chamber pressure and the expansion of gas. The length of the barrel is impor- tant in relationship to velocity figures and generally, the longer the barrel the higher the velocity, up to a point. The word generally indicates this is not al- ways true, as will be explained. When the powder in the cartridge
is ignited, it expands as a hot gas, which in the open air would extend in all directions. This expansion, differing with various powders, can be as much as 800 to 1,300 times in the free air. The pressure accelerates the bullet down the barrel because it has no place else to go, discounting the leaks in some firearm types. The longer barrel won’t help, not
because the powder is still burning in the extended barrel, but because the gas is still expanding and pushing the bullet to a higher velocity. There may be some unburned powder found in the barrel after firing, but in that case, it probably would not have burned in any length of barrel. As the bullet moves down the
barrel, the area behind it is being filled as the expanding gas increases, but then the pressure eventually will be- gin to drop. There will be a point in an excessively long barrel where the drop in pressure would not be able to con- tinue acceleration against the friction required to push the bullet through the rifled bore. (Or a smooth bore, for that matter.) Also, a shock wave can develop at high gas velocity. At this point the ve- locity will begin to drop. Few firearms are made today with barrels excessively long, although weak ammunition can create this problem in an otherwise excellent gun. Example: The velocity of a .22
rimfire long rifle bullet will begin to slow at about a 16-inch to 18-inch barrel length, depending on ammunition type and firearm. At 16 inches, there is a gas expansion of about 37 times its original volume. The .22 has a tiny chamber and this gas expansion is extended to 44 if the barrel length is increased to 19 inches. The .22 short cartridge has an even smaller chamber and would give an even higher expansion in the same barrel length. Years ago, testing by Eric Johnson of Hoffman Arms Co. showed an 18-inch barrel length gave best ve- locity for the .22 long rifle cartridge. An interesting side point: The very
www.varminthunter.org Page 121
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high velocity of about 4,000 fps is hard to exceed in a .22 caliber regardless of powder charge because of the barrel’s resistance (friction) to the movement of both the bullet and the gas. Larger centerfires have a slightly higher limit. The barrel should have nothing in
it except the bullet and the push of the expanding gas. The combustion of the powder should all be in the cartridge case, not the barrel. That is why the statement that long barrels are best because they let all the powder burn is wrong. Barrel lengths are best at a
length (if practical) that lets the gas expansion be most efficient. As stated, combustion is best in the cartridge. The requirement for longer barrels
was stronger in black powder days than it is with modern powders. Today, the need for a long barrel for gas expansion is a fact but in earlier times this need included length for proper burning. Occasionally this persuades people in the present time to believe they need a barrel much longer than is required. Both ballistic laboratories and gun magazine writers have conducted many
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