From the 05/05/07 draft of the Third Edition of M14 Rifle History and Development by Lee Emerson copyright 2007:
"Safety - Designed as a military weapon, the M14 type rifle has a number of safety features that protect the operator or unintended targets from injury. Some of these features are common to other firearms while the remainder are M14 specific. In order to fire, the USGI M14 rifle must be assembled, the magazine loaded with at least one cartridge and inserted into the rifle, the hammer cocked by pulling the operating rod to the rear with at least 15.31 pounds of force, the bolt stripping a cartridge from the magazine and fully closing into battery, the safety disengaged and the operator pulling the trigger to the rear with sufficient force, typically 5.5 to 7.5 pounds, before the bullet will exit the barrel. It takes several deliberate physical acts by a human operator to cause the M14 type rifle to discharge a bullet.
The receiver bridge with its camming surface and cutout work together with the tang of the firing pin to: 1) mechanically retract the firing pin when the bolt rotates to unlock after firing, preventing a "sticky", rusted or gummed-up firing pin from remaining in the forward position during the rest of the cycle of operation 2) prevent the firing pin from slamming forward when the round being loaded stops in the chamber, preventing a "slam fire" while the bolt is still unlocked. The firing pin can travel forward through the bridge cutout only after the bolt has fully closed and locked. Additionally, the hammer cocking machining cut on the rear end of the bolt prevents the hammer from striking the firing pin until the bolt lugs have rotated into locked position.
The sear engages the hammer to prevent firing until sufficient force is applied to the trigger by the operator. The hammer spring and hammer work together to prevent the primer from blowing out of the cartridge case once the gunpowder has ignited. An easily operated safety can be engaged to prevent any rearward movement of the trigger and any forward motion of the hammer whatsoever. With the safety engaged, the trigger is disengaged from the hammer and the trigger is limited in its rearward travel. The engaged safety rests on top of the hammer left side ridge, positively preventing a strike on the firing pin. The trigger guard aids in unintended discharge of the rifle by limiting access to the trigger. The two stage trigger pull gives the operator sufficient pause for getting the sights on target or for choosing not to engage at the last twinkling.
When the gun powder inside the cartridge case ignites the hot propellant gas generates a chamber pressure of 50,000 psi or more. The chamber pressure is prevented from venting into the operator’s face by the locking action of the bolt and receiver lugs. As the gas pressure acts on the gas system, the operating rod will move about 5/64 " to the rear before engaging the bolt to rotate and unlock. This allows sufficient time for propellant gas pressure inside the barrel to drop to ambient pressure. The cutoff and expansion gas system of the M14 develops less gas cylinder pressure than the impingement gas system of the M1. From a safety standpoint, this results in less force acting on the operating rod as it moves to the rear. Less force pushing on the operating rod means softer impact on the receiver by the bolt. The "hump" of the operating rod, located just in front of the handle, serves to knock the ejected cartridge case to the right and forward of the shooter, typically 1 o’clock to 2 o’clock as viewed looking down range along the barrel. This ejection pattern minimizes the risk from hot cartridge brass to adjacent shooters. After the last cartridge has been ejected from the rifle the bolt lock will engage the bolt holding it to the rear. This feature is a visual indicator that the rifle is out of ammunition.
Should several things go terribly wrong and the rifle fires before the bolt lugs have engaged the receiver, the propellant gas will vent forward through the barrel and downward into the magazine well and outward through the gap between the receiver and the stock. The rearward movement of the bolt is controlled by the force of the operating rod spring and the receiver safety lug. As the bolt moves rearward it is forced downward by the slope of the receiver heel. Some commercial M14 type receivers have well defined bolt raceways aft of the receiver bridge which further aids the downward movement of the bolt upon opening.
The hand guard prevents operator injury from the hot barrel. The foam filled USGI M14 synthetic stock helps to minimize hearing loss by dampening vibration to the operator’s skull when firing. Note that this is no substitute though for proper hearing protection. Automatic fire is possible with M14 rifles built with functional select fire components and only when the selector switch has been turned to the automatic fire position. Otherwise, the rifle will only discharge once for each rearward pull of the trigger."
"Safety - Designed as a military weapon, the M14 type rifle has a number of safety features that protect the operator or unintended targets from injury. Some of these features are common to other firearms while the remainder are M14 specific. In order to fire, the USGI M14 rifle must be assembled, the magazine loaded with at least one cartridge and inserted into the rifle, the hammer cocked by pulling the operating rod to the rear with at least 15.31 pounds of force, the bolt stripping a cartridge from the magazine and fully closing into battery, the safety disengaged and the operator pulling the trigger to the rear with sufficient force, typically 5.5 to 7.5 pounds, before the bullet will exit the barrel. It takes several deliberate physical acts by a human operator to cause the M14 type rifle to discharge a bullet.
The receiver bridge with its camming surface and cutout work together with the tang of the firing pin to: 1) mechanically retract the firing pin when the bolt rotates to unlock after firing, preventing a "sticky", rusted or gummed-up firing pin from remaining in the forward position during the rest of the cycle of operation 2) prevent the firing pin from slamming forward when the round being loaded stops in the chamber, preventing a "slam fire" while the bolt is still unlocked. The firing pin can travel forward through the bridge cutout only after the bolt has fully closed and locked. Additionally, the hammer cocking machining cut on the rear end of the bolt prevents the hammer from striking the firing pin until the bolt lugs have rotated into locked position.
The sear engages the hammer to prevent firing until sufficient force is applied to the trigger by the operator. The hammer spring and hammer work together to prevent the primer from blowing out of the cartridge case once the gunpowder has ignited. An easily operated safety can be engaged to prevent any rearward movement of the trigger and any forward motion of the hammer whatsoever. With the safety engaged, the trigger is disengaged from the hammer and the trigger is limited in its rearward travel. The engaged safety rests on top of the hammer left side ridge, positively preventing a strike on the firing pin. The trigger guard aids in unintended discharge of the rifle by limiting access to the trigger. The two stage trigger pull gives the operator sufficient pause for getting the sights on target or for choosing not to engage at the last twinkling.
When the gun powder inside the cartridge case ignites the hot propellant gas generates a chamber pressure of 50,000 psi or more. The chamber pressure is prevented from venting into the operator’s face by the locking action of the bolt and receiver lugs. As the gas pressure acts on the gas system, the operating rod will move about 5/64 " to the rear before engaging the bolt to rotate and unlock. This allows sufficient time for propellant gas pressure inside the barrel to drop to ambient pressure. The cutoff and expansion gas system of the M14 develops less gas cylinder pressure than the impingement gas system of the M1. From a safety standpoint, this results in less force acting on the operating rod as it moves to the rear. Less force pushing on the operating rod means softer impact on the receiver by the bolt. The "hump" of the operating rod, located just in front of the handle, serves to knock the ejected cartridge case to the right and forward of the shooter, typically 1 o’clock to 2 o’clock as viewed looking down range along the barrel. This ejection pattern minimizes the risk from hot cartridge brass to adjacent shooters. After the last cartridge has been ejected from the rifle the bolt lock will engage the bolt holding it to the rear. This feature is a visual indicator that the rifle is out of ammunition.
Should several things go terribly wrong and the rifle fires before the bolt lugs have engaged the receiver, the propellant gas will vent forward through the barrel and downward into the magazine well and outward through the gap between the receiver and the stock. The rearward movement of the bolt is controlled by the force of the operating rod spring and the receiver safety lug. As the bolt moves rearward it is forced downward by the slope of the receiver heel. Some commercial M14 type receivers have well defined bolt raceways aft of the receiver bridge which further aids the downward movement of the bolt upon opening.
The hand guard prevents operator injury from the hot barrel. The foam filled USGI M14 synthetic stock helps to minimize hearing loss by dampening vibration to the operator’s skull when firing. Note that this is no substitute though for proper hearing protection. Automatic fire is possible with M14 rifles built with functional select fire components and only when the selector switch has been turned to the automatic fire position. Otherwise, the rifle will only discharge once for each rearward pull of the trigger."
