gage has similar cuts where the case mouth protrudes - these indicate whether or not the case needs to be trimmed to length according to SAAMI dimensions. To use the gage to set up your sizing die; just keep sizing the case, checking it in the gage, turning the die down a bit more and so on. In just a few minutes you will be sizing cases which fit the gage perfectly.
The Stoney Point headspace bushing set works on the same principle. The bushings measure cases from the case head to the datum line on the shoulder. These tools fit on your dial caliper and you take an actual size reading. If you measure a once fired case and set your die to size to that dimension, your brass will have minimal headspace. This method of sizing will give you maximum brass life since the shoulder moves forward very little each time you fire the case.
If you are shooting a semi auto rifle or lever action rifle you should probably size your cases to fit in the Wilson gage easily. These rifles do not have nearly as much camming force to achieve bolt lock up as a bolt action rifle does. The Stoney Point tools can be used for this type of sizing also. just set your sizer to give you a measured dimension .001' to .002" less than a once fired case.
Many benchrest shooters size their cases a tiny bit every time they shoot them. This makes the 'feel" of the bolt closing the same every time they load a round. They size to almost zero headspace and feel they can shoot faster if the bolt feels the same every time. This sizing set up can be accomplished easily for a custom gun or a wildcat cartridge by using the rifle itself as a gage. Start with a hand full of cases which have been fired a few times. Remove the spent primers and clean up the neck with 0000 steel wool. The firing pin and spring should be removed from the bolt (sometimes this is a little difficult - we make special tools to do it on Remingtons, Stolles, Halls and some others). Insert one of the cases in the chamber and close the bolt gently. Pay attention to the force needed to lock the bolt up all the way. Lube the case and size it in our die then wipe off all the lube. Try this case in the gun again. If the bolt handle drops closed you have sized too much - throw that case away and adjust your die up a little. With a little tinkering, moving the die up and down in the press, you will soon have cases which produce just a little "feel" as you close the bolt. This is perfect. The reason for removing the firing pin and spring is so you don't feel the cocking force of the mainspring - you just want to feel the headspace of the case in the chamber.
All of these methods of die adjustment work well, so pick the one that's easiest for you, or fits your shooting situation best. Remember that minimal headspace makes the brass last longer and may contribute to increased accuracy. It may not be the best idea to size your brass by the benchrest method if you are shooting 500 rounds a day at a prairie dogs out of a Ruger 243. Set the sizing to fit the shooting situation.