|As robust as the cal..30 Browning machine guns are, they are not immune to malfunction. I came upon this 1953 printing of the TM9-2210 SMALL ARMS ACCIDENTS MALFUNCTIONS AND THEIR CAUSES and thought the section on the cal..30 machine guns worth sharing.|
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CAL. .30 MACHINE GUNS
Section 1. GENERAL
54. Operating Instructions
Section 11. PRECAUTIONARY MEASURES
55. Maintenance and Inspection
56. Danger Points
Section 111. EFFECTS AND PROBABLE CAUSES OF ACCIDENTS AND MALFUNCTIONS
58. Typical Cases
Case "3" in figure 23 is that of a standard ball cartridge fired in a gun having
Y4-inch excess head space. Note the shortened neck and the separation of the
ease approximately one-half inch from the head.
(c) Case "4" in figure 23 shows the effect of firing a high pressure cartridge in a gun having Y16-inch excess head space. Note evidence of excessive head space in the separation approximately one-half inch from the head of the case and in the shortened neck. Also, note evidence of high pressure in the heavy marking of the case by the chamber wall and in the relative sharpness of the newly formed shoulder crest joining the first and second cones.
b. Defective Ammunition.
|(1) An obstruction in the bore immediately forward of the chambered round may rupture the head of the cartridge case (fig. 27). An obstruction in the long middle portion of the bore may bulge the barrel at the point of the obstruction. If the resistance is sufficiently great, the bulge may become a rupture (fig. 29). An obstruction near the muzzle may bulge or split the barrel at the point of the obstruction.|
|(2) A bullet lodged in the bore immediately forward of the chambered cartridge will rupture the head of the cartridge case (fig. 28). A bullet lodged in the middle portion of the bore ordinarily does not rupture the fired case. The case may show signs of high pressure. Ordinarily, the rupture of the case head of the chambered round will ignite the cartridge lying directly above in the feedway. Typical damage from these explosions consists of a fractured "T" slot, a cracked or broken extractor, and a bent cover.|
Grease or heavy oil in the chamber invariably produces a flute in the fired
case (fig. 30). Note the characteristically elongated and radially contoured
shape of these flutes. Case heads will show some indications of high pressure.
Figure 30 also shows damage to the gun which commonly results from firing with
grease in both the chamber and the breech end of the bore. The high pressure
ruptures the case head, releasing the powder gases into the action. Note the
fractured "T" slot, cracked barrel extension, and bent cover.
d. Fractured Firing Pin.
Figure 31 exhibits damage to a gun caused by premature firing of the incoming round by a fractured firing pin. This typical accident was caused by fracture of the firing pin during counterrecoil. The firing pin spring drove the firing pin point prematurely into the primer of the incoming round. The explosion of the cartridge chipped the "T" slot and bent the cover upward.
e. Short Barrel-Plunger Spring. Some difficulty has arisen from a change that was made in the length of the barrel plunger spring for cal..30 machine guns. Springs for these guns manufactured prior to 1941 were longer than those manufactured for the weapons after that date, and the new-type shorter springs functioned satisfactorily in the old weapons except for a decreased rate of fire. The specification given in TM 9-1205 did not indicate the changed length but have since been revised to show the shorter barrel plunger spring length.