Rifleman1776
New member
At one time I read about a single shot recoiless rifle being made that shot from an open bolt. Interesting but I have no idea how a gun can be shot with the bolt open.
Please enlighten me.
Please enlighten me.
what does open bolt mean?
- Thread starter Rifleman1776
- Start date
Brian Pfleuger
Moderator Emeritus
Open bolt single shot? I guess it must be associated with the "recoilless" part somehow. I am under the impression that open bolt is almost always associated with full-auto weapons.
Most SMGs fire from an open bolt.Pulling the trigger releases the bolt which goes forward and ignites the cartridge .The H&K MP5 fires from a closed bolt.
The problem with a full auto gun is that the parts can get hot enough to ignite a cartridge just from the heat alone .To prevent this the open bolt system also has no cartridge in the chamber .
The problem with a full auto gun is that the parts can get hot enough to ignite a cartridge just from the heat alone .To prevent this the open bolt system also has no cartridge in the chamber .
carguychris
New member
FWIW Winchester briefly made a single-shot .22LR rifle in the 1960s, the Model 55*, which operated like a semi-auto without the magazine. I've never used one, but from what I understand regarding the gun's operation, the bolt locked open after firing, the shooter inserted a fresh cartridge, the shooter released the "safety", thereby releasing the bolt, the shooter fired, and the process was repeated. IIRC the gun was a spectacular marketing failure and was discontinued after only 2 years, although it was offered for a 3rd year at a drastically discounted price to clear out Winchester's inventory. I think it was the answer to a question nobody was asking.
Regarding the OP's question, I've heard of several light artillery pieces, mostly AAA guns, that used this method of operation. AFAIK the purpose was twofold: (a) to allow the loader to more easily insert a fresh round into the hot breech and (b) to force manual loading and thereby slow down the crew's rate of fire. Excessively fast firing can overheat the gun, reducing barrel life and causing rounds to "cook off", and it was thought that slowing down the rate of fire would encourage crews to aim carefully instead of dumping all their ammunition downrange at the first sign of trouble- similar to the thinking that caused many armies to resist semi-auto and selective-fire infantry rifles for so long.
*Not to be confused with the earlier Model 55, which IIRC was a 1930s-vintage budget .30-30 Model 92 variant with a 3rd magazine and a less finely-finished stock.
Beowulf5505
New member
hmm.. a recoilless rifle does not really have a "bolt" as one would see on a regular gun. they are single shot jobs.
http://en.wikipedia.org/wiki/Recoilless_rifle
as stated above open bolts are generally for full auto weapons. semi auto open bolts are not easily available in the us because they are too easy to convert to full auto
http://en.wikipedia.org/wiki/Recoilless_rifle
as stated above open bolts are generally for full auto weapons. semi auto open bolts are not easily available in the us because they are too easy to convert to full auto
I've never heard of a single shot open bolt, but that doesn't mean there isn't one but I see no purpose in it. Usually an open bolt is pretty much as described above with the bolt being open and when you pull the trigger the bolt loads a round and fires and then opens like a normal semi auto would with an empty clip and remains open. Pull the trigger again and it loads and fires again and goes back to the hold open. The firing pin is fixed, like a nail welded to the bolt face. The idea is fewer parts making it usually a very reliable weapon. The bolt acts as firing pin and hammer as a unit activated by the release of the unit by the trigger sear. The bolt spring is the power behind the unit. The Tommy Gun or Thompson machine rifle was an open bolt design, for reference.
While many designs (particularly post WWII ones) do have fixed firing pins, many open bolt guns (and all the semis) do not.
Back in the early 80s, there were several "pistols" you could get, basically semi auto copies of SMGs, and they fired from the open bolt. There was also a single shot, open bolt shotgun from one of those makers.
The BATF took them to court, claiming that open bolt guns were too "easy" to convert to full auto. I don't remember anybody going to jail, but all those open bolt guns went away. The pistols came back, redesigned to fire from the closed bolt. And as a semi auto pistol, they were better for it. But they are still lousy pistols, being bigger and much more awkward than a regular duty style semi auto. Neat to play with, not so good for any serious use.
The main problem with open bolt semiautos (besides the strong govt objection) is the fact that the mass of the bolt closing tends to throw off one's aim. With a SMG, thats not all that important, but when firing individual shots from a semi auto, it makes a big difference.
Back in the early 80s, there were several "pistols" you could get, basically semi auto copies of SMGs, and they fired from the open bolt. There was also a single shot, open bolt shotgun from one of those makers.
The BATF took them to court, claiming that open bolt guns were too "easy" to convert to full auto. I don't remember anybody going to jail, but all those open bolt guns went away. The pistols came back, redesigned to fire from the closed bolt. And as a semi auto pistol, they were better for it. But they are still lousy pistols, being bigger and much more awkward than a regular duty style semi auto. Neat to play with, not so good for any serious use.
The main problem with open bolt semiautos (besides the strong govt objection) is the fact that the mass of the bolt closing tends to throw off one's aim. With a SMG, thats not all that important, but when firing individual shots from a semi auto, it makes a big difference.
An "open-bolt" firearm is simply one that has the bolt carrier, in the case of the AR, the BCG, exposed during the period of operation, thus exposed or open. You can see it on the ejection port, for example, the AR, AK, MP, etc. A closed-bolt refers to weapons such as a bolt-action M1 or any lever-action or bolt-action mechanism, where the cycling encloses the action of the firing mechanism as well as enclosing the action of chambering the following round. The only time the bolt is exposed is because of the operator pulling the BCG manually out of the chamber, expelling the spent casing and chambering the next round, thereby "closing" the bolt again during firing operation.
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DAVID NANCARROW
New member
Most SMGs fire from an open bolt.Pulling the trigger releases the bolt which goes forward and ignites the cartridge .The H&K MP5 fires from a closed bolt.
The problem with a full auto gun is that the parts can get hot enough to ignite a cartridge just from the heat alone .To prevent this the open bolt system also has no cartridge in the chamber .
Exactly. Mete has it correct.
The problem with a full auto gun is that the parts can get hot enough to ignite a cartridge just from the heat alone .To prevent this the open bolt system also has no cartridge in the chamber .
Exactly. Mete has it correct.
Rifleman1776
New member
Very interesting.
So 'open bolts' do not fire from an open bolt. They close and fire then open.
So 'open bolts' do not fire from an open bolt. They close and fire then open.
DAVID NANCARROW
New member
No AR I ever fired in the military fired from an open bolt
thesheepdog
New member
Some AR's out there (LWRC to be exact) have a LMG model that fires from an open bolt.
OPen bolt just basically means-and as posted earlier-that the bolt is open. When you pull the trigger, you're releasing the bolt and the blowback locks the bolt back open after the gin is fired (semi-auto)
With heavy machine guns, they ususally get very hot during operation, and a fresh round in a red-hot chamber is a bad idea (could lead to blowing up a barrel)
Think of it like this: It's backwards from your normal semi-auto weapons-where the bolt is closed until the trigger is pulled.
You lose accuracy with open bolt designs, but you're a lot safer when heating up the barrel.
OPen bolt just basically means-and as posted earlier-that the bolt is open. When you pull the trigger, you're releasing the bolt and the blowback locks the bolt back open after the gin is fired (semi-auto)
With heavy machine guns, they ususally get very hot during operation, and a fresh round in a red-hot chamber is a bad idea (could lead to blowing up a barrel)
Think of it like this: It's backwards from your normal semi-auto weapons-where the bolt is closed until the trigger is pulled.
You lose accuracy with open bolt designs, but you're a lot safer when heating up the barrel.
Once again, c_jackson, you are in error.
This definition is incorrect, and totally at odds with the description and definition found in standard reference works for generations.
"open bolt" does not refer to being able to see the bolt or bolt carrier group through the ejection port. The AR, AK, MP, are NOT OPEN BOLT GUNS!!!
The terms "open bolt" and "closed bolt" refer to the position of the bolt when the firing cycle is intitiated. In other words, where the bolt is when the trigger is pulled.
Fully loaded and ready to fire, the open bolt gun has rounds in the magazine (or belt), the bolt is to the rear, and the chamber is empty. When the trigger is pulled, the bolt is released, drives forward under spring tension, feeds a round into the chamber and fires it. After extracting and ejecting the fired case, the bolt remains held to the rear (chamber empty) until the trigger is pulled again (semi), or the trigger held back (full auto) it repeats the cycle, going forward, loading the chamber firing, extracting, and ejecting the fired case. In a full auto this cycle continues as long as the trigger is held, and ammunition remains to be fed. When the trigger is released, the bolt is held to the rear (open).
This is the exact opposite of a closed bolt gun. In a closed bolt gun (like the AR, AK, MP5, etc.) to make the gun ready for firing, the bolt is pulled back and released, where it then moves forward, chambering a round (independant of the trigger position). The chamber is loaded, and the bolt is closed. Pulling the trigger fires the gun, and the bolt opens, extracts and ejects the fired case, then feeds another round into the chamber, and remain closed, waiting for the next trigger pull (semi), or firing the next round (trigger held back, full auto) to repeat the cycle.
Open bolt operation is found on many submachineguns, and belt fed machineguns. Its purpose is to enhance cooling of the gun, by allowing air to circulate in the chamber at all times when not actually firing. Keeping the chamber empty, except when actually firing also prevents "cook off" of a chambered round.
The AR, AK, M1, M14, FAL, G3, M1Carbine, and many others are all closed bolt weapons. So is the H&K MP5, which makes it s rarity among submachineguns. The Tommy gun, M3 Grease gun, Sten gun, MP40, PPsh and most other submachineguns are open bolt weapons.
The terms open and closed bolt are only applied to semi/full automatic actions. They are not applied to manually operated actions. There is no such thing as an open, or closed bolt lever action, pump, or bolt action. The terms simply do not apply.
I was a Small Arms Repairman (MOS 45B20) for several years in the US Army, trained at the USAOC&S, Aberdeen Proving Grounds, MD. I worked on many open and closed bolt weapons during my time in service, and have a thorough and correct understanding of the terms and their application.
c_jackson is wrong, his information is not accurate. Period. If you have any further questions, ask.
This definition is incorrect, and totally at odds with the description and definition found in standard reference works for generations.
"open bolt" does not refer to being able to see the bolt or bolt carrier group through the ejection port. The AR, AK, MP, are NOT OPEN BOLT GUNS!!!
The terms "open bolt" and "closed bolt" refer to the position of the bolt when the firing cycle is intitiated. In other words, where the bolt is when the trigger is pulled.
Fully loaded and ready to fire, the open bolt gun has rounds in the magazine (or belt), the bolt is to the rear, and the chamber is empty. When the trigger is pulled, the bolt is released, drives forward under spring tension, feeds a round into the chamber and fires it. After extracting and ejecting the fired case, the bolt remains held to the rear (chamber empty) until the trigger is pulled again (semi), or the trigger held back (full auto) it repeats the cycle, going forward, loading the chamber firing, extracting, and ejecting the fired case. In a full auto this cycle continues as long as the trigger is held, and ammunition remains to be fed. When the trigger is released, the bolt is held to the rear (open).
This is the exact opposite of a closed bolt gun. In a closed bolt gun (like the AR, AK, MP5, etc.) to make the gun ready for firing, the bolt is pulled back and released, where it then moves forward, chambering a round (independant of the trigger position). The chamber is loaded, and the bolt is closed. Pulling the trigger fires the gun, and the bolt opens, extracts and ejects the fired case, then feeds another round into the chamber, and remain closed, waiting for the next trigger pull (semi), or firing the next round (trigger held back, full auto) to repeat the cycle.
Open bolt operation is found on many submachineguns, and belt fed machineguns. Its purpose is to enhance cooling of the gun, by allowing air to circulate in the chamber at all times when not actually firing. Keeping the chamber empty, except when actually firing also prevents "cook off" of a chambered round.
The AR, AK, M1, M14, FAL, G3, M1Carbine, and many others are all closed bolt weapons. So is the H&K MP5, which makes it s rarity among submachineguns. The Tommy gun, M3 Grease gun, Sten gun, MP40, PPsh and most other submachineguns are open bolt weapons.
The terms open and closed bolt are only applied to semi/full automatic actions. They are not applied to manually operated actions. There is no such thing as an open, or closed bolt lever action, pump, or bolt action. The terms simply do not apply.
I was a Small Arms Repairman (MOS 45B20) for several years in the US Army, trained at the USAOC&S, Aberdeen Proving Grounds, MD. I worked on many open and closed bolt weapons during my time in service, and have a thorough and correct understanding of the terms and their application.
c_jackson is wrong, his information is not accurate. Period. If you have any further questions, ask.
jaguarxk120
New member
One of the classic open bolt SMG's was the 45 cal M3, the only machined piece was the bolt everything else was stamped. I think the major cortractor building them during the war was (WWII) General Motors.
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Open bolt guns also have safety issues that you need to pay attention to, or things can get hairy.
First and foremost, to most people unfamiliar with them, the gun "looks" safe, as the bolt is open, "locked" to the rear. Its the one action where "open and safe" isnt.
When you unload them, you have to remove the mag first, then lower the bolt. Sounds silly, but you'd be amazed at how many people will try to lower the bolt with a loaded mag in the gun. Loading the gun (for the most part) requires the bolt to be down before the mag is inserted. If it can be locked, it should be.
You have to be careful when cocking the gun. Once that bolt is drawn to the rear and passes the top round on the mag, its game on. If your hand slips from the charging handle before the sear catches, the gun can, and probably will fire. If your finger happens to be on the trigger, it gets even more exciting.
Many of theses type guns are not drop safe. Most, but not all, have safety devices of some sort that will lock the bolt, but they are no guarantee, and you need to careful in your handling of them. If the gun goes down, all the bolt needs do, is move rearward far enough to strip a round. You also have to be careful with some of them when carrying them when cocked. A sudden jar can cause them to fire.
If youre shooting the gun and it stops, you have to make sure your finger comes off the trigger. In the rare instance you might have a hang fire and your finger is still on the trigger, the gun will start to run again once the round does go off.
First and foremost, to most people unfamiliar with them, the gun "looks" safe, as the bolt is open, "locked" to the rear. Its the one action where "open and safe" isnt.
When you unload them, you have to remove the mag first, then lower the bolt. Sounds silly, but you'd be amazed at how many people will try to lower the bolt with a loaded mag in the gun. Loading the gun (for the most part) requires the bolt to be down before the mag is inserted. If it can be locked, it should be.
You have to be careful when cocking the gun. Once that bolt is drawn to the rear and passes the top round on the mag, its game on. If your hand slips from the charging handle before the sear catches, the gun can, and probably will fire. If your finger happens to be on the trigger, it gets even more exciting.
Many of theses type guns are not drop safe. Most, but not all, have safety devices of some sort that will lock the bolt, but they are no guarantee, and you need to careful in your handling of them. If the gun goes down, all the bolt needs do, is move rearward far enough to strip a round. You also have to be careful with some of them when carrying them when cocked. A sudden jar can cause them to fire.
If youre shooting the gun and it stops, you have to make sure your finger comes off the trigger. In the rare instance you might have a hang fire and your finger is still on the trigger, the gun will start to run again once the round does go off.