which will average 1-inch groups, and it has definite value if you are shooting groups at 100 yards or small varmints at 175 yards with a firing system capable of averaging 0.5-inch groups. It is up to you to determine where you fit into this and take steps accordingly. The second objective of this evalu-
ation was to determine if rim thick- ness changed point of impact. This is of interest even if accuracy remained unchanged. For example, assume you shoot a five-shot group consisting of three cartridges having a 0.055" rim and two having a 0.060" rim. The three hav- ing a 0.055" rim could be very accurate and shoot a very small group and the two having a 0.060" rim could be equally accurate but impact some distance from the three-shot group – thus resulting in a larger group than would have resulted if five cartridges having equal rim thick- ness were used. Table 3 shows the location of the
center of all 12 groups using “x” and “y” coordinates. Table 4 shows the distances be-
tween the average locations of the group centers. It also shows that rim thickness
definitely changes point of impact – and by an amount slightly more than it changed accuracy. Table 2 shows a maximum change in accuracy of 0.166 inch (0.703 minus 0.537) and Table 4
shows a maximum point of impact change of 0.22 inch (between groups shot with 0.064 rims and 0.055 rims). The value of these changes in impact are essentially the same as those covered in detail concerning the value of accuracy changes (located in the last paragraph on page 137 and top-left paragraph on this page).
Considering all of the above con-
cerning rim thickness, general recom- mendations for those of you who have an accurate Hornet and want to maxi- mize its accuracy are as follows: 1. Throw away all cases having
a rim thickness less than 0.058 inch (or keep them for fouling and other endeav- ors not requiring accuracy). 2. Sort cases by rim thickness
with a spread of not more than 0.002 inch. For example, 0.058 through 0.060 inch, to gain substantial accuracy im- provement. 3. Throw away all cases having
a rim thickness more than 0.065 inch (or keep them if you can accumulate enough to be useful and if they will chamber in your rifle). 4. Select cases having a rim thick-
ness from 0.059 through 0.064 inch and then sort them into groups having a spread of 0.001 inch for maximum ac- curacy improvement. I would expect the same general results for other rimmed cartridges such
TABLE 3
Group Locations 0.055 Rim
Group 1 Group 2 Group 3 Group 4
Average location of group centers
x = 0.08 y= 0.14 x= 0.27 y= 0.01 x= 0.29 y= 0.03 x= 0.42 y= 0.20 x= 0.26 y= 0.10
TABLE 4 Groups
0.055 Rim and 0.060 Rim 0.060 Rim and 0.064 Rim 0.064 Rim and 0.055 Rim Average
Page 138 Spring 2012
Distance Between Average Location Of Group Centers
0.14" 0.17" 0.22" 0.18"
0.060 Rim 0.064 Rim
x = 0.09 x = 0.12 y= 0.38 y= -0.17 x= 0.01 x= 0.42 y= -0.07 y= -0.26 x= 0.27 x= 0.22 y= -0.21 y= 0.0 x= 0.18 x= 0.18 y= 0.0 y= -0.04 x= 0.14 x= 0.24 y= 0.02 y= -0.12
as the 218 Bee, the 219 Donaldson Wasp, the 219 Zipper, etc. The 22 “K” Hornet and other “improved” rimmed car- tridges are also candidates unless you are doing an excellent job of headspac- ing on their shoulders. Earlier I discussed the possibility
of Case Head Separation (CHS) on the Hornet cases having a rim thickness of 0.055". You may want to reread this sec- tion if you did not previously form an opinion. Do you now have an opinion? Are you ready? Here goes. My RCBS Case Master Tool gave absolutely no indication of any CHS on any of the cases having 0.055" rims. I partially sec- tioned one of them (see photo on page 136) and could see no indication of any CHS. Based on this, we must conclude that the elastic limit of the case material was not exceeded in the area where CHS normally takes place. This is backed up by the fact that all primers in these fired 0.055" rim cases remained backed out of the primer pockets an average of 0.0064" (a minimum of 0.002" and a maximum of 0.009"). One of the reloading steps I always
follow is to check for CHS on approxi- mately 20 percent of the fired cases in a group. Assuming no CHS, I proceed with case preparation. Assuming that some amount of CHS is detected, more cases are checked and the appropriate action is then taken. Appropriate action generally includes disposing of all cases having more than 0.003 inch of CHS or the entire group if numerous cases have CHS greater than 0.003 inch. This is not a recommendation for anyone else to follow – it only outlines what I generally do. The fact that CHS did not start
or occur in the 0.055" rim cases did not surprise me. I have numerous cases with a 0.058" rim thickness which have been fired seven or more times and show no indication of any CHS. Without this knowledge, I probably would have guessed the beginning of CHS in the 0.055" rim cases. I wonder if a some- what hotter load would result in some amount of CHS? I hope some of the above assists
you in improving accuracy from one of the most shooter friendly and “most fun to shoot” cartridges available – the 22 Hornet.
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