I'm designing a gas delayed blowback operation. Its a pretty rare action that uses the gas to only unlock the bolt. It delays the blowback action until the bullet has left the barrel. I've got most of it already worked out but I've run into one problem. I need to know how close to the muzzle I can put the gas port to delay the action yet still have enough pressure left in it to cycle the blowback action. Or if anyone can find any existing weapons that use this type of operation, that would also be helpful. Thanks.
Gas delayed blowback rifle
- Thread starter Yakov
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Telekinesis
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Check out the HK P7. Its a pistol, not a rifle, but I believe it uses the same type of action you're referring to. Several other HK long arms (G3 and MP5) use roller delayed blow back which might be good designs to look over for some more ideas.
As far as the distance that the port should be from the muzzle, I believe that would take a good bit of mathematical work that depended on the specifics of the rest of your action design, including the type of ammo (and its recoil and pressure characteristics) and your spring rate (a hurdle rate for pressure that the remaining recoil energy would have to overcome to cycle the action).
Also something to consider is that both the G3 and the P7 have fluted chambers to aid in extraction. When these weapons eject casings, it is best described as vigorous. I've seen P7s fling brass over 20' away and throw brass OVER a 10' tall bench covering at a range. I've heard that in early versions the G3 (without fluted chamber) would rip the rims right off the case. And even with the flutes, the G3/PTR 91 is still known for being VERY hard on brass.
Not positive on the exact reason the P7 has a fluted chamber, but I do know that there have been several stress tests where the P7 continued to function reliably (and eject vigerously) WITHOUT an extractor. On that design, the extractor is more about consistency with extraction/ejection angle rather than getting the casing out of the gun.
As far as the distance that the port should be from the muzzle, I believe that would take a good bit of mathematical work that depended on the specifics of the rest of your action design, including the type of ammo (and its recoil and pressure characteristics) and your spring rate (a hurdle rate for pressure that the remaining recoil energy would have to overcome to cycle the action).
Also something to consider is that both the G3 and the P7 have fluted chambers to aid in extraction. When these weapons eject casings, it is best described as vigorous. I've seen P7s fling brass over 20' away and throw brass OVER a 10' tall bench covering at a range. I've heard that in early versions the G3 (without fluted chamber) would rip the rims right off the case. And even with the flutes, the G3/PTR 91 is still known for being VERY hard on brass.
Not positive on the exact reason the P7 has a fluted chamber, but I do know that there have been several stress tests where the P7 continued to function reliably (and eject vigerously) WITHOUT an extractor. On that design, the extractor is more about consistency with extraction/ejection angle rather than getting the casing out of the gun.
benEzra
Moderator Emeritus
Calculations will determine your gas port location. You have two quantities to consider; the pressure starts very high at the chamber end of the barrel and decreases to a fraction of that at the muzzle end, and the duration of the pressure pulse is maximum at the chamber end and near zero at the muzzle.
For optimum operation, you need the right pressure and the right duration. Obviously, delaying the unlocking until the gas pressure has dropped as much as possible (by moving the gas port forward) will ease extraction, BUT at the same time doing so will shorten the duration of the pressure pulse seen by the gas port, making the system less reliable and more ammunition-sensitive.
There is a chart of AR-15 gas port pressures and dwell times by barrel length and port location floating around here on THR somewhere, and I think that chart would be very useful to you.
For optimum operation, you need the right pressure and the right duration. Obviously, delaying the unlocking until the gas pressure has dropped as much as possible (by moving the gas port forward) will ease extraction, BUT at the same time doing so will shorten the duration of the pressure pulse seen by the gas port, making the system less reliable and more ammunition-sensitive.
There is a chart of AR-15 gas port pressures and dwell times by barrel length and port location floating around here on THR somewhere, and I think that chart would be very useful to you.
I need to know how close to the muzzle I can put the gas port to delay the action yet still have enough pressure left in it to cycle the blowback action.
It seems like an engineering problem. Cartridge used, pressures, and mass of reciprocating parts come into play along with a lot of other things. If you don't have the background you can get someone who does or try to read up on it to try and figure it out. Looking how it may be done on another gun really won't be that helpful. You'll need to figure it out using your parameters.
It seems like an engineering problem. Cartridge used, pressures, and mass of reciprocating parts come into play along with a lot of other things. If you don't have the background you can get someone who does or try to read up on it to try and figure it out. Looking how it may be done on another gun really won't be that helpful. You'll need to figure it out using your parameters.
PercyShelley
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One of the problems with talking small arms internals is that there is very little consistency in terminology from source to source. Translating from other languages is an even bigger headache.
Chinn's The Machinegun, which I consider to be the definitive English-language work (there might be better ones in Russian, but I can't read Russian) on automatic firearm mechanisms makes the distinction between delayed blowback and retarded blowback. Most other English-language sources make no such distinction.
To Chinn, a delayed blowback design is one in which the breech is positively locked and unlocks just a little bit afterwards so that the residual chamber pressure can cycle the action. I think this is what the OP is proposing, and it is consistent with Chinn's terminology.
Most English-language sources will describe systems where the breech isn't positively locked, but its movement is slowed down by mechanical ratio, friction or gas pressure as delayed blowback, but Chinn calls these retarded blowback.
Sensu Chinne there are a decent number of retarded blowback small arms designs, but I can think of no delayed blowback small arms. There are a decent number of autocannons that cycle the breech using residual pressure, however. If I had to guess, the short barrel lengths in small arms means that the gas pressure leaves them very quickly, and timing the system to unlock while there is still pressure but not while it is too high is difficult.
Residual chamber pressure is supposed to provide significant, if not primary impetus in cycling the bolt carrier group in some gas-operated small arms. Experiments with gas-operated, rigid roller locked systems in late WWII Germany found excessive BCG velocities that were attributed to residual chamber pressure. I recall reading elsewhere that an M14 has 2KPSI pressure in the cartridge when it unlocks.
Chinn's The Machinegun, which I consider to be the definitive English-language work (there might be better ones in Russian, but I can't read Russian) on automatic firearm mechanisms makes the distinction between delayed blowback and retarded blowback. Most other English-language sources make no such distinction.
To Chinn, a delayed blowback design is one in which the breech is positively locked and unlocks just a little bit afterwards so that the residual chamber pressure can cycle the action. I think this is what the OP is proposing, and it is consistent with Chinn's terminology.
Most English-language sources will describe systems where the breech isn't positively locked, but its movement is slowed down by mechanical ratio, friction or gas pressure as delayed blowback, but Chinn calls these retarded blowback.
Sensu Chinne there are a decent number of retarded blowback small arms designs, but I can think of no delayed blowback small arms. There are a decent number of autocannons that cycle the breech using residual pressure, however. If I had to guess, the short barrel lengths in small arms means that the gas pressure leaves them very quickly, and timing the system to unlock while there is still pressure but not while it is too high is difficult.
Residual chamber pressure is supposed to provide significant, if not primary impetus in cycling the bolt carrier group in some gas-operated small arms. Experiments with gas-operated, rigid roller locked systems in late WWII Germany found excessive BCG velocities that were attributed to residual chamber pressure. I recall reading elsewhere that an M14 has 2KPSI pressure in the cartridge when it unlocks.
PercyShelley
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FWIW here's a chart of the pressure in the barrel of an AR-15 type rifle:
http://www.armalite.com/images/Tech...el Design, Heat, and Reliability, 030824….pdf
As you can see, chamber pressure drops to fairly sane levels very quickly. I suspect that the problem will be in getting the breech mechanism to unlock quickly enough that there is still enough pressure to cycle.
http://www.armalite.com/images/Tech...el Design, Heat, and Reliability, 030824….pdf
As you can see, chamber pressure drops to fairly sane levels very quickly. I suspect that the problem will be in getting the breech mechanism to unlock quickly enough that there is still enough pressure to cycle.
caribou
Member
Look up the layout on the late war Nazi German VG-1, I think was made in the city of Potsdam.
Gas against piston , a true gas delayed blowback, firing an intermediate 8X33Kurtz,( the same cartridge and magazine as the MP/StG-44 series), but made for the Volkssturm on the cheap and quick.
Theres books like "The German Assault Rifle" and "Desperate Measures"(The Collector Series) and others as well as the internet that can get you info, I hope.
Good luck!
Gas against piston , a true gas delayed blowback, firing an intermediate 8X33Kurtz,( the same cartridge and magazine as the MP/StG-44 series), but made for the Volkssturm on the cheap and quick.
Theres books like "The German Assault Rifle" and "Desperate Measures"(The Collector Series) and others as well as the internet that can get you info, I hope.
Good luck!
The VG-1 was a cheap/quick/crude bolt action...what you're thinking of is probably the Gerat 03, 06, and 06H designs. I've got some info on several of them at Forgotten Weapons:
Gerat 06H
Gerat 03 disassembly video
The Gerat 03 used rollers to lock the breech, and a short stroke gas piston to unlock and cycle. The 06H did away with the gas piston, and used just pressure on the rollers to keep the breech closed until pressure has dropped to a safe level (this system went on to be used in the CETME and HK91).
Gerat 06H
Gerat 03 disassembly video
The Gerat 03 used rollers to lock the breech, and a short stroke gas piston to unlock and cycle. The 06H did away with the gas piston, and used just pressure on the rollers to keep the breech closed until pressure has dropped to a safe level (this system went on to be used in the CETME and HK91).
caribou
Member
I was close Ian, its the Volkssturmgewehr 1 - 5 that I was referring to, made by the Gustloff firm. "VG 1 - 5"
Soooooooo, I Googlized my first recollection , and came up with this
http://en.wikipedia.org/wiki/Volkssturmgewehr_1-5
Dang Dash Five, I almost had it ~~LOL!!~~
Soooooooo, I Googlized my first recollection , and came up with this
http://en.wikipedia.org/wiki/Volkssturmgewehr_1-5
Dang Dash Five, I almost had it ~~LOL!!~~
jerkface11
Member
If it's gas delayed blowback then the gas can't be unlocking the bolt. In a gas delayed gun the gas is the only thing holding the bolt closed. There is no locking.
atblis
Member
Steyr GB. Don't know how well it would translate to a rifle cartridge.
JustinJ
Member
"I've got most of it already worked out but I've run into one problem. I need to know how close to the muzzle I can put the gas port to delay the action yet still have enough pressure left in it to cycle the blowback action."
How much pressure is needed to "cycle the blowback action"? No chart is going to tell you that on something you've imagined. One thing to remember in your design is that you must also be able to cycle the action manually.
How much pressure is needed to "cycle the blowback action"? No chart is going to tell you that on something you've imagined. One thing to remember in your design is that you must also be able to cycle the action manually.
caribou
Member
maybe the VG-1-5 is the only gasdelayed rifle I know of...........
what you want to measure is Casehead thrust against the weight of the bolt, the weight of the driving spring and the hammers resistance, if you use a hammer to fire with.
You will want to know the velocity that the bolt travels at as well,both ways, so that you can determine both your bolt stroke and how much time the case takes to extract from the chamber, and how much time you need to keep it closed.
what you want to measure is Casehead thrust against the weight of the bolt, the weight of the driving spring and the hammers resistance, if you use a hammer to fire with.
You will want to know the velocity that the bolt travels at as well,both ways, so that you can determine both your bolt stroke and how much time the case takes to extract from the chamber, and how much time you need to keep it closed.
Yakov,
Don't make the mistake in operation theory that many make and think a Gas Delay Blow Back Action is ever "locked." It's not, the very nature of being a "blow back" design which primarily operates from inertia precludes it from being a locked design as we know it. If you are trying to design a hybrid system then you might have something that would be novel and useful.
The gas is a "retarding" mechanism, just as rollers, links, sliding blocks, etc. are retarding mechanisms on other delayed blow back systems. Not to be confused with short or long "recoil operated" systems which are "locked." The locking refers to the cartridge being locked into the chamber, it has no bearing as to whether or not that chamber may be on a "sled" recoiling at the time. Locking is very important with high pressure cartridges, not so much with small scale or low pressure cartridges. For instance the VG1-5 as well as the H&K roller delay blow back designs use fluted chambers or necks to create a gas film around the cartridge to allow it to move before the pressure has subsided. Without that gas "lubrication" the case would obturate and seize against the walls. The result is usually a ruptured or separated case.
To retard means to diminish or reduce, that's all. The VG1-5 is the only rifle or sub-rifle cartridge that was ever produced using that system. You need to also remember the gun needed the steel cases they had turned to as a alternative material to operate correctly, the brass cases would obturate too much and grab the walls. The current H&K battle rifles have gone to more flute length and the delay roller action actually slows the head down to a crawl while accelerating the rear of the group to keep the inertia necessary to extract the cartridge and cycle the action. There are three pistols that made it to production status including a Chinese design that is rather large and clunky.
I have a PSP, a P7 and a GB. I was once on the quest for an alternative pistol design and have played with them quite a bit. Note these pistols are all 9X19, there is a reason for that. H&K produced a few P7M10s in .40S&W and there was the .45ACP version called the P7M7 (maybe 6 or 7 were produced). There were also some non-gas delay P7 versions in smaller calibers that were pure blow back, but not germane to this discussion. The problem with the larger calibers is that the bullet mass required an increasingly heavier slide. The P7M10 was nicknamed "the whale." Even the GB is big and a bit clunky, that’s primarily because of the large multiple ports, their position and the large “chamber” and “piston” created with the barrel and surrounding chamber. The larger volume doesn’t have enough gas to fill it quickly enough and the ports are further up the barrel. The increased slide size gives you mass that is balance with the gas.
Always remember all of those pistols as well as the VG1-5 have the cases being extracted from the instant the inertia of the system is overcome. The gas is just an aid or an alternative to help you reduce the amount of mass you have to put behind the case. They are still blow back actions, not locked. The 9x19 is a very strong pistol case relative to the bullet size and weight. It can operate in pressure ranges that would rupture other cases. Modern military rifle cartridges operate in the range of 50,000-62,000 psi this includes 5.56x45, 5.45x39, 7.62x39, 7.62x51 or even the 5.7x28 P90 cartridge. The 9X19 even at the highest allowable NATO pressure is at 36,500 psi, the SAAMI +P is 38,500.
Unless you are going to design weapon that will stretch brass a’ la the HK rifles or like a lot of the machine guns that are extracting while under pressure you are going to need to lock the cartridge until the pressure has attenuated enough.
Best of luck to you,
Mako
Don't make the mistake in operation theory that many make and think a Gas Delay Blow Back Action is ever "locked." It's not, the very nature of being a "blow back" design which primarily operates from inertia precludes it from being a locked design as we know it. If you are trying to design a hybrid system then you might have something that would be novel and useful.
The gas is a "retarding" mechanism, just as rollers, links, sliding blocks, etc. are retarding mechanisms on other delayed blow back systems. Not to be confused with short or long "recoil operated" systems which are "locked." The locking refers to the cartridge being locked into the chamber, it has no bearing as to whether or not that chamber may be on a "sled" recoiling at the time. Locking is very important with high pressure cartridges, not so much with small scale or low pressure cartridges. For instance the VG1-5 as well as the H&K roller delay blow back designs use fluted chambers or necks to create a gas film around the cartridge to allow it to move before the pressure has subsided. Without that gas "lubrication" the case would obturate and seize against the walls. The result is usually a ruptured or separated case.
To retard means to diminish or reduce, that's all. The VG1-5 is the only rifle or sub-rifle cartridge that was ever produced using that system. You need to also remember the gun needed the steel cases they had turned to as a alternative material to operate correctly, the brass cases would obturate too much and grab the walls. The current H&K battle rifles have gone to more flute length and the delay roller action actually slows the head down to a crawl while accelerating the rear of the group to keep the inertia necessary to extract the cartridge and cycle the action. There are three pistols that made it to production status including a Chinese design that is rather large and clunky.
I have a PSP, a P7 and a GB. I was once on the quest for an alternative pistol design and have played with them quite a bit. Note these pistols are all 9X19, there is a reason for that. H&K produced a few P7M10s in .40S&W and there was the .45ACP version called the P7M7 (maybe 6 or 7 were produced). There were also some non-gas delay P7 versions in smaller calibers that were pure blow back, but not germane to this discussion. The problem with the larger calibers is that the bullet mass required an increasingly heavier slide. The P7M10 was nicknamed "the whale." Even the GB is big and a bit clunky, that’s primarily because of the large multiple ports, their position and the large “chamber” and “piston” created with the barrel and surrounding chamber. The larger volume doesn’t have enough gas to fill it quickly enough and the ports are further up the barrel. The increased slide size gives you mass that is balance with the gas.
Always remember all of those pistols as well as the VG1-5 have the cases being extracted from the instant the inertia of the system is overcome. The gas is just an aid or an alternative to help you reduce the amount of mass you have to put behind the case. They are still blow back actions, not locked. The 9x19 is a very strong pistol case relative to the bullet size and weight. It can operate in pressure ranges that would rupture other cases. Modern military rifle cartridges operate in the range of 50,000-62,000 psi this includes 5.56x45, 5.45x39, 7.62x39, 7.62x51 or even the 5.7x28 P90 cartridge. The 9X19 even at the highest allowable NATO pressure is at 36,500 psi, the SAAMI +P is 38,500.
Unless you are going to design weapon that will stretch brass a’ la the HK rifles or like a lot of the machine guns that are extracting while under pressure you are going to need to lock the cartridge until the pressure has attenuated enough.
Best of luck to you,
Mako
caribou
Member
do not scrap ideas, compare and improve,try and fail or suceed, then improve. weapons eveolve through several prototyps, they rarely get it right the first time, takes years, even for the best......... never give up........learn all you can and play with paper and pencil, you never know unless you try.......
Yakov,
Don't abandon it, refine it.
Just remember though, once the bullet has left the barrel you've lost most of your pressure and unless the bolt is already moving it won't just start moving unless it has a force applied to it. If you look at gas operated, recoil operated or even delay blowback systems such as roller delay systems something is in motion before the bullet leave the barrel and the pressure drops. In the case of gas guns an operating rod or a bolt carrier or something is in motion waiting to cam and unlock the bolt. In the case of the recoil operated systems the breech is locked but it is moving back still locked to the barrel. I the case of the gas delay roller the forward section of the bolt has move a small amount bu the rear section has been accelerated at a rate that will unlock the action after the bullet is either gone or sufficiently up the barrel that the bullet is out.
With a blow back system the bolt is always moving, it's just a matter of how fast or what the pressure is and can the case contain it without being fully supported by the chamber.
Get creative...
~Mako
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