Date: Jun 02 2007
To prevent “oversizing” brass, die makers recommend the time-honored technique of trial-and-error testing for minimum resizing. In other words, you back the die off a full turn after screwing it down to touch the ram/shellholder at the top of its stroke. That position would push a case fully into the die for full length resizing. But your rifle’s chamber might be slightly bigger than this. Since the fired brass has already stretched to that size, why squeeze it back? It’ll only stretch more on the next firing.
Keeping cases close to chamber dimensions improves accuracy, too, helping to align bullet to bore. This is why some target shooters like to neck size only, using the camming action of the bolt to force the tight cartridge into battery. Hunters, however, need ammunition that chambers smoothly and easily, so minimal body sizing is a good idea. To achieve this minimum sizing with your dies and brass, set the resizer die a full turn too high as described above. Run a case into the die, then chamber it in the rifle, noting how hard the bolt closes. An oversized case will make for a tight fit and hard bolt closure. Screw the die down a bit more and try again, continuing the process until the case fits with just a hint of pressure. The die is now set for minimum resizing. Lock it in place, using a small plate of steel between shellholder and die base to square the base in the threads.
I generally set up all my dies this way, but recently found two that wouldn’t minimally size cases even with full die/shellholder contact. What is going on? One of three things. Either the die was reamed too large or the rifle’s chamber was reamed too small or the shellholder is too tall. The simplest solution, according to engineer Patrick Ryan at Redding, is to sand the bottom of the die slightly. Tape a sheet of 220 wet or dry sandpaper to a flat slab of glass or steel plate and run the base of the offending die over it in a figure eight pattern, measuring frequently with calipers to check your progress. Also test progress by resizing cases as above and running them through your rifle. Alternatively, you could sand down the top of the shellholder, but then it wouldn’t be the right height for your other dies – unless you reset them all. If more than one set of dies seems oversized, the shellholder might be the problem. Go ahead and sand it thinner.