ram stroke, I measured the gap between the shellholder and the die body. The difference between this gap and zero represents the press flexing associated with resizing each case. See tables. TEST #1 LIMITATIONS
With this die setting, the die shoul-
Custom Competition shell holders for cases with 30-30-size rims (Redding uses #2 for this rim size): Note that each shellholder is marked to indicate how much thicker (inch) it is than the standard shellholder thickness (125/1000-inch) – 12, 14, 16, 18, and 20 thousandths. Such extra-tall shellholders are a custom- order item and the delay can be significant but having a shellholder that allows correct, consistent, ideal full-length case resizing to fit the combination of a specific resizing die and gun is worth the wait and the expense. In the long run, this will save time and money (cases will last longer, will require trimming less often, and will produce more accurate loads).
der was just beginning to move the case shoulder. It seems likely that with normal resizing where the die moves the case shoulder farther rearward, stress would increase somewhat and therefore case-to-case variation in strain would increase. And therefore, variation in shoulder placement would increase. I could not test this because I do not own a set of thin enough feeler gauges to measure gaps of less than 5/1000-inch. Similarly, I do not have feeler gauges in increments finer than 1/1000-inch so these readings reflect only the actual gap to the nearest-smaller thousandth-inch. These measurement limitations
make little difference to the point of this study. With case-to-case variation far exceeding 1/000-inch, the point is proven – this case resizing method cannot produce consistent functional headspace from one case to the next. Perhaps I might buy a precision feeler gauge set some day. This would allow me to do a similar test with a nar- rower gap (so the resizing die is moving the case shoulder significantly) and with greater measurement precision. Mean- while, this test proved the point to my satisfaction: Effective headspace varia- tions of 2/1000-inch among same-lot once-fired cases suggests a significant reduction in accuracy potential with this full-length sizing technique. This confirms what I proved in 1967. Yes, with smaller cases (as we
typically use for varminting) we would expect to see smaller headspace varia- tions. But, eliminating any unnecessary headspace variation seems worthwhile to me because doing so is almost cer- tain to improve accuracy and to reduce maximum stretching of any case within the batch.
TEST #2
Standard Competition shellholder set for cases with 30-06-size rims (Redding uses #1 for this rim size): Note that each shellholder is marked to indicate how much thicker (inch) it is than standard shell holder thickness (125/1000-inch) – 2, 4, 6, 8, and 10 thousandths.
Page 138 Winter 2013 For test #2, I removed the decap-
ping rod and neck-expanding assembly from a 30-06 full-length sizing die. I installed that die into my Redding Ultra-Mag press. I adjusted that die so that when I fully raised the ram, the shellholder just touched the die. I used a Lee locking ring system with the lock-
ing nut tightened sufficiently to assure that o-ring compression would hold the threads in the die body snugly up against the threads in the press. I prepared a new batch of cases, as I had for Test #1. Using the same care- fully uniform press operation, I drove each prepared case as far into the die as the ram would force it. With each case in place at top of ram stroke, I measured the gap between the shellholder and the die body. Difference between this gap and zero exactly reflects press and die flexing associated with resizing that individual case.
On the 270 cases, I also measured
case body length. I listed this as NOMI- NAL BODY LENGTH; this represents the variation in functional headspace from the average of these five cases. At a whopping 3/1000-inch, it is not surprising that this exceeds the 2/1000- inch stress-gap variation because this measurement reflects total variation in: Stress gap Elastic die body stretching Case body springiness In this instance, cases that gener- ated the greatest stress gap also had greater spring back, which makes sense and probably is typical because cases with the hardest bodies will generate the greatest resistance to resizing and also will have greater elasticity (more elastic spring). I suppose I could prove this, or not, by testing at least twenty cases to compare stress gap and body length with the full-length sizing die set to almost touch the shellholder. For my purpose here (proving that minimiz- ing headspace variation requires that the shellholder solidly abut the sizing die during case resizing), I do not care about that aspect. Perhaps I will do such a study someday hence. LIMITATIONS OF TEST #2 With the die adjustment tested here, the die shoulder was just begin- ning to move the case shoulder. With normal resizing (where the die moves the case shoulder progressively farther rearward), we could expect that resiz- ing stress would progressively increase. If so, case-to-case variation in strain might be greater. I could not test this because I did not have the necessary feeler gauges to measure smaller gaps. Similarly, these readings are accurate to only the next-smaller 1/1000-inch
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