Cartridge Case Head. In referring to this part of the case, it is intended to include that part of the body just in front of it where the side walls are thickest. Being the safety end of the cartridge, this part is worthy of the special attention of the rcloadcr. In addition to scaling in the gasses, it contains the primer pocket and flash hole, or
vent, and it is the part by which the case is extracted from the chamber. If a rimmed case, the rim serves to position the case in the chamber and affords a solid support to the blow of the firing pin, a more solid and sausfactory support, by the way, than the springy shoulder of the rimless case. Heads may be of the solid or the so called folded head types, the former predominate in present day ammunition, the latter being principally confined to revolver cartridge cases. Even in the latter there is a gradual swing toward the solid type of head, made necessary by the high speed loads with which some revolver cartridges are now being loaded. These loads develop pressures above the 15,000 lb. limit that is the acccptcd maximum for use in folded head eases and it is quite probable that in a few years time the folded head ease will become a thing of the past.
The thickness of solid heads will run uniform in any one lot of ammunition and generally in one make of a given caliber, but a considerable difference in the thickness of the heads, as well as in the thickness and taper of the side walls, may be found in different makes of the same caliber.
As the outside dimensions of these cartridges must be kept 22 the same, within dose manufacturing tolerances, any increase in the thickncss of the head or the side walls will result in a decrease in the volume of the eases. If two cases having different volumes are loaded with the same powder chargcs and bullets, the case with the least capacity will develop the higher pressure. With reduced or normal full charge loads, such a condition is not likely to be dangerous, but it might easily be a serious factor with maximum loads.
It has already been explained that chambers have a greater taper than the cartridges which go into them, in order to permit easy extraction, and that the taper varies in different types of arms of the same caliber. This sometimes results in a rather loose fit between cartridge and chamber at the head and permits a severe expansion of the case at the junction of its side walls and the head. This causes the metal in the solid head to tear apart for a short distance. If the case is resized completely, the torn metal will be pressed together, but the torn surfaces will not unite into a homogeneous structure. Upon firing the case again with a full or approximately a full charge, the same amount cf expansion will take place once more and the violcncc of the expansion will cause the brass to tear further. The illustration on Plate III shows such a condition. This is a photograph of a factory cartridge after the first firing and the dotted lines show the approximate form of, and the condition as it would apply to a rimless case. This condition is no joke and is worthy of the consideration of every careful reloader. The only practicable method of determining whether or not this condition exists is to examine the fired cases for expansion near the head and if the expansion appeared to be excessive, to sec
tion a few cases and look for torn metal in their solid heads. The correct method for doing this is described on page 31.
If heads tear in this way and the cases are not completely resized, when they arc reloaded and fired the case will be in close contact with the chamber walls because of the expansion that already has taken place, consequendy there will be very little or no further tearing of the brass in the solid head. Nevertheless, cartridge cases that expand excessively near the heads should not be reloaded with anything except reduced loads.
Primer pockets and vents, being closely related to the performance of primers, will be discussed under the subject of "primers" in Chapter 2.
The distance from the face to the rear of the locking lugs I» the most important dimension on a rifle bolt and is held very dose.
Split and ruptured cartridge eases.
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