rifle primers, to prevent primer piercing or blanking. Discoloration of primer- cup striker indentation indicates a gas leak resulting from the striker punching through the cup. Blanking, or partial blanking, occurs when the portion of the primer under the striker completely or partially extrudes into the firing pin hole in the bolt face (this is often incorrectly referred to as cratering). Piercing usually results from an
unnecessarily robust striker impact and is common in the Hornet because gun manufacturers often use the same striker system used for cartridges that should always use rifle primers. That was the case with the tested CZ before I altered it to reduce striker force. Blanking can result from a rela-
tively light striker or where the firing- pin hole in the bolt face is significantly larger than the striker tip. If your gun demonstrates either
problem, either gunsmithing is in order or a substitution to a mild rifle primer is required. If you prefer not to improve the gun or improvement is infeasible, the WSR is likely to be a good alterna- tive primer.
Cases used I obtained new R-P cases for this
study, which was no mean feat! I pur- chased 1,000 of one lot. I sorted those into 0.2-grain groups. The following indicates measured mass distribution. Excluding nineteen outliers (seven
cases lighter than 44.9 and twelve cases heavier than 46.0), average mass of cases in this batch was very close to 45.54 grains. All remaining cases fall within a weight range of 1.1 grains. The indiscriminate use of these in any given load would introduce a maximum of 18 fps velocity variation. Considering the relatively limited ranging poten- tial of the Hornet, this would seem a rather insignificant matter. However, to minimize uncontrolled variables in this testing I used only cases in the 45.7- to 45.8-grain set. Cases in one recent lot from Rem-
ington are, on average, significantly lighter than 45 grains. Case weight in that lot seems to be unusually consistent (too bad I lacked enough of those cases to do this testing). Winchester cases commonly aver-
age about 50 grains and sometimes as much as 54 grains. Those have between about one-half and about one grain less
APPROXIMATE CHARGE AND VELOCITY DIFFERENCES (CASES OF DIFFERENT WEIGHT LOADED TO SAME PRESSURE) CASE
CASE FILLING RATIO PERCENTAGE
WEIGHT (grains)
45 50 55 60 65
(VOLUME UNDER SEATED BULLET OCCUPIED BY CHARGE) CORRECTION (GR.) | FPS DIFFERENCE
< 60% — | —
-0.15 | -25 -0.30 | -50 -0.50 | -75 -0.60 | -100
60% - 80% — | —
-0.20 | -26 -0.45 | -52 -0.70 | -78 -0.80 | -104
capacity and will require between about three-tenths and six-tenths grain charge reduction, to give the same pressure as the loads presented here (using 45-grain Remington cases). Some European-made cases weigh
significantly more than 55 grains; those will require a greater charge reduction. The following table suggests approxi- mate charge adjustments, to account for variations in case weight, while main- taining similar peak chamber pressure. With best propellants and with
charges adjusted to produce the same peak chamber pressure, the greater capacity of Remington cases (compared to Winchester cases) will add about 10 yards to usable range. When I started playing with the Hornet, this seemed a worthwhile advantage. Now I am not so sure that I would not prefer the heavier Winchester cases, which have thicker rims, thicker necks, and thicker case walls, all of which are apt to improve both accuracy and case life. As with charge precision, the
smaller the case volume the greater the consequences of variations. To minimize velocity variation, those interested in maximum Hornet performance and accuracy should sort cases into weight groups of plus-or-minus three-tenths grain. When feasible, purchase all needed cases from one production lot. Chamber Variation
Chiefly because of headspace variation, Hornet chambers vary sig-
80% -100% — | —
-0.25 | -27 -0.55 | -55 -0.80 | -85 -1.00 | -108
>100% — | —
-0.30 | -30 -0.60 | -60 -0.95 | -90 -1.25 | -120
nificantly. In the test gun, fired cases that weigh 45 grains (without primer) hold 14.9 grains of water, full to the case mouth, with a flat meniscus. Before using any of these data, compare your chamber by measuring capacity of a fired, primed case, as follows: Measure and record case weight. Fill case with water so that it forms a flat meniscus at the case mouth (assure that no air bubbles are trapped in case); measure and record weight of water-filled case; subtracting weight of primed case from weight of water-filled, primed case gives case volume in grains of water ((case + water) – case = water). Use the following table (at bottom
of page) to correct for difference in ca- pacity between your tested case and a standard 45-grain case (as used for the data represented in this article). For cases lighter than 45 grains,
reduce measured capacity to get equiva- lent capacity of your chamber. For cases heavier than 45 grains, increase mea- sured capacity to get equivalent capacity of your chamber. Then use the following table to
adjust charges presented in this article to give similar pressure in your gun. Everything else being equal, adjusted charges would give indicated velocity difference. For chamber resulting in a case
holding less than 14.9-grains, reduce charge to get equivalent pressure (but less velocity). For chamber resulting in
WEIGHT OF YOUR CASES (GRAINS) | CAPACITY CORRECTION FACTOR TO EQUAL CAPACITY OF 45-GRAIN CASE IN TESTED CHAMBER
41.62 | -0.4 42.47 | -0.3 43.31 | -0.2 44.16 | -0.1 45.00 | -0.0
45.85 | +0.1 46.69 | +0.2 47.54 | +0.3 48.38 | +0.4 49.23 | +0.5
50.92 | +0.6 51.76 | +0.7 52.61 | +0.8 53.45 | +0.9 54.30 | +1.0
55.14 | +1.1 55.99 | +1.2 56.83 | +1.3 57.68 | +1.4 58.52 | +1.5
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