gap. As with Test #1, neither of these limitations makes much difference to the conclusions one can draw. As with Test #1, this test proved that unless the die is adjusted so that the shellholder solidly abuts the die during case resizing, variations in case-to-case resizing resistance will increase case- to-case variation in case body length. This will result in a significant increase in case-to-case variation in functional headspace of resized cases (see Test #3 table).
As we all know, consistency is
the benchmark of accuracy. Therefore, any case-to-case increase in functional headspace variation is almost certain to reduce accuracy potential. This con- firms what I saw with my 270 in 1975. Therefore, I am satisfied that if the shell- holder does not solidly abut the resizing die during the resizing operation, the handloader is giving up a measure of accuracy. Conversely, eliminating any unnecessary case-to-case headspace variation is worthwhile because doing so is almost certain to improve accuracy. For Test #3, I removed the decap-
ping and neck-expanding stem from my tightest 270 Winchester full-length
resizing die. I used that die to progres- sively resize each cleaned and lubricated case in steps. After taking an initial case headspace measurement using the RCBS Precision Mic, I adjusted this die until it was just snug against a fully raised case (my adjustment goal was to remove all slack in the system without applying any additional stress). Then, I turned the die one turn into the press and resized each case with that setting. Then, I used the RCBS Precision Mic to take body-length measurement for each case. Then I turned the die one-turn deeper into the press and repeated the size-and-measure process. I repeated this procedure until
the die was seven turns from the just- touching setting. At this setting, the die was sizing practically 100% of the case body before the die shoulder began to touch the case shoulder. With this die adjustment, when the ram was fully raised the shellholder-to-die gap was about 25/1000-inch. So, the die was not touching the case shoulder.
For the final measurement (listed as “ABUTTING” in the table), I adjusted the die one-half-turn deeper, to assure that the shellholder solidly abutted the
TEST #2
Random 30-06 Springfi eld Range Cases: Resizing Force Comparison Study
Case Make Stress Gap Comments (1/1000-Inch) 12 11 11 10 9
F-C
R-P 1 R-P 2 Win 1 Win 2 Win 3 Win 4 Win 5 Win 6
In a larger sample, such uniformity would be unlikely
10 9
12 11
Super-X 11 Mil-HXP71 9 Mil-TW 54 9 Mil-TW 54 11
Notes: The following factors would progressively increase the differential case-dependent gap between shellholder and die (and therefore functional headspace variation of chambered resized cases): • Less rigid press;
• Less uniform lubrication; • Less effective lubricant; • Sharper or wider case shoulder; • Larger or otherwise tougher cases; • Temperature variation during sizing; and, • Less uniform press operation.
Under these test circumstances, these measured case-to-case stress-gap variations are about as small as we could expect to see with 30-06 and similar cases.
www.varminthunter.org Page 139
Nickel plated same lot, fi red in same gun Newer nickel plated
Same-lot Frontier 270 Winchester Case-Comparison Study
Case Stress Gap Nominal Body Length (1/1000-Inch) -1
9 2 3
10 9
0 -1½
4 10 +1 5 11 +1½ (Relative Headspace)
Black Hills
Ammunition
Gun
Collections Wanted
Phone: 605-341-5211
Fax: 605-341-0431
strum@rapidcity.net
First Stop Guns 701 Main Street
Rapid City, SD 57701 Sightron Sport Optics Headquarters
die during full-length resizing. As noted, I used the RCBS Preci-
sion Mic to measure the length of each case body at each step of this process. With careful use of that tool, I expect measurement precision of about +/- ¼-thousandth-inch. For this study, this degree of measurement accuracy was marginal but sufficient.
Test #3 proved that resizing the
case body at first drives the case shoul- der forward (just as Wilson demonstrat- ed). This also proved that case-to-case variation in springiness is significant (otherwise each measurement change would be essentially identical for each
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164 |
Page 165 |
Page 166 |
Page 167 |
Page 168 |
Page 169 |
Page 170 |
Page 171 |
Page 172 |
Page 173 |
Page 174 |
Page 175 |
Page 176 |
Page 177 |
Page 178 |
Page 179 |
Page 180 |
Page 181 |
Page 182 |
Page 183 |
Page 184 |
Page 185 |
Page 186 |
Page 187 |
Page 188 |
Page 189 |
Page 190 |
Page 191 |
Page 192 |
Page 193 |
Page 194 |
Page 195 |
Page 196