case fully into the die. These discus- sions prescribed a simple trial-and-error process: Adjust the die away from the shellholder about one-fourth turn, size a case and then try to chamber it. Un- less the chamber, die, or shellholder was terribly out of specification, a case resized in this manner would not freely chamber. In that situation, one was sup- posed to adjust the die about one-eighth turn deeper into the press and size the case again. By trial and error, one would eventually find a setting that would al- low the resized cases to freely chamber without the resizing process engender- ing excessive functional headspace. This seemed a perfectly logical approach; so, I tried it for loads for my Remington pump-action 270 Win- chester. With no other changes, that approach at least doubled the resulting group sizes! I compared three sets of loads side-by-side at the range. In all three instances, loads in the cases that supposedly fit the chamber better shot lousy groups and loads in the cases that certainly were too short to best fit the chamber shot groups that most bolt- action elitists simply would not believe. When I figured out why that
method did not work in that gun, I never again practiced that method for any loads used in any gun. The follow- ing discussion should clarify why I lost interest in that method. WHAT IS WRONG WITH THE
HISTORICALLY RECOMMENDED METHOD?
Nothing is 100% rigid. To prove the point, even the surface of a neutron star vibrates (within the knowable universe, a neutron star is – by many orders of magnitude – the most rigid object possible). If the surface of one of these immensely dense and immensely solid objects vibrates then it must also be flexible. Those being facts, no press or loading die is perfectly rigid. And, no two cases are identical in every aspect. Within any given batch, the cases will vary more-or-less in wall thickness, uniformity of wall thickness, wall hardness, and uniformity of wall hardness.
Moreover, no handloader can ap- ply a precisely uniform and consistent coating of lubricant to every case. And, no handloader can resize all cases at ex- actly the same rate during each portion of the resizing process.
Explanation of case stretching and separation:
Left: Chambered round just after striker impact and primer ignition have driven the case forward until the shoulder begins to support it in the chamber. The force generated by the primer explosion within the partially enclosed primer pocket is several hundred pounds, which pushes the case forward. Note that the primer protrudes from the case head and that a significant gap exists between case head and bolt face. This reflects the functional headspace of the round – the greater the functional headspace, the greater this gap would be. Middle: Chamber pressure has risen to about 5,000 psi. This is sufficient to expand the entire hollow portion of the case body until the chamber wall entirely supports the case wall. As chamber pressure continues to increase, friction between case and chamber soon reaches a level where the case wall cannot slide.
Right: When chamber pressure generates more thrust on the case head than the case wall can support, the head moves rearward until the bolt face provides support. Because the case wall cannot move, if the case head moves beyond the elastic limit of the stretching portion of the case wall, permanent case wall thinning will occur. This thinning occurs within the transition zone between the solid case head and the hollow case body. Usually, modern cartridges generate more pressure than the case wall can support and usually, if functional headspace significantly exceeds about 2/1000-inch, elastic (permanent) case-wall stretching will occur within that zone.
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For these and other reasons, when-
ever the shellholder does not solidly abut the resizing die at the end of the case resizing process, the gap between the end of the die and the top of the shellholder will be different for each case resized. It will be lesser for softer cases that are uniformly and sufficiently lubricated; it will be greater for harder cases that are poorly lubricated; and, it also will differ even when all else is identical in response to how fast the handloader resizes the case or for other reasons, such as temperature variation as the die and press heat during the process of resizing a batch of cases. Because the length of the resized
case body is a function of the distance between the die shoulder and the top of the fully-raised shellholder (face of case head), variations in gap between top of shellholder and bottom of die represent variations in case body length, which will represent variations in functional headspace when those cases are cham- bered in any given gun.
As an example, in a preliminary experiment, I removed the decapping and neck expanding assembly from my 270 Winchester full length resizing die
and installed it in my Redding Ultra- Mag press so that the die just touched the shellholder of the fully raised ram. (Of available presses, the Ultra-Mag is among the most rigid; and, among modern cartridge cases with which most handloaders work, the 270 Winchester is about midway in size and degree of toughness with regard to resizing.) I then cleaned and carefully lubricated a once-fired 270 Winchester case. I then
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