Was just playing Call Of Duty and it got me wondering. Thanks in advance.
In: Engineering
No electricity required for small arms (human carried), but their accessories such as optics and illumination may require batteries. As a round is fired, in the fractions of a second before the bullet leaves the mouth of the barrel, guns can use the captive gas pressure that builds in the barrel behind the bullet. A small hole in the barrel let’s some of that pressure escape into a tube that routes the gas back to the bolt of the gun. For a split second the gas is under enough pressure to force the bolt of the gun backwards. This action ejects the spent case, and allows the gas to escape. A spring behind the bolt presses the bolt forward again and as this bolt returns to a closed position it lifts a new round into the chamber and resets the trigger.
In a semi-automatic gun (most guns today) the operator would pull the trigger once, one round is fired but this mechanical “action” sets the gun up for another round to be in a ready state to fire when the operator pulls the trigger a second time.
In a fully automatic gun or “automatic”, most commonly in military hands and illegal for civilian possession in the US without going through an onerous registration process and paying lots and lots of money (~$20k), holding down the trigger fires the weapon again as soon as the bolt closes on a new round. This speed commonly fires at many hundreds of rounds per minute, far faster than a human can actuate a trigger on a semi-auto.
This simple but ingenious mechanical “action” is very old tech (over 100 years) and can be applied to any firearms platform irrespective of how much “power” characterizes it. Small calibers such as .22’s employ these mechanics, as well as large .50 caliber crew weapons and large turret-mounted weapons. This style of cyclic action contrasts with the lever action, the bolt action, and the revolver to name a few examples which all require more mechanical manipulation to get a weapon ready to fire again.
Semi-auto and fully-auto actions are generally considered less accurate rifle platforms than bolt actions, but their rate of fire offers other advantages. As such, many of the higher power rifle platforms do not employ automatic bolt actions. For example, hunting rifles such as the .30-06 and the .45-70 are commonly in bolt action or lever action platforms and exceed the knock-down power of the most common semi-auto platforms on the market (.223 or handgun calibers). I mention this to emphasize that contrary to a popular perception, most gas-operated guns available today are not considered “high-powered” in the broad scope of gun design for which power is measured by sectional density, retained velocity, and effective range.
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