toggle link action strength

[Slamfire]

The Oerlikon 20mm/70 was a straight blow-back, there is no delay....

The Oerlikon and the MK-108 were straight blow-back designs. There is no delay between firing and the movement of the breech face. They did use rebated rims so the bolt could follow the base of the round inside the chamber and used a very long headspace to support the case longer, but that is not a delayed blow-back

A delayed blow-back design delays the motion of the breech face by mechanical disadvantage, as shown:

It is a matter of classification, but I thought the advanced primer ignition actions were classified as delayed blowbacks.

Toggles can be extremely stable, go over top dead center with a buttress on the links to prevent over-rotation, they aren't unlocking, no matter the load. If you look at any toggle lock design the toggle rotates to just over dead center and then stops, careful examination will reveal that they are actually .5 to 1 degree over center. The toggle will not break until the joint is rotated a degree or two.

Can you provide a link so I can have an idea of what you meant by buttress on the links?. I googled that and got flying buttresses.

I don't know if a degree or two is a tight tolerance or not for a fire arms mechanism. Intuitively it seems tight. You are right they have been used in a number of semi automatic and automatic mechanisms, and I assumed it was because it was easy to knock them out of alignment and get the toggle to break.

 

[barnbwt]

Toggles can be extremely stable, go over top dead center with a buttress on the links to prevent over-rotation, they aren't unlocking, no matter the load.

By going over center, the breech face sets back a hair, same as when the series of linkages flex and squish as they are loaded. The ultimate load capacity can be as strong as any other action, but for a given mass of load-bearing elements, the breechface will always move more than a system that directly locks a bolt into a receiver recess (and/or barrel extension) as close to the chamber as possible.

TCB

 

[lysanderxiii]

By going over center, the breech face sets back a hair, same as when the series of linkages flex and squish as they are loaded. The ultimate load capacity can be as strong as any other action, but for a given mass of load-bearing elements, the breechface will always move more than a system that directly locks a bolt into a receiver recess (and/or barrel extension) as close to the chamber as possible.

TCB

True, the number of joints has a large influence on the flexibility (as does the distance between the breech face and actual locking surfaces), but not necessarily its strength.

The Maxim, with its toggle lock was quite successful in the 2 pounder version....

 

[lysanderxiii]

It is a matter of classification, but I thought the advanced primer ignition actions were classified as delayed blowbacks.

No, delayed blow-backs are any unlocked mechanism that uses a mechanical disadvantage to delay the movement of the breech face during the high pressure phase of the firing.

Advanced ignition, is just hitting the primer before the bolt comes to a complete stop, it can't be used in locked or delayed systems as all the delaying, or locking parts wouldn't be in place, or you would have a large set back, basically and very long chamber headspace.

Strictly speaking, the M1 Thompson, STEN, M3, and any other blow-back with a firing pin machined onto the face of the breech has a small degree of advanced ignition. The bolt has to be moving forward, and the case has to be stopped in order for the 'firing pin' to dent the primer....

The whole intent of advanced ignition is to use the forward momentum of the bolt to resist the rearward thrust of the cartridge going off. The chamber pressure first has to stop the forward motion of the bolt, then start to accelerate it to the rear, allows a lighter bolt for the same power cartridge, or a more powerful cartridge with the same weight bolt.

It has been successfully used to make simple blow-backs as big as 83 mm....

Can you provide a link so I can have an idea of what you meant by buttress on the links?. I googled that and got flying buttresses.

I don't know if a degree or two is a tight tolerance or not for a fire arms mechanism. Intuitively it seems tight. You are right they have been used in a number of semi automatic and automatic mechanisms, and I assumed it was because it was easy to knock them out of alignment and get the toggle to break.

Buttress - (n) a projecting support.

The buttresses are the supports that prevent rotation beyond that desired.



A degree is sufficient as the a vast majority of the force on the toggle is taken by the two projecting faces.

The main reason it isn't used that much today is 1) more parts, 2) loaded pins, so they need to be close toleranced, 3) needs room for the toggle to fold, or unfold, and 4) it is more flexible, and over many loading cycles, tends to get even more "squishy".

 

[lysanderxiii]

If you look carefully at the Henry/Model 73 mechanism to can see two faces that prevent the toggle from rotating upwards (red arrows), and very careful measuring will show that the pins are not exactly at dead center.



The force of the chamber pressure tries to force the toggle to break in a way that moves the center pin upwards and the two faces marked resist that motion.

 

[Slamfire]

The whole intent of advanced ignition is to use the forward momentum of the bolt to resist the rearward thrust of the cartridge going off. The chamber pressure first has to stop the forward motion of the bolt, then start to accelerate it to the rear, allows a lighter bolt for the same power cartridge, or a more powerful cartridge with the same weight bolt.

It has been successfully used to make simple blow-backs as big as 83 mm....

I just skimmed the blowback section of Chinn's Vol IV "The Machine Gun". Chinn creates a category for "simple blowback", and "blowback with advanced primer ignition".

I went through the Oerlikon sections in Vol 1, Vol III and based on what I am reading, I was wrong to call the Oerlkon a delayed blowback. From all the descriptions it is a blowback with advanced primer ignition.

Buttress - (n) a projecting support.

The buttresses are the supports that prevent rotation beyond that desired.

Good pictures, I understand what you mean.

With all the pins, the pin holes, the forces on the pins and the holes, it seems to me that a toggle link breech is going to have wear issues compared to other breech mechanisms. I would also say, unlike a front locking action, the toggle breech carries the bolt thrust through a long load path, and that means the receiver has to be made of high strength materials for that distance, because the receiver has to resist the load of the toggle. This would be a more expensive design than something that uses a barrel extension, "trunnion", such as the AR-15 or HK 91. These mechanisms don't need an alloy steel receiver because the load path is kept within the front of the bolt and back of the barrel.

 

[RecoilRob]

Guys...this is one of those threads that makes me so happy to be here to absorb all of the points brought up. Good stuff and thanks.

 

[barnbwt]

Mostly it makes a gun heavy, like a Vickers or Maxim. Which is great, unless you need something that isn't a steam engine, in which case you have to drop the power levels & pressures or risk case distortion and wear issues.

TCB

 

[Kp321]

What has not been mentioned is the frame design of the toggle link rifles. The frame is an oval shaped piece of moderate strength metal. The side plates add no structural strength to the rifle. Every shot stretches the frame a little leading to permanent deformation of the softer (brass) frames or low cycle fatigue and cracking in harder frames.

 

[lysanderxiii]

With all the pins, the pin holes, the forces on the pins and the holes, it seems to me that a toggle link breech is going to have wear issues compared to other breech mechanisms. I would also say, unlike a front locking action, the toggle breech carries the bolt thrust through a long load path, and that means the receiver has to be made of high strength materials for that distance, because the receiver has to resist the load of the toggle. This would be a more expensive design than something that uses a barrel extension, "trunnion", such as the AR-15 or HK 91. These mechanisms don't need an alloy steel receiver because the load path is kept within the front of the bolt and back of the barrel.

M1/M14 vs FAL

M1898 vs Enfield

M16 vs SKS

There are many designs that use a relatively long distance between the breech face and locking shoulder.

The shorter the distance between the face of the breech and the locking face has a lot to do with the 'stretchiness' of the action. But, remember the M1918 BAR has a cast steel receiver and a long locking distance. Similarly, the number of joints added to the system makes for a 'squishy' action, but these are flexibility issues, not really strength issues.

 

[lysanderxiii]

Mostly it makes a gun heavy, like a Vickers or Maxim. Which is great, unless you need something that isn't a steam engine, in which case you have to drop the power levels & pressures or risk case distortion and wear issues.

TCB

Not really.

The Spandau air-cooled Maxim only weighed 22 pounds, 4 pounds less than an MG-34, and had about the same rate of fire, 900 rpm., and the MG08/15 (without water) weighed a tad less than the M1919A6....

The receiver of a Maxim or Vickers is mostly hollow:



Like I stated earlier, a toggle usually makes for a bulky action, because of the room needed for the toggle to fold and unfold.

 

[Slamfire]

M1/M14 vs FAL

M1898 vs Enfield

M16 vs SKS

There are many designs that use a relatively long distance between the breech face and locking shoulder.

With the exception of the M16, all of the firearms listed used all steel receivers. The FAL was a great rifle but it was expensive which is the primary reason it is out of inventory. When factory new FN's were last offered in the US, in the 1970's, adjusted for inflation the MSRP was $3,000. I asked a gun designer bud of mine about the FAL receiver and he said it was just as expensive to make as the M14. Both are made of high quality steel and are expensive to manufacture. As much as I love my M1a, that is a major reason why both of these designs are not going to ever be remanufactured and issued as a modern service rifle. Too expensive. However, the HK91 is still a front line 7.62 rifle and it was designed for cheap, rapid manufacture.

Every so often someone brings in a modern made Mauser 98 action and the things cost thousands of dollars. I have a high regard for the M98 but it is too expensive to make to be competitive on today's market, and that is also true of the Enfield.

There are lots of historical designs that functioned well but will never be put back into manufacture just because they are more expensive than the alternative.

 

[briansmithwins]

There are many designs that use a relatively long distance between the breech face and locking shoulder.

Yes, but there aren't very many (any that I can think of) new designs that use the receiver for locking. Using a barrel extension to take the firing loads just has so many advantages* that it's hard not to use it with a new design.

BSW

*Barrel extensions are lighter, smaller, cost less to make, and let you make the receiver out of sheet steel, aluminum, or even, dare I say it, plastic.

 

[lysanderxiii]

Yes, but there aren't very many (any that I can think of) new designs that use the receiver for locking. Using a barrel extension to take the firing loads just has so many advantages* that it's hard not to use it with a new design.

BSW

*Barrel extensions are lighter, smaller, cost less to make, and let you make the receiver out of sheet steel, aluminum, or even, dare I say it, plastic.

New? No, because these days we have cheap aluminum and plastics that can be used for "receivers"...

Incidentally, the basic Maxim design could be made with an aluminum (or, if beefy enough even plastic) receiver.... The firing loads are all taken by the long flat bar you see that the handle is mounted on and its mate on the other side, and the return spring is mounted on the other end of the handle's axle. The only thing of any strength on the missing side plate is the small button that cams the handle up to unlock the toggle (and that could be moved elsewhere if needed), the left side plate carries no load other than that of the spring. The only thing the big metal box does is house the trigger parts, and keep the dust out.

Similarly, the MP-44/StG-44's sheet steel receiver carries no real loads, the steel trunnion carries the major loads:



You could set that block in a sheet aluminum or molded plastic receiver and loose no strength (durability, maybe, but not strength). (NOTE: the MP-44 trunnion was made from pretty low grade steel, so it is bigger than if made from good steel.)

There are many advantages to the front locking lugs, most have to do with economy of material, ease of manufacture, rigidity, and weight, not really "strength" . . .

 

[lysanderxiii]

With the exception of the M16, all of the firearms listed used all steel receivers. The FAL was a great rifle but it was expensive which is the primary reason it is out of inventory. When factory new FN's were last offered in the US, in the 1970's, adjusted for inflation the MSRP was $3,000. I asked a gun designer bud of mine about the FAL receiver and he said it was just as expensive to make as the M14. Both are made of high quality steel and are expensive to manufacture. As much as I love my M1a, that is a major reason why both of these designs are not going to ever be remanufactured and issued as a modern service rifle. Too expensive. However, the HK91 is still a front line 7.62 rifle and it was designed for cheap, rapid manufacture.

Every so often someone brings in a modern made Mauser 98 action and the things cost thousands of dollars. I have a high regard for the M98 but it is too expensive to make to be competitive on today's market, and that is also true of the Enfield.

There are lots of historical designs that functioned well but will never be put back into manufacture just because they are more expensive than the alternative.

Original FAL receivers are made from 1060 steel, just a plain low alloy, high carbon steel, the same stuff the Germans were making K98k out of. Modern FALs use 4140, a good alloy steel, but even this does not have the tensile yield strength of 8620 that M1 and M14 receivers are made from (or M16 barrel extensions).

The receiver of a FAL can be made for less than 300-400 bucks, several places do just that. The rest of the parts would drive the price up, but to the tune of $2500? not likely. Not if done in high volume.

For the current limited market demand (one or two hundred per quarter), yes the price would be high, but that really does not mean the thing is unproducably expensive. Certainly not if done in volumes of 100 or 200 per week.

I guarantee these guys aren't loosing money making these things. So they are producing them for less than $300

 

[lysanderxiii]

Further:

You can buy a brand new rack grade M1A from Springfield for $1400. That includes SAI's profit, the wholesaler's profit, and the dealer's profit. So, the production cost are less, a lot less, then you throw in the fact that these are not done it high volume, currently less than 10,000 per year, probably a lot less.

The last contract for M14s from Olin was for 150,000 rifles and each cost $1000 (in 2015 dollars), that includes Olin's 10% profit per unit.

Is it a stretch to say that there is a $500 mark-up on M1As. I don't think so, probably more. But, at any rate, I think if there was a demand for 150,000 rifles per year, M1As, or FAL, could be made for much less than a grand each.

(Incidentally, around 2000, Colt was charging the USG over $1000 for an M4).

Current pricing for an M4A1 is around $700 per unit, an M14, or FAL, made today, in the volumes M4s are made (which benefits from high civilian sales of common parts, like bolts, bolt carriers, etc) wouldn't be all that uncompetitive.

 

[dpsurveyor]

Wow ! After reading all of this I feel like I should now be granted a degree in engineering of some sort. This has been a lot of fun reading everybody's response to the original post. Much appreciated, guys.

I now have a much better idea about what a toggle link does, what it can handle and why. I understand why I need to be very careful about reloads for my brass framed 1860 Henry. No overloads at any time or reason !

Thank you all.

dpsurveyor