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Ok, so at the GTG I noticed that an astounding amount of people who shot the mac thought something was wrong with the gun when they put in a fresh mag, cocked the bolt, and the bolt remained open. I got a few "it wont cock" and "the bolt wont close", but after explaining that the gun fired from an open bolt all was well. Hell, I have been to a competition in BFE where the range officer was insistent upon me walking around the range with the gun's bolt open in the ready to fire position, even though I explained how the bolt closed with no mag in it is correct and how they do it at sub gun matches.
Anyways, here is a good run down on open bolt, how it works, and the advantages and disadvantages of the system-
A semi or full automatic firearm is said to fire from an open bolt if, when ready to fire, the bolt and working parts are held to the rear. When the trigger is pulled the bolt goes forward, feeding a round from the magazine into the chamber and firing it. Like any other self-loading design without an external power supply, the action is cycled by the energy of the shot; this sends the bolt back to the rear, ejecting the empty cartridge case and preparing for the next shot.
Advantages-
Fewer moving parts
The firing pin is usually part of the bolt
In automatic weapons an open bolt helps eliminate cook-off
Open bolt designs typically operate much cooler
Disadvantages-
The weapon is more prone to fire when dropped
Subject to picking up dirt
Open-bolt machine guns can not be synchronized to fire through the arc of a propeller
Accuracy can suffer somewhat in an open-bolt design, but this is generally less of a concern in automatic weapons. The large mass moving forward kicks the gun forward a bit on single shots.
A fixed firing pin on an open bolt gun can be seen here-
This is a cocked open bolt gun-
You can see that the firing pin is fixed forward, and then when cocked the bolt is clearly held open by a sear (the sear is very simple, its just a wedge that comes down to allow the bolt to spring forward. When the bolt slams forward, it feeds the round into the chamber and the firing pin slams into the primer in one smooth action.
A few guns that use this mechanism are-
American-180
AA-12 Shotgun
Browning Automatic Rifle
FN MAG and variants (including the M240)
FN Minimi and variants (including the M249)
Jatimatic
Lewis gun
M3
M60
MAC-10 & 11
MG34
MG42
MP40
RPD
Sten submachine gun
Sterling submachine gun
Thompson submachine gun
Uzi
Notice how many SMGs made the list.
Lastly, this may be the reason that many people are not too familiar with the system-
In the U.S., the ATF made a ruling in 1982 that semi-automatic open bolt weapons are readily convertible to fully automatic fire, therefore such weapons manufactured after the date of this ruling are classed and controlled as fully automatic weapons (weapons manufactured prior to the ruling are grandfathered and are still considered semi-automatic).
Thugs could take an over the counter mac 10 or tec-9 and easily (and I do mean easily) convert it to fire full auto, so they got banned. The "macs" and "uzis" you see today in stores fire from a modified closed bolt system that is so dissimilar from the weapons original design, it shares nothing in common aside from external appearance.
Anyways, hope this was interesting!
Anyways, here is a good run down on open bolt, how it works, and the advantages and disadvantages of the system-
A semi or full automatic firearm is said to fire from an open bolt if, when ready to fire, the bolt and working parts are held to the rear. When the trigger is pulled the bolt goes forward, feeding a round from the magazine into the chamber and firing it. Like any other self-loading design without an external power supply, the action is cycled by the energy of the shot; this sends the bolt back to the rear, ejecting the empty cartridge case and preparing for the next shot.
Advantages-
Fewer moving parts
The firing pin is usually part of the bolt
In automatic weapons an open bolt helps eliminate cook-off
Open bolt designs typically operate much cooler
Disadvantages-
The weapon is more prone to fire when dropped
Subject to picking up dirt
Open-bolt machine guns can not be synchronized to fire through the arc of a propeller
Accuracy can suffer somewhat in an open-bolt design, but this is generally less of a concern in automatic weapons. The large mass moving forward kicks the gun forward a bit on single shots.
A fixed firing pin on an open bolt gun can be seen here-
This is a cocked open bolt gun-
You can see that the firing pin is fixed forward, and then when cocked the bolt is clearly held open by a sear (the sear is very simple, its just a wedge that comes down to allow the bolt to spring forward. When the bolt slams forward, it feeds the round into the chamber and the firing pin slams into the primer in one smooth action.
A few guns that use this mechanism are-
American-180
AA-12 Shotgun
Browning Automatic Rifle
FN MAG and variants (including the M240)
FN Minimi and variants (including the M249)
Jatimatic
Lewis gun
M3
M60
MAC-10 & 11
MG34
MG42
MP40
RPD
Sten submachine gun
Sterling submachine gun
Thompson submachine gun
Uzi
Notice how many SMGs made the list.
Lastly, this may be the reason that many people are not too familiar with the system-
In the U.S., the ATF made a ruling in 1982 that semi-automatic open bolt weapons are readily convertible to fully automatic fire, therefore such weapons manufactured after the date of this ruling are classed and controlled as fully automatic weapons (weapons manufactured prior to the ruling are grandfathered and are still considered semi-automatic).
Thugs could take an over the counter mac 10 or tec-9 and easily (and I do mean easily) convert it to fire full auto, so they got banned. The "macs" and "uzis" you see today in stores fire from a modified closed bolt system that is so dissimilar from the weapons original design, it shares nothing in common aside from external appearance.
Anyways, hope this was interesting!
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