Idea for a gas operation

Cutaway · February 9, 2015, 08:55 PM

An existing rotating bolt but with exactly 1mm of the rear of the locking lugs filed off. This allows gas to flood the chamber past the locking lugs to the bolt carrier with a head that acts as a gas piston. This would save drilling holes in the barrel to install gas pistons and make gas operation simple and near to that of blowback operation.

It may or may not have the 1mm headspace as previously mentioned but angled lugs to ease extraction and reloading. It may also have a self cleaning bolt to remove residue inside the receiver and a fluted chamber.

To explain again, When firing, the bolt is in a fully locked position, the fully locked bolt moves backwards 1mm allowing the gas pressure to flood the chamber past the locking lugs. The gas pressure has to overcome the bolt carrier to unlock the bolt and reload.

Just to notify, this operation may vary (IE: rear locking lugs, internal locking piston, locking flaps etc)

Gunplummer · February 10, 2015, 02:02 AM

Maybe with steel cased ammo. I have examined a lot of rifles that had the wrong cartridge loaded in them, and most had the gas sealed by the brass. I had one where the under length case stretched about .200 and sealed the chamber. I have seen the tanker model M-240's with the rate turned too high and flames coming out of the chamber with extraction. Does not sound practical to me, but you never know until you try it.

**Unclenick** · February 10, 2015, 08:28 AM

As mentioned, cases expand to seal the chamber, so the pressurized gas path you depicted does not exist. Keeping gas out of the shooter's face is part of the case function. In high power rifle they expand so firmly that cases actually stick to the chamber walls by friction, which is why the heads stretch to the rear and thin the case just in front of the head (the pressure ring) rather than the whole case backing up, as it does in all but the highest pressure handgun cartridges. You would have to at least flute the chamber to get gas to the rear of the gun.

Second, full pressure, as opposed to trickled out pressure, will gas cut even steel. Take a look at the bolt faces of much-fired military rifles and you see pitting all around the firing pin tunnel where tiny leaks around the sides of the primers have actually cut enough steel to give it a severe case a acne. So you have to reduce the pressure to use is for mechanical operation. This is what the constriction of gas ports in a barrel do. That, and they are located far enough from the chamber that they aren't exposed to gas cutting by the full peak chamber pressure.

Third, if you start opening the gun while the pressure is still high, the cases will blow out at the pressure ring, separating the head. That leaves most of the case stuck in the chamber, preventing the next round from chambering. If this happens with the bolt open far enough, it will release enough gas to ruin the gun same as an out-of-battery firing event. These generally blow the perimeter of the bolt face off by gas cutting and blow the bottom out of the magazine and ammunition there gets flattened and the stock is splintered. To prevent over-rapid extraction of a case still under significant pressure, most self-loading mechanisms that don't use massive bolts have to include a delayed opening mechanism to avoid this. There are a number of mechanisms to accomplish delayed opening.

I suggest getting a copy of Hatcher's Notebook and reading about various mechanisms that delay opening. The Wikipedia entry on blow-back operated guns has a long list of delay mechanisms you can study.

Finally, if you do come up with a novel mechanism that is workable and practical economically, and you publish it as a drawing, under the new First-To-File rules, someone may steel it and file for a patent on it. I have 11 issued patents, but they were all issued under the old First To Invent system that change three years ago. The new rules were made to convenience big companies filing lots of patents, but as near as I can discern, are no friend of the individual inventor. Once you put it out there, you now risk losing it, where the old system gave you a year to file after publishing an idea somewhere.

Scorch · February 10, 2015, 11:35 AM

It works, and has for several decades. HK rifles use fluted chambers to "float" the case on a bed of hot gas to assist with extraction. Only problem you run into is that the gas deposits carbon as it cools, thus rendering your operating system unworkable.

Gunplummer · February 10, 2015, 02:09 PM

Never worked on one, but that sounds a little weird. I remember seeing pounds of plastic cased training empties laying around the range. The WWII Russian semi-auto had a fluted chamber for ease of extraction also, but it involved less contact on the case, not as an assist to bolt movement. Now I guess I have to buy an H&K.

Dixie Gunsmithing · February 10, 2015, 08:06 PM

Winchester had a patent years ago, for a similar process of fluting the chamber in shotgun barrels. It was supposed to help with the extraction of paper shotshells. I think it came out about the same time as the model 12 patents. The old paper shotshell sleeves would swell up when damp, so they had feeding issues. I don't think it ever went into production, that I know of.

gunnut69 · February 11, 2015, 02:06 AM

The HK fluted chambers purpose is to ease extraction as a large portion of the cases sealing surface is negated. The HK's operating system is a gas controlled blowback and very violent. Without the fluting case heads are torn off. The action delays opening using rollers held in lock by gas pressure. Its a very violent operating system.

Gunplummer · February 11, 2015, 02:11 AM

That sounds more like it. The brass looks pretty dinged up that is laying around one on the range.

BoogieMan · February 11, 2015, 07:33 AM

I think you may need to think smaller. Maybe an improvement upon a existing design before moving to revolutionize semi auto guns.
There is a reason that blowback and gas operated designs havent been combined in the past.
You may want to look into some rotating bolt blowback systems such as the Frommer to give you inspiration.

Dixie Gunsmithing · February 11, 2015, 09:29 AM

They've took pain blowback to 9mm, but really, 9mm ought to be in a locked breech, or I always thought. The four unlocked bolt rounds you'll see the most are the .22 LR, the .25 Auto, the .380 Auto, and the 9mm Auto.

It is according to the barrel length, and how fast the bullet will leave the muzzle, before any high pressure gas can escape reward from the breech. In a 9mm, then, the shorter the barrel and heavier the slide or bolt, the better, if it's non-locked. We know there is some gas escape from the non-locked, by evidence of the soot. That soot is an indication that the chamber could be burnt and enlarged, or egg-shaped, the longer it is shot.

BigG · February 11, 2015, 09:39 AM

Dixiegunsmithing: Think you mean 32 Auto or 7.65 Auto instead of 9mm auto.

Dixie Gunsmithing · February 11, 2015, 10:19 AM

No, they have done the 9mm as blow-back too. I did forget the .32 auto, etc.

**Unclenick** · February 11, 2015, 11:18 AM

45 Auto grease guns were blow-back, too, though they ran from an open bolt. Some 20 mm guns are blow-back, too, though they use primer ignition advance to allow the bolt mass to be cut in half. I think the Hi-Point pistols are all blow-back including the 9 mm, 40 S&W and 45 Auto pistol. Despite having a polymer frame, the latter two weigh 2¼ lbs. That weight must be mostly in the slide, which looks just massive in pictures of them.

**4V50 Gary** · February 11, 2015, 11:26 AM

Agree with Sorch. It sounds like the fluted chamber needs to be incorporated into the design for the gases to flow back. There's got to be some sort of dwell (delay) before the bolt is allowed to unlock and the extraction process begun.

**Unclenick** · February 11, 2015, 11:40 AM

And the flutes will bleed pressure back, so it won't be full peak pressure presented suddenly. That's why I suggested fluting was the least he needed to do. When you pick up cases that have been fired in a fluted chamber and examine them, the strongest flute impressions are at the mouth. They fade as you go down from the neck. This is partly due to the brass thickening further down, and partly due to the pressure gradient dropping pressure as it comes away from the neck.

James K · February 11, 2015, 12:48 PM

IIRC, the most powerful blowbacks were the Astra 600/400/800. But they have heavy slides, powerful recoil springs and a little trick in making the hammer at a mechanical disadvantage so it acts as a delaying mechanism (The 800 (Condor) doesn't have that and had problems when they tried it with the 9mm Largo, though it worked OK with 9mm Parabellum.)

The HK system was roller locked. But its operation depends on allowing the base of the case to move backward a couple of millimeters; that was enough to tear off the case head unless the whole case was allowed to move back. That could only be done by keeping the case walls from gripping the chamber wall, hence the fluted chamber.

What the OP seems to be reaching for is something of the same idea, allowing the case to move back and act as a short stroke piston (like the "new" Remington R51 if they ever get it working right).

But that is tricky with high pressure rifle cartridges. I think it is back to the drawing board on this one.

Jim

Gunfixr · February 11, 2015, 01:36 PM

The case is supposed to seal the chamber upon firing. If not, full chamber pressure will blast back into the action, and you do not want to be anywhere near this. Even steel cases swell enough to seal in the vast majority of the gases in.
All self repeating actions are delayed, and must be. If the action were to start opening before the bullet leaves the barrel, chamber pressure is going to blow the case head out the back. You are talking about 1000s of lbs of pressure per square inch. Think of a tire exploding, times 1000, with your hand or face right next to it.
The hk flutes are shallower at the case mouth so that the case can seal. Also, they are very shallow, so the case doesn't just fill them up.
In order for the gas to go straight to the bolt and push, the bolt would have to seal the chamber, and stay that way with wear. This has been tried, and it failed. Blowback is still not immediate, the weight and spring strength delay the opening until the bullet has left the bore, and pressure drops. Residual pressure and momentum is what operates the system. In a gas system, the delay is caused by location of the port, and parts movement required to operate the action.
While a neat theory, trying to float the case in a layer of gas that directly operates the bolt will not work for several reasons. If it did, someone would be making it. The simplest action is still blowback, followed by recoil operated locked breech.

Cutaway · February 11, 2015, 02:50 PM

Thats the point of the operation, to use gas pressure from the fluted chamber to overcome the bolt carrier to unlock and reload. It would make it simple as blowback operation. I dont think the cartridges would rupture much but when extracting would be hot.

Regarding the 1mm headspace and filed lugs, this was just the first idea. It would be better off using the fluted chamber.

It may also vary using various locking operations, the likes of rear locking lugs, internal piston, locking flaps as it may be more resistant to dirt.

Dixie Gunsmithing · February 11, 2015, 03:08 PM

You might look at something similar to the Winchester model 50 short stroke floating chamber action. However, the problem is keeping it clean. One could keep the barrel and bolt locked together for just part of a recoil stroke, and have it release maybe 1/4 the way back, where the bolt would keep going rearward, and the barrel or chamber would reset forward. One might even look at incorporating a pistol locking scheme into a rifle here.

The main problem you'll have is carbon soot fouling up the works, by allowing gas by the fired round.

skizzums · February 11, 2015, 03:19 PM

I wonder if you could do this with a primerless case and electronic ignition. still, would be incredibly dirty. I am thinking a piece of thin metal like foil on the back of the bullet, with no flash-hole, electronic ignition and the pressure can blast out of the back of the bullet. but even though that is quite unrealistic, besides the amazing blow-back, I imagine the bullet would also never get up to it's full velocity no matter how you sliced it.

Dixie Gunsmithing · February 11, 2015, 08:37 PM

Unclenick,

I forgot about the M3 Grease Gun in .45 ACP. It did have a heavy bolt in it. Also, there was the Sten, which was 9mm and blowback. I guess it was the British version of the M3. Of course it had side mounted magazine that did give some problems. There's the Sterling too. The next I can think of is the MAC-10 and the Uzi. All these fired with direct blowback and from an open bolt, which was made heavy enough to counter some of the opening speed of the bolt.

I've read a lot about the Thompson 1921A firing okay with the wedge (lock) removed, so one could almost count it in as another .45 ACP. Though I think it was hard on the buffer when doing it.

Gunplummer · February 12, 2015, 01:55 PM

I had an original MAC-11 (Open bolt) and the bolt was not all that heavy but the springs were. This gun fired as the bolt was still closing and the momentum of the bolt going forward helped slow the blowback operation.

Dixie Gunsmithing · February 12, 2015, 03:28 PM

Open bolts are different critters, in that the bolts have a forward momentum or inertia, that has to be overcome before reversing direction. Some have an extended recoil distance too. I don't think the time delay is very much at all, though it's there.

A variant, in a way, is the newer inertia bolts in the Benelli's, where the bolt is two piece, which are held apart by a spring. During recoil, the rear of the bolt is trying to stay stationary, as the gun recoils, and actually twists the front of the bolt toward locking, compressing the spring, before its overcome with recoil energy, where the spring expands, unlocks, and all travels rearward.

The Hi-Point pistols just rely on plain recoil, as they use the same frame between the .380 and the 9mm. Both have a fixed barrel.

James K · February 12, 2015, 10:27 PM

Just FWIW, the M1921/28 Thompson can't be fired with the Blish lock removed since the lock connects the bolt to the bolt handle and without the lock the gun can't be cocked. (I have heard of jury rigged "fixes", but they seem to be "war stories" rather than actual happenings.) The M1 and M1A1 Thompson have no lock, but the bolt is heavier and the rear of the receiver was made heavier because it kept breaking out.

I realize that in my earlier post I was thinking of blowback handguns, not long guns or SMG's.

In looking at the OP's drawing again, I think the real problem would be that the gas would move back alongside the case (through flutes) so fast that the pressure would not have time to drop. In that case, the flutes would not help; the bolt would open, the case head would blow out and the gun would be wrecked.

The only way, IMHO, to make a system like that work would be use the bolt head as a short stroke piston and to build a very long dwell time into that cam. My general feeling is that there is a lot of difference between drawing neat pictures with a CAD program and actually getting something to work when dealing with thousands of PSI and high speed gas movement.

Jim

Dixie Gunsmithing · February 13, 2015, 08:29 AM

Jim,

They actually did try it with the 1921, but it was modified by using some sort of replacement handle for the lock. The problem they found was beating the buffer to pieces, even with a stouter recoil spring, and mis-fired rounds over the so-called hammer's action. I think this is what lead to them figuring out the newer M1. They did as you said, and ended up using a fixed firing pin, and removing the hammer. I can't recall what the problem with the hammer actually was, (breakage, etc), but a fixed firing pin for the open bolt was what was needed.

The ones who claimed a successful conversion of the 1921, though, are something else.

February 9, 2015, 08:55 PM	#1
Cutaway Member Join Date: October 9, 2008 Posts: 23	Idea for a gas operation An existing rotating bolt but with exactly 1mm of the rear of the locking lugs filed off. This allows gas to flood the chamber past the locking lugs to the bolt carrier with a head that acts as a gas piston. This would save drilling holes in the barrel to install gas pistons and make gas operation simple and near to that of blowback operation. It may or may not have the 1mm headspace as previously mentioned but angled lugs to ease extraction and reloading. It may also have a self cleaning bolt to remove residue inside the receiver and a fluted chamber. To explain again, When firing, the bolt is in a fully locked position, the fully locked bolt moves backwards 1mm allowing the gas pressure to flood the chamber past the locking lugs. The gas pressure has to overcome the bolt carrier to unlock the bolt and reload. Just to notify, this operation may vary (IE: rear locking lugs, internal locking piston, locking flaps etc) __________________ DILLIGAF KB Wilson. Neca eos omnes. Deus suos agnoset. (Not KB Wilson).

February 10, 2015, 08:28 AM	#3
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,061	Several problems As mentioned, cases expand to seal the chamber, so the pressurized gas path you depicted does not exist. Keeping gas out of the shooter's face is part of the case function. In high power rifle they expand so firmly that cases actually stick to the chamber walls by friction, which is why the heads stretch to the rear and thin the case just in front of the head (the pressure ring) rather than the whole case backing up, as it does in all but the highest pressure handgun cartridges. You would have to at least flute the chamber to get gas to the rear of the gun. Second, full pressure, as opposed to trickled out pressure, will gas cut even steel. Take a look at the bolt faces of much-fired military rifles and you see pitting all around the firing pin tunnel where tiny leaks around the sides of the primers have actually cut enough steel to give it a severe case a acne. So you have to reduce the pressure to use is for mechanical operation. This is what the constriction of gas ports in a barrel do. That, and they are located far enough from the chamber that they aren't exposed to gas cutting by the full peak chamber pressure. Third, if you start opening the gun while the pressure is still high, the cases will blow out at the pressure ring, separating the head. That leaves most of the case stuck in the chamber, preventing the next round from chambering. If this happens with the bolt open far enough, it will release enough gas to ruin the gun same as an out-of-battery firing event. These generally blow the perimeter of the bolt face off by gas cutting and blow the bottom out of the magazine and ammunition there gets flattened and the stock is splintered. To prevent over-rapid extraction of a case still under significant pressure, most self-loading mechanisms that don't use massive bolts have to include a delayed opening mechanism to avoid this. There are a number of mechanisms to accomplish delayed opening. I suggest getting a copy of Hatcher's Notebook and reading about various mechanisms that delay opening. The Wikipedia entry on blow-back operated guns has a long list of delay mechanisms you can study. Finally, if you do come up with a novel mechanism that is workable and practical economically, and you publish it as a drawing, under the new First-To-File rules, someone may steel it and file for a patent on it. I have 11 issued patents, but they were all issued under the old First To Invent system that change three years ago. The new rules were made to convenience big companies filing lots of patents, but as near as I can discern, are no friend of the individual inventor. Once you put it out there, you now risk losing it, where the old system gave you a year to file after publishing an idea somewhere. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

February 10, 2015, 11:35 AM	#4
Scorch Senior Member Join Date: February 13, 2006 Location: Washington state Posts: 15,248	It works, and has for several decades. HK rifles use fluted chambers to "float" the case on a bed of hot gas to assist with extraction. Only problem you run into is that the gas deposits carbon as it cools, thus rendering your operating system unworkable. __________________ Never try to educate someone who resists knowledge at all costs. But what do I know? Summit Arms Services

February 11, 2015, 07:33 AM	#9
BoogieMan Senior Member Join Date: April 4, 2012 Location: South Jersey Posts: 2,217	I think you may need to think smaller. Maybe an improvement upon a existing design before moving to revolutionize semi auto guns. There is a reason that blowback and gas operated designs havent been combined in the past. You may want to look into some rotating bolt blowback systems such as the Frommer to give you inspiration. __________________ Concentrated power is not rendered harmless by the good intentions of those who create it. Milton Freidman "If you find yourself in a fair fight,,, Your tactics suck"- Unknown

February 11, 2015, 09:39 AM	#11
BigG Senior Member Join Date: May 19, 1999 Location: Atlanta, GA Posts: 4,334	Dixiegunsmithing: Think you mean 32 Auto or 7.65 Auto instead of 9mm auto. __________________ o "The Earth is degenerating today. Bribery and corruption abound. Children no longer obey their parents, every man wants to write a book, and it is evident that the end of the world is fast approaching." Assyrian tablet, c. 2800 BC o "In the beginning of a change, the patriot is a scarce man brave, hated, and scorned. When his cause succeeds, however, the timid join him, for then it costs nothing to be a patriot." Mark Twain o "They have gun control in Cuba. They have universal health care in Cuba. So why do they want to come here?" Paul Harvey o TODAY WE CARVE OUT OUR OWN OMENS! Leonidas, Thermopylae, 480 BC

February 10, 2015, 02:02 AM	#2
Gunplummer Senior Member Join Date: March 11, 2010 Location: South East Pa. Posts: 3,364	Maybe with steel cased ammo. I have examined a lot of rifles that had the wrong cartridge loaded in them, and most had the gas sealed by the brass. I had one where the under length case stretched about .200 and sealed the chamber. I have seen the tanker model M-240's with the rate turned too high and flames coming out of the chamber with extraction. Does not sound practical to me, but you never know until you try it.

February 10, 2015, 02:09 PM	#5
Gunplummer Senior Member Join Date: March 11, 2010 Location: South East Pa. Posts: 3,364	Never worked on one, but that sounds a little weird. I remember seeing pounds of plastic cased training empties laying around the range. The WWII Russian semi-auto had a fluted chamber for ease of extraction also, but it involved less contact on the case, not as an assist to bolt movement. Now I guess I have to buy an H&K.

February 10, 2015, 08:06 PM	#6
Dixie Gunsmithing Moderator Emeritus Join Date: April 27, 2013 Location: Ohio Posts: 1,923	Winchester had a patent years ago, for a similar process of fluting the chamber in shotgun barrels. It was supposed to help with the extraction of paper shotshells. I think it came out about the same time as the model 12 patents. The old paper shotshell sleeves would swell up when damp, so they had feeding issues. I don't think it ever went into production, that I know of.

February 11, 2015, 02:06 AM	#7
gunnut69 Member Join Date: June 23, 2013 Posts: 40	The HK fluted chambers purpose is to ease extraction as a large portion of the cases sealing surface is negated. The HK's operating system is a gas controlled blowback and very violent. Without the fluting case heads are torn off. The action delays opening using rollers held in lock by gas pressure. Its a very violent operating system.

February 11, 2015, 02:11 AM	#8
Gunplummer Senior Member Join Date: March 11, 2010 Location: South East Pa. Posts: 3,364	That sounds more like it. The brass looks pretty dinged up that is laying around one on the range.

February 11, 2015, 09:29 AM	#10
Dixie Gunsmithing Moderator Emeritus Join Date: April 27, 2013 Location: Ohio Posts: 1,923	They've took pain blowback to 9mm, but really, 9mm ought to be in a locked breech, or I always thought. The four unlocked bolt rounds you'll see the most are the .22 LR, the .25 Auto, the .380 Auto, and the 9mm Auto. It is according to the barrel length, and how fast the bullet will leave the muzzle, before any high pressure gas can escape reward from the breech. In a 9mm, then, the shorter the barrel and heavier the slide or bolt, the better, if it's non-locked. We know there is some gas escape from the non-locked, by evidence of the soot. That soot is an indication that the chamber could be burnt and enlarged, or egg-shaped, the longer it is shot.

February 11, 2015, 10:19 AM	#12
Dixie Gunsmithing Moderator Emeritus Join Date: April 27, 2013 Location: Ohio Posts: 1,923	No, they have done the 9mm as blow-back too. I did forget the .32 auto, etc.

February 11, 2015, 11:18 AM	#13
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,061	45 Auto grease guns were blow-back, too, though they ran from an open bolt. Some 20 mm guns are blow-back, too, though they use primer ignition advance to allow the bolt mass to be cut in half. I think the Hi-Point pistols are all blow-back including the 9 mm, 40 S&W and 45 Auto pistol. Despite having a polymer frame, the latter two weigh 2¼ lbs. That weight must be mostly in the slide, which looks just massive in pictures of them. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

February 11, 2015, 11:26 AM	#14
4V50 Gary Staff Join Date: November 2, 1998 Location: Colorado Posts: 21,832	Agree with Sorch. It sounds like the fluted chamber needs to be incorporated into the design for the gases to flow back. There's got to be some sort of dwell (delay) before the bolt is allowed to unlock and the extraction process begun. __________________ Vigilantibus et non dormientibus jura subveniunt. *Molon Labe!*

February 11, 2015, 11:40 AM	#15
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,061	And the flutes will bleed pressure back, so it won't be full peak pressure presented suddenly. That's why I suggested fluting was the least he needed to do. When you pick up cases that have been fired in a fluted chamber and examine them, the strongest flute impressions are at the mouth. They fade as you go down from the neck. This is partly due to the brass thickening further down, and partly due to the pressure gradient dropping pressure as it comes away from the neck. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

February 11, 2015, 12:48 PM	#16
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	IIRC, the most powerful blowbacks were the Astra 600/400/800. But they have heavy slides, powerful recoil springs and a little trick in making the hammer at a mechanical disadvantage so it acts as a delaying mechanism (The 800 (Condor) doesn't have that and had problems when they tried it with the 9mm Largo, though it worked OK with 9mm Parabellum.) The HK system was roller locked. But its operation depends on allowing the base of the case to move backward a couple of millimeters; that was enough to tear off the case head unless the whole case was allowed to move back. That could only be done by keeping the case walls from gripping the chamber wall, hence the fluted chamber. What the OP seems to be reaching for is something of the same idea, allowing the case to move back and act as a short stroke piston (like the "new" Remington R51 if they ever get it working right). But that is tricky with high pressure rifle cartridges. I think it is back to the drawing board on this one. Jim

February 11, 2015, 01:36 PM	#17
Gunfixr Senior Member Join Date: June 10, 2007 Location: East Coast, USA Posts: 360	The case is supposed to seal the chamber upon firing. If not, full chamber pressure will blast back into the action, and you do not want to be anywhere near this. Even steel cases swell enough to seal in the vast majority of the gases in. All self repeating actions are delayed, and must be. If the action were to start opening before the bullet leaves the barrel, chamber pressure is going to blow the case head out the back. You are talking about 1000s of lbs of pressure per square inch. Think of a tire exploding, times 1000, with your hand or face right next to it. The hk flutes are shallower at the case mouth so that the case can seal. Also, they are very shallow, so the case doesn't just fill them up. In order for the gas to go straight to the bolt and push, the bolt would have to seal the chamber, and stay that way with wear. This has been tried, and it failed. Blowback is still not immediate, the weight and spring strength delay the opening until the bullet has left the bore, and pressure drops. Residual pressure and momentum is what operates the system. In a gas system, the delay is caused by location of the port, and parts movement required to operate the action. While a neat theory, trying to float the case in a layer of gas that directly operates the bolt will not work for several reasons. If it did, someone would be making it. The simplest action is still blowback, followed by recoil operated locked breech.

February 11, 2015, 02:50 PM	#18
Cutaway Member Join Date: October 9, 2008 Posts: 23	Thats the point of the operation, to use gas pressure from the fluted chamber to overcome the bolt carrier to unlock and reload. It would make it simple as blowback operation. I dont think the cartridges would rupture much but when extracting would be hot. Regarding the 1mm headspace and filed lugs, this was just the first idea. It would be better off using the fluted chamber. It may also vary using various locking operations, the likes of rear locking lugs, internal piston, locking flaps as it may be more resistant to dirt. __________________ DILLIGAF KB Wilson. Neca eos omnes. Deus suos agnoset. (Not KB Wilson).

February 11, 2015, 03:08 PM	#19
Dixie Gunsmithing Moderator Emeritus Join Date: April 27, 2013 Location: Ohio Posts: 1,923	You might look at something similar to the Winchester model 50 short stroke floating chamber action. However, the problem is keeping it clean. One could keep the barrel and bolt locked together for just part of a recoil stroke, and have it release maybe 1/4 the way back, where the bolt would keep going rearward, and the barrel or chamber would reset forward. One might even look at incorporating a pistol locking scheme into a rifle here. The main problem you'll have is carbon soot fouling up the works, by allowing gas by the fired round.

February 11, 2015, 03:19 PM	#20
skizzums Senior Member Join Date: July 1, 2013 Location: Douglasville, Ga Posts: 4,615	I wonder if you could do this with a primerless case and electronic ignition. still, would be incredibly dirty. I am thinking a piece of thin metal like foil on the back of the bullet, with no flash-hole, electronic ignition and the pressure can blast out of the back of the bullet. but even though that is quite unrealistic, besides the amazing blow-back, I imagine the bullet would also never get up to it's full velocity no matter how you sliced it. __________________ My head is bloody, but unbowed

February 11, 2015, 08:37 PM	#21
Dixie Gunsmithing Moderator Emeritus Join Date: April 27, 2013 Location: Ohio Posts: 1,923	Unclenick, I forgot about the M3 Grease Gun in .45 ACP. It did have a heavy bolt in it. Also, there was the Sten, which was 9mm and blowback. I guess it was the British version of the M3. Of course it had side mounted magazine that did give some problems. There's the Sterling too. The next I can think of is the MAC-10 and the Uzi. All these fired with direct blowback and from an open bolt, which was made heavy enough to counter some of the opening speed of the bolt. I've read a lot about the Thompson 1921A firing okay with the wedge (lock) removed, so one could almost count it in as another .45 ACP. Though I think it was hard on the buffer when doing it.

February 12, 2015, 01:55 PM	#22
Gunplummer Senior Member Join Date: March 11, 2010 Location: South East Pa. Posts: 3,364	I had an original MAC-11 (Open bolt) and the bolt was not all that heavy but the springs were. This gun fired as the bolt was still closing and the momentum of the bolt going forward helped slow the blowback operation.

February 12, 2015, 03:28 PM	#23
Dixie Gunsmithing Moderator Emeritus Join Date: April 27, 2013 Location: Ohio Posts: 1,923	Open bolts are different critters, in that the bolts have a forward momentum or inertia, that has to be overcome before reversing direction. Some have an extended recoil distance too. I don't think the time delay is very much at all, though it's there. A variant, in a way, is the newer inertia bolts in the Benelli's, where the bolt is two piece, which are held apart by a spring. During recoil, the rear of the bolt is trying to stay stationary, as the gun recoils, and actually twists the front of the bolt toward locking, compressing the spring, before its overcome with recoil energy, where the spring expands, unlocks, and all travels rearward. The Hi-Point pistols just rely on plain recoil, as they use the same frame between the .380 and the 9mm. Both have a fixed barrel.

February 12, 2015, 10:27 PM	#24
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	Just FWIW, the M1921/28 Thompson can't be fired with the Blish lock removed since the lock connects the bolt to the bolt handle and without the lock the gun can't be cocked. (I have heard of jury rigged "fixes", but they seem to be "war stories" rather than actual happenings.) The M1 and M1A1 Thompson have no lock, but the bolt is heavier and the rear of the receiver was made heavier because it kept breaking out. I realize that in my earlier post I was thinking of blowback handguns, not long guns or SMG's. In looking at the OP's drawing again, I think the real problem would be that the gas would move back alongside the case (through flutes) so fast that the pressure would not have time to drop. In that case, the flutes would not help; the bolt would open, the case head would blow out and the gun would be wrecked. The only way, IMHO, to make a system like that work would be use the bolt head as a short stroke piston and to build a very long dwell time into that cam. My general feeling is that there is a lot of difference between drawing neat pictures with a CAD program and actually getting something to work when dealing with thousands of PSI and high speed gas movement. Jim

February 13, 2015, 08:29 AM	#25
Dixie Gunsmithing Moderator Emeritus Join Date: April 27, 2013 Location: Ohio Posts: 1,923	Jim, They actually did try it with the 1921, but it was modified by using some sort of replacement handle for the lock. The problem they found was beating the buffer to pieces, even with a stouter recoil spring, and mis-fired rounds over the so-called hammer's action. I think this is what lead to them figuring out the newer M1. They did as you said, and ended up using a fixed firing pin, and removing the hammer. I can't recall what the problem with the hammer actually was, (breakage, etc), but a fixed firing pin for the open bolt was what was needed. The ones who claimed a successful conversion of the 1921, though, are something else.