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Locked breech vs. blowback

This is a discussion on Locked breech vs. blowback within the Pistols & Revolvers forums, part of the Pistol & Revolver Forum category; This subject came up recently in a discussion on which type of action would be easier for someone to use. I don't know that I've ...


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Old April 9th, 2013, 11:13 AM   #1
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Locked breech vs. blowback

This subject came up recently in a discussion on which type of action would be easier for someone to use. I don't know that I've come up with a definitive answer to that question, but it made me realize... I didn't really know what these terms really meant. I, like apparently many others, thought that all semi auto pistols were blowback pistols. WRONG! But it is a logical conclusion based solely on the terms themselves.

I'm going to share some of what I've discovered about the subject but certainly don't claim to be an expert on the subject. Maybe we can get some of our resident experts to chime in.

First, most modern pistols fall into one of these two categories, blowback or locked breech (also referred to as tilting barrel, delayed blowback or recoil). Note: Dessert Eagle pistols are a whole 'nother subject!

The obvious difference is probably in how the barrel is attached to the gun. Blowback pistols have the barrel attached to the frame itself. Locking breech pistols have the barrel housed in the slide along with the recoil spring guide rod and recoil spring.

Based on this difference, the blowback system is inherently more accurate, but modern manufacturing techniques have virtually illiminated that difference. Also, the blowback system has nothing to absorb the shock of the recoil except the slide and the small parts inside. This requires a much heavier slide than a locked breech system which in turn generally means the overall weight of the gun is heavier than a locked breech system.

Locking breech systems or sometimes called delayed blowback systems, do just that. In the blowback system the strength of the the recoil spring prevent the pressure of the burning gasses from escaping from the side of the casing.

A couple of examples of these types of pistols would be the:

The Walther PPK - Blowback



The 1911 - Locked Breech



As you can see in the schematics, the 1911's barrel is a separate part while the Walter PPK's barrel is integrated with the frame.

Because the blowback design has an integrated barrel and frame, the felt recoil on this design is significantly stronger than the locking breech design.

In the Locked Breech or Tilting Barrel design, when the slide is fully into battery, the barrel locks by means of lugs, that lock into place so that while it's in that position, the barrel and frame are essentially locked together. This is what allows the tilting barrel design to be accurate.

Both sytems, when functioning properly, keep the base of the casing forced against the chamber until the spent bullet exists the barrel. Then the pressure is released and the case ejection process begins.

With the locking breech (tilting barrel/delayed blowback), once enough time has elapsed for the bullet to exit the barrel, the locking mechanism disengages, unlocking the barrel and in most cases allows the barrel to tilt to aid in the loading of the next round. Not all modern locking breech systems use the tilting barrel design, for example the Beretta 92 uses a rotating barrel design.



Another popular design, though I don't know of any currently in production, is the Luger P-08 design, which doesn't even have a slide, but uses a toggle instead. By the definition I've described here, I'm guessing it's considered a blowback design, as well.



However, with my research, I've still not fully answered the question of which design would be easier to use. The locked breech/recoil/tilting barrel design generally has less recoil than a blowback. But because of the mechanics of the designs, blowbacks generally speaking, are relegated to lower caliber cartridges. The reason being that in larger calibers, the strength of the recoil springs and weight of the slide usually become unacceptable. One exception is that Browning has made higher caliber blowback designs, up to and including the .45ACP.

It would seem so far, that the locked breech design gets the edge for shootability while a slight accuracy edge goes to the blowback. Blowbacks are inherently heavier and generally the smaller the caliber, the less felt recoil.

So, the last piece of missing information (that I can think of), is the actual strength required to rack a round into the chamber. While I do have a Luger P-08, I don't have, nor have I ever used, any other blowback designs (excluding the 10/22, which is a blowback design, but obviously not - charger excluded - a pistol).

This topic is pretty interesting, but I was amazed at how much I didn't know, and probably still don't know about it.

I'd like to hear others comment here, as well. I don't care if you know nothing about it or you're an old, sage gunsmith. I think it's an important bit of information pistols shooters should be aware of and a topic that's generally not discussed very much.




Last edited by jlh820; April 9th, 2013 at 01:00 PM.
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Old April 9th, 2013, 11:54 AM   #2
 
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Thanks for the post. It was informative.
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Old April 9th, 2013, 02:40 PM   #3
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jlh820, John Moses Browning invented the "delayed blowback" design (which you call a "locked breach") when he designed the Colt Model 1905 (predecessor to the 1911) . This design has been copied by just about every pistol manufacturer in the world.

The "straight blowback" design is restricted to lower power cartridges such as a 22 LR, 25 ACP, 32 ACP, or 380 ACP. Some cheap 9mms also use straight blowback. Straight blowback can use either a slide (like a Ruger LCP) or an internal bolt (like a Ruger Mark Series). The reason why the straight blowback design is not used in higher power pistols is the recoil spring would have to be so strong it would take a gorilla to pull the slide or bolt back plus the slide would be very heavy.

The "delayed blowback" design (AKA locked breach) operates much the same as a "straight blowback" design where barrel pressure from the fired cartridge generates enough thrust to push the slide (or bolt) back to eject a spent case and feed a new round. The difference is ... the lock lugs on a delayed blowback design hold the barrel in position until after the bullet exits the muzzle. The sudden change in pressure causes the barrel to unlock, yet there is still enough barrel pressure to operate the slide. The German P-08 Luger uses a two piece "toggle bolt", which is also a delayed blowback design. The advantage of a delayed blowback design is simply the tension of the recoil spring where most of the thrust energy is contained by the slide, thus a much lighter recoil spring is used.

With a straight blowback design, the bolt or slide begins to move as soon as chamber pressure begins to peak (about an inch of bullet travel). Because the slide/bolt is much heavier than the bullet and has a strong recoil spring, it moves much slower than the bullet so the bullet will exit the muzzle before the bolt/slide move very far. Once the bolt/slide begin to move, continuous barrel pressure and momentum will cause it to thrust back. Straight blowback centerfire pistols require a very heavy recoil spring coupled with a heavy slide. With exception of Hi-Point brand 9mms, nearly all 9mm, 38 Super, 40 S&W, and 45 ACP pistols use the delayed blowback design. Some use a barrel link to drop the barrel whereas others use a cam block. Both accomplish the same mission ... just a different approach.

As mentioned above, there is a third design .... gas operated. These work just like a Ruger Mini-14 and are restricted to just Desert Eagles where there is a small hole in the barrel (gas port) that drives a piston to operate the slide.
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Old April 9th, 2013, 02:55 PM   #4
 
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It has been my experience that "blowback" pistols, due to their necessarily heavy recoil springs, can be very hard to cock. Particularly for those with less hand strength due to gender, age, or other factor.
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Old April 9th, 2013, 03:52 PM   #5
 
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Quote:
Originally Posted by Iowegan View Post
jlh820, John Moses Browning invented the "delayed blowback" design (which you call a "locked breach") when he designed the Colt Model 1905 (predecessor to the 1911) . This design has been copied by just about every pistol manufacturer in the world.

The "straight blowback" design is restricted to lower power cartridges such as a 22 LR, 25 ACP, 32 ACP, or 380 ACP. Some cheap 9mms also use straight blowback. Straight blowback can use either a slide (like a Ruger LCP) or an internal bolt (like a Ruger Mark Series). The reason why the straight blowback design is not used in higher power pistols is the recoil spring would have to be so strong it would take a gorilla to pull the slide or bolt back plus the slide would be very heavy.

The "delayed blowback" design (AKA locked breach) operates much the same as a "straight blowback" design where barrel pressure from the fired cartridge generates enough thrust to push the slide (or bolt) back to eject a spent case and feed a new round. The difference is ... the lock lugs on a delayed blowback design hold the barrel in position until after the bullet exits the muzzle. The sudden change in pressure causes the barrel to unlock, yet there is still enough barrel pressure to operate the slide. The German P-08 Luger uses a two piece "toggle bolt", which is also a delayed blowback design. The advantage of a delayed blowback design is simply the tension of the recoil spring where most of the thrust energy is contained by the slide, thus a much lighter recoil spring is used.

With a straight blowback design, the bolt or slide begins to move as soon as chamber pressure begins to peak (about an inch of bullet travel). Because the slide/bolt is much heavier than the bullet and has a strong recoil spring, it moves much slower than the bullet so the bullet will exit the muzzle before the bolt/slide move very far. Once the bolt/slide begin to move, continuous barrel pressure and momentum will cause it to thrust back. Straight blowback centerfire pistols require a very heavy recoil spring coupled with a heavy slide. With exception of Hi-Point brand 9mms, nearly all 9mm, 38 Super, 40 S&W, and 45 ACP pistols use the delayed blowback design. Some use a barrel link to drop the barrel whereas others use a cam block. Both accomplish the same mission ... just a different approach.

As mentioned above, there is a third design .... gas operated. These work just like a Ruger Mini-14 and are restricted to just Desert Eagles where there is a small hole in the barrel (gas port) that drives a piston to operate the slide.
It's all good, except the portion in red.

Recoil is recoil and the slide and barrel, while still locked together, begin to move aft as soon as the round is fired. In any pistol, delayed blowback or straight blowback, the bullet, due to higher velocity and lower mass has left the barrel before the slide really begins to noticeably move. The difference is that with a delayed blow back design like the 1911, the barrel and slide move back together as a locked unit until (in the case of the 1911) the slide and barrel move back far enough relative to the frame that the barrel link then pivots the locking lugs on the barrel down out of engagement with the locking recesses in the slide. By that time the pressure is low enough in the barrel for the cartridge to be released from the chamber walls, and the slide has sufficient momentum to fully cycle the pistol.

With the blow back pistol the same thing has to happen in terms of the pressure in the chamber being low enough to have allowed the case to release from the chamber walls, and that's accomplished only by the mass of the slide and the resistance of the spring, with no mechanical delay. So for a higher powered round like the 9mm Luger or .45 ACP, you need a heavy slide and a heavy recoil spring.

Those are common features on blow back operated sub machine guns like the M3, the Sten, the MP40, the Thompson and the Uzi, which are chambered in 9mm Luger or .45 ACP. In those designs the cyclic rate is controlled by the weight of the bolt and the strength of the recoil spring (which needs to remain strong enough to operate the bolt swiftly enough to fire the first round under spring pressure alone with no rebound from the bolt, as most blow back SMGs operate from an open bolt, with either a fixed firing pin or an inertial firing pin. The Uzi combines a heavy bolt in a short over all length by having the bolt telescope over the barrel, letting the overall weapon be shorter.

Newer SMGs can be lighter due to the use of a delayed blowback system, such as the roller locking system on the MP5, or gas operated like the Colt 9mm SMG, or at least put the weight of the weapon somewhere more useful, and it allows for control of the cyclic rate by other means.
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Old April 9th, 2013, 05:03 PM   #6
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Thanks, Iowegan! I was hoping you would reply. Your posts are always appreciated and very informative.

Looks like I got it mostly right. . I took a shot in the dark on the Luger P-08 since I couldn't find any info regarding it. It's a very unique design!

I haven't done a lot of research on Dessert Eagles but thought they used a system similar to the AR DGI system.

My purpose in posting this was to stir some discussion about these designs, learn from others and help others to learn as well.

If someone had asked me last week to define a blow back system, I wouldn't have had a clue. I do know that Browning's 1911 design is the most copied pistol design in the world.

Thanks, again.
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Old April 9th, 2013, 05:05 PM   #7
 
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Very well done explanation for those who did not understand the difference.
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Old April 9th, 2013, 05:07 PM   #8
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Quote:
Originally Posted by NewportNewsMike View Post
It has been my experience that "blowback" pistols, due to their necessarily heavy recoil springs, can be very hard to cock. Particularly for those with less hand strength due to gender, age, or other factor.
Thanks, that was what I suspected. What spurred my investigation was a comment someone made that seemed to advocate a blowback type pistol for someone with weaker hands. That didn't ring true to me, so I started digging.
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Old April 9th, 2013, 05:17 PM   #9
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Okay then, could you make a delayed blowback .22LR pistol? Would be very easy to rack, if nothing else. I know the LCP is a tilted barrel design, making a small .380 more comfortable.
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Old April 9th, 2013, 05:19 PM   #10
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Model 52, thanks for the clarification. This was my understanding, too. Though my knowledge of machine guns is extremely limited. I've got a pretty good knowledge of the AR-15/M-16 and a little about the AK. I've never had the opportunity to shoot or dismantle a machine gun or SMG. Though the MG-42 fascinates me.
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Old April 9th, 2013, 05:21 PM   #11
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Originally Posted by bearcatter View Post
Okay then, could you make a delayed blowback .22LR pistol? Would be very easy to rack, if nothing else. I know the LCP is a tilted barrel design, making a small .380 more comfortable.
Again, no expert here, but isn't that what the SR-22 is (the pistol).
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Old April 10th, 2013, 09:34 AM   #12
 
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Originally Posted by jlh820 View Post
Again, no expert here, but isn't that what the SR-22 is (the pistol).
The SR22 uses a barrel that is fixed to the frame, thus making it a blowback design.
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Old April 10th, 2013, 09:48 AM   #13
 
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Quote:
Originally Posted by bearcatter View Post
Okay then, could you make a delayed blowback .22LR pistol? Would be very easy to rack, if nothing else. I know the LCP is a tilted barrel design, making a small .380 more comfortable.
Twisted Industries has a 22LR conversion for the LC9 coming soon. It will obviously be a Locked Breech type pistol. It will be interesting to see how well it works. They have conversions for the Kel-Tec 9mm pistols and the comments from users are positive. Are there any 22 LR Locked Breech pistols?
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Old April 10th, 2013, 10:18 AM   #14
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The SR22 uses a barrel that is fixed to the frame, thus making it a blowback design.
Hmmm, I thought I checked the schematic on that. I'll have to check again.
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Old April 10th, 2013, 12:53 PM   #15
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jlh820, The Luger P-08 is quite a marvel when it comes to design. When the toggle bolt is closed (in full battery) it acts much the same as a normal delayed blowback pistol where the barrel lugs lock into the slide. As the gun recoils, the bolt will release and be blown back. This design also allows a pretty soft recoil spring with a light weight bolt. I'm really surprised other gun manufacturers haven't used a similar toggle bolt design.

I used to own a pair of Desert Eagles ... one in 44 Mag and the other in 357 Mag. Both had a gas port in the barrel just a fraction of an inch from the muzzle. This will syphon off just enough gas pressure to operate the piston and in turn, thrust the slide back. Works just like most gas operated rifles. To the best of my knowledge, Desert Eagles are the only gas operated pistols on the market. The Baby Eagle uses a conventional delayed blowback design.

Weblance,
Quote:
Are there any 22 LR Locked Breech pistols?
I've never seen a 22 LR with delayed blowback (locked breach). I suppose it could work but there isn't much thrust generated by a 22 LR so I don't think it would be very successful ... probably very ammo fussy, which is probably why all manufacturers use a straight blowback design with 22 semi-autos.

I doubt if the LC9 22 LR conversion kit will use a locked breach (delayed blowback) design. All other 22 LR conversion kits I've seen (ie Colt Ace, Kimber 1911, Beretta 92, etc) use a straight blowback design. I have one of the older Colt Ace kits and it has an interesting 2-piece barrel. Carbine Williams designed it to operate like a piston to operate a heavier steel slide. Unfortunately, it only works for 40~50 rounds before it gets corrupted with powder residue, then fails to function until you clean it. My 1911 Kimber and Mod 92 Beretta conversion kits have much lighter aluminum slides, a one piece barrel, and use a straight blowback design ... no lock lugs on the barrel or slide. These work much better than the Colt Ace ... more accurate and you don't have to stop and clean them every 40~50 rounds. All 22 conversion kits require a different slide, barrel, recoil spring, and magazine than the parent pistol. In other words, the only thing that remains the same is the lower frame.

Last edited by Iowegan; April 10th, 2013 at 12:57 PM.
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