bushmaster1313
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Handguns seem to work just fine on the blowback principle.
Why not a blowback .223?
Why not a blowback .223?
Why not a blowback .223 semi-auto rifle?
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The same principle applies with rifles as with pistols. Blowback works well for lighter calibers but it becomes impractical with heavier calibers. The bolt weight and recoil spring tension have to rise to impractical values once the caliber goes past a certain power level.
handguns operate at MUCH lower pressures than rifles do....
the blowback pistols use very heavy slides to tame the forces (look at Hipoint).....to do that with a rifle, youd need a ridiculously heavy bolt.....its physically possible, just not practical
the blowback pistols use very heavy slides to tame the forces (look at Hipoint).....to do that with a rifle, youd need a ridiculously heavy bolt.....its physically possible, just not practical
bushmaster1313
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So what keeps the bolt from blowing back on an AR-15?
R.W.Dale
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The locking lugs meshed into the barrel extension
The locking lugs on the bolt.
When a round is chambered, the bolt is locked to the barrel extension and force on the breechface can't unlock it because the bolt lugs have rotated to engage matching lugs on the barrel extension.
The gas pressure routed back to the bolt pushes the bolt carrier back which causes the bolt to rotate and the lugs to disengage from the barrel extension.
The bolt is blown back, but by gas pressure bled from the barrel routed through the gas tube, not by force against the breechface as would occur in a blowback design.
The critical difference is that the breech is locked closed and can't be opened by force against the breechface. In a blowback, the only thing holding the action closed is the inertia of the bolt/slide and the force of the recoil spring.
The gas pressure routed back to the bolt pushes the bolt carrier back which causes the bolt to rotate and the lugs to disengage from the barrel extension.
The bolt is blown back, but by gas pressure bled from the barrel routed through the gas tube, not by force against the breechface as would occur in a blowback design.
The critical difference is that the breech is locked closed and can't be opened by force against the breechface. In a blowback, the only thing holding the action closed is the inertia of the bolt/slide and the force of the recoil spring.
bushmaster1313
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Makes sense.
Nickel Plated
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Well a .223 blowback gun is not necessarily impractical. Look at the HK33 or even the G3 which fires the .308. Those are blowback operated guns.
Granted it's a roller-delayed blowback and not just a straight blowback design like your typical SMG. But blowback none the less. I hear they tend to beat the hell out of your brass because of the pretty violent ejection unlike the softer gas operated designs. But for a military rifle that's hardly important. Not like you have soldiers scouring the field after battle to pick up the brass.
Granted it's a roller-delayed blowback and not just a straight blowback design like your typical SMG. But blowback none the less. I hear they tend to beat the hell out of your brass because of the pretty violent ejection unlike the softer gas operated designs. But for a military rifle that's hardly important. Not like you have soldiers scouring the field after battle to pick up the brass.
The Astra 400 is a blow back design pistol chambered for 9mm Largo. About the same power as 9x19.
The recoil spring is very stiff and it is a bear to manually cycle the slide. If you ever see one, try it and you will understand why only low powered pistols are true blow back designs.
One of the aims of a locked breech design firearm, whether the toggle link M1911 system, rotating bolt like in a AR-15, or the various of other designs, is to reduce the pressure in the barrel to a manageable level before the breech opens.
WardenWolf
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Why not a blowback .223? Because it would require a massive bolt to provide inertia and an extremely heavy spring operating over a long stroke to counter the pressures. You would probably need a winch and pulley to get the action open. That type of action is also high-impact and is absolutely hell on the hardware when scaled above handgun rounds. Metal peens, springs wear out quickly, various parts wind up with reduced lifespans, etc. You name it, all sorts of things go wrong when you try to scale blowback up beyond handgun levels. It's just a Bad Idea and a locking bolt with gas system is the way to go.
Most centerfire handguns are recoil operated rather than blow back. It may seem like splitting hairs, but the main difference is that a recoil operated firearm fires from a locked breech and stays locked until pressures drops. They operate on the rearward force applied to the whole gun (recoil) rather than the rearward force applied to the case (essentially acting as a piston to the bolt).
WardenWolf
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68wj, recoil-operated is just a fancy way of saying "delayed blowback". It's still a blowback, just one with a semi-locking breech to reduce the slide impulse.
mgregg85
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I wonder how strong the action spring would have to be for a blowback .223, that would be a nightmare to cock if someone was ever crazy enough to make one.
boricua9mm
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While the "roleer delayed" part seems like minute detail, it accomplishes the same function; slowing down the opening of the bolt until chamber pressure is at a safe level. No way a straight blowback would be safe in 5.56NATO/.223REM.
The beating of brass seems to be more a function of cycling without any sort of brass deflector. Really, the worst case scenario is the case neck is dented. Many people run a port buffer on HK rifles so that the brass will be in better shape, but also so that it will not go 30 feet away and chip the finish on a rifle valued at $2k+.
You're absolutely right in that retrieving and reloading brass is not a concern in a military pattern rifle like the HK family.
It is entirely feasible to make a blowback 223 but the drawbacks are a huge breechblock, tremendous change in center of gravity as the breech block moves, and a slow rate of fire. Probably some more drawbacks all having to do with a massive breech block slamming into things.
One of the major issues with high pressure blowback mechanisms deal with case friction. If the case is not lubricated it is going to seize in the chamber and gum up the mechanism.
There were a number of highpower delayed blowback mechanism used before WWII and they all used oilers. These were all very messy and the memory of these machine guns is virtually forgotten and due to the Army tin can ammunition coverup of 1921, found in Hatcher's Notebook, you can get into unfortunate debates with people who deign their existence and their function. What replaced oilers was the roller bolt and the fluted chamber. The flutes use gas pressure to float the upper 2/3’rds of the case off the chamber walls. The Mauser Device 06H roller breech was not working until the Germans copied the fluted chamber from a captured Russian machine gun. http://en.wikipedia.org/wiki/StG_45(M) The rest is history.
You can still see lubrication on blow back cartridges, the most common lubricated cartridge is the low pressure 22 LR. Cases are totally coated in a wax and this helps extraction in blowback mechanisms. In cold weather though, the wax will condense and gum up extraction, something I have experienced a number of times in very cold weather.
One of the major issues with high pressure blowback mechanisms deal with case friction. If the case is not lubricated it is going to seize in the chamber and gum up the mechanism.
There were a number of highpower delayed blowback mechanism used before WWII and they all used oilers. These were all very messy and the memory of these machine guns is virtually forgotten and due to the Army tin can ammunition coverup of 1921, found in Hatcher's Notebook, you can get into unfortunate debates with people who deign their existence and their function. What replaced oilers was the roller bolt and the fluted chamber. The flutes use gas pressure to float the upper 2/3’rds of the case off the chamber walls. The Mauser Device 06H roller breech was not working until the Germans copied the fluted chamber from a captured Russian machine gun. http://en.wikipedia.org/wiki/StG_45(M) The rest is history.
You can still see lubrication on blow back cartridges, the most common lubricated cartridge is the low pressure 22 LR. Cases are totally coated in a wax and this helps extraction in blowback mechanisms. In cold weather though, the wax will condense and gum up extraction, something I have experienced a number of times in very cold weather.
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Utilizing recoil force to unlock and cycle the action is not the same as a shell case pushing back into the bolt. They are 2 distinct operating systems. Or maybe blow back is a fancy term for non-locking recoil operation.
Nickel Plated
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if i understand the workings of the HK roller-delayed blowback system correctly, I guess you can say it's a hybrid of a recoil and blowback operated system.
The recoil from the gun moves the bolt-carrier backward, unlocking the rollers. Once the rollers are no longer locking the bolt tot he breech, then the cartridge pushes back the bolt like in a regular blowback gun.
The one advantage of a recoil or blowback operated rifle is that without the gas tube and piston associated with your typical automatic action, you can have an automatic rifle with an actual free-floated barrel. I believe the HK PSG1 rifle is an example of that.
The recoil from the gun moves the bolt-carrier backward, unlocking the rollers. Once the rollers are no longer locking the bolt tot he breech, then the cartridge pushes back the bolt like in a regular blowback gun.
The one advantage of a recoil or blowback operated rifle is that without the gas tube and piston associated with your typical automatic action, you can have an automatic rifle with an actual free-floated barrel. I believe the HK PSG1 rifle is an example of that.
The mechanisms and operation is completely different between blowback and delayed blowback. That's why we differentiate between the two by adding the adjective "delayed" to the latter.
If you think that adding an adjective to a word makes no difference, then I'd be interested to see you post some 25 yard accuracy comparison results for the guns commonly available from Home Depot. Granted, they're caulking guns and staple guns, but guns nonetheless.
Not at all, the HK91 system is a delayed blowback operated weapon. The chamber pressure overcomes the resistance of the locking mechanism in the bolt and drives the bolt assembly out of battery. Enough momentum is imparted to the bolt assembly during the blowback to drive the system through a complete cycle.
After the cartridge primer is struck, the pressure in the chamber rises sharply which pushes the cartridge case back against the face of the bolt. When the force on the bolt is great enough, the locking mechanism releases and the gas pressure accelerates the bolt assembly out of battery. The projectile is out of the barrel by the time the bolt actually unlocks because of the inertia of the bolt assembly and the resistance of the locking mechanism. The bolt assembly reaches a velocity of about 25 feet per second as it is blown out of battery.
pseudonymity
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Erm, kind of. I guess you could say that all systems that do not use gas pressure from a barrel port are blowback, in some sense.
Generally speaking - if the barrel is fixed relative to the frame the action is blowback, if the barrel moves relative to the frame during the action cycle, it is recoil operated.
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