Why not a blowback .223 semi-auto rifle?

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I'll add this to the discussion. A direct blowback intermediate rifle is something that has already been tried, and seemed to work OK in the form of the Volksstrumgewehr lines from the end of WW2. Ian at forgotten weapons had the chance to shoot one and judging by everything he said, it seemed to have worked just as well as the StG44. While it is listed as a "gas delayed blowback" as Ian comments,it is highly questionable if that particular system actually ended up doing anything and by and large the gun functions as a direct blowback rifle.
 
V, thanks for the link. Very interesting. Now I'm even more convinced that this could work. Imagine how much better this could be done using modern materials.
 
You could make it work, as in you could get it to operate with a restricted range of bullet weights, but you still won't have the same safety margin as you would in a locked breech gun. And to get it to operate safely with all commercial loads, you'd likely have to sacrifice functionality with the lighter bullet weights.

So could you make it functional as in "Hey look, it shoots if I restrict the ammo to only these bullet weights!"? Yeah, I think so. Would it be "workable" as in "reasonably practical". No.
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Actually, it would be fine to sacrifice functionality with lighter bullets. They're typically only used for long range varmint hunting, and this gun wouldn't be a good choice for that anyway. It doesn't really need to handle anything over 70 gr either, as bullets that heavy are rather specialized items. It would probably only really need to work well with bullets in the 55-69 gr range. That's what most people would shoot anyway. I don't know if there would be a safety issue with heavier bullets, but there's no reason to assume it. The difference in bolt velocity between a 55 gr and 77 gr bullet wouldn't be that much.
 
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If you get a chance, take a look at the FN 5.7. 5.7 operates at similar peak pressures to .223, the 5.7 is ~50,000psi, the .223 is ~55,000psi. The AR57 upper is a direct blowback rifle system and it beats the heck out of your brass. Shoulders are blown forward significantly, like this:
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Case splits are not uncommon. I'm not trying to bash the round or the idea, I love my AR57, but the idea of a .223 blowback scares me. .223 develops much larger velocities by holding that peak pressure longer, which would do even more damage to the brass. Fluted chambers don't make that issue go away either; it takes time for the gas to flow and pressure to equalize, it doesn't happen instantly. For a good read on the subject check out this book: http://www.amazon.com/Ballistics-Th...TF8&qid=1349309131&sr=1-5&keywords=ballistics. I've been slogging my way through it and it's impressive how large a pressure differential you can have between the gas right behind the bullet and the gas in the case.

Panzercat said:
As a side note, a Hi-Point .40 was successfully rebored and modified to fire 10mm without any issue whatsoever.
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True, but 40 and 10mm are much closer in performance than .223 and 5.7 or .223 and 9mm. The fact that both are straight walled cases also makes them much more compatible with a blowback system.
 
Jon_Snow: Valid point, but I don't think having a recovered cases that you can reload was/is much a concern of this thought experiment. If the case gets trashed after the first use, its not much of an issue. Also, what about the use of say Russian Steel Case ammo? I doubt the shoulder creep problem or split cases would be as much of an issue, since you're not going to be reloading those cases anyway.

Plus I think its a foregone conclusion that a strait blowback .223 rifle is going to have various shortcomings versus a breach-locking rifle, the more interesting question here is can it be done, and how well will it work.

Thinking of the issue of case support and blow back, I don't see any reason why you couldn't use an overly long fluted chamber with a bolt that telescopes INTO the chamber, so that when the system begins to move back under recoil, the case is still supported by the chamber for a good bit of its travel until pressure drops to a more managable level and the case ejects out the side. To this extent, I also wonder if an extractor is even needed, since the case will be driving the whole system back as soon as it fires and will not be "pulled out" of the chamber. Thus, all that is needed is a fixed ejector to kick the case out the side. If I recall correctly, the HK P7 is well known for being able to function just fine with the extractor completely removed from the system, and it also uses a gas-delayed direct blowback system.
 
Case splits are not uncommon. I'm not trying to bash the round or the idea, I love my AR57, but the idea of a .223 blowback scares me. .223 develops much larger velocities by holding that peak pressure longer, which would do even more damage to the brass. Fluted chambers don't make that issue go away either; it takes time for the gas to flow and pressure to equalize.
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Yup. And it's tricky to reload for because the bolt timing and pressure curve have to be worked out carefully to prevent catastrophic incidents. The same problems would be encountered with the .223, but amplified. Not only for the reason you point out but also because there's a much wider range of bullet weights and commercial loadings that need to be accommodated safely.
thanks for the link. Very interesting. Now I'm even more convinced that this could work. Imagine how much better this could be done using modern materials.
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The bolt/slide on that gun reportedly weighs upwards of 6lbs--about twice what should be required based on the method you used for calculating the bolt weight required for a .223 rifle. Even so, the designers felt the need to add a delaying system.

So, given that you're convinced a blowback .223 is a viable design, how do you account for the fact that no one is making or selling such an animal?
 
JohnKSa said:
Yup. And it's tricky to reload for because the bolt timing and pressure curve have to be worked out carefully to prevent catastrophic incidents. The same problems would be encountered with the .223, but amplified. Not only for the reason you point out but also because there's a much wider range of bullet weights and commercial loadings that need to be accommodated safely.The bolt/slide on that gun reportedly weighs upwards of 6lbs--about twice what should be required based on the method you used for calculating the bolt weight required for a .223 rifle. Even so, the designers felt the need to add a delaying system.

So, given that you're convinced a blowback .223 is a viable design, how do you account for the fact that no one is making or selling such an animal?
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For the same reason you didn't see many mass marketed higher caliber blowback pistols prior to hi-point-- It's an inefficient, unwieldy design that manufactures assumed wouldn't have a place in the market with consumers...

...Except when your price point is somewhere between "Dirt" and "Cheap".
 
Sten and Sterling SMG bolts are light

Re: the need to use a very heavy bolt/spring combo in a delayed blowback high-pressure firearm.

Many SMGs rely on a delayed blowback system without the heavy bolt/spring.
Pulling the trigger on a 9mm Sten, Stirling releases the cocked-back bolt which then picks up a round and slamfires it as the bolt is still closing. The bolt's forward momentum plays an important part in delaying bolt blowback till chamber pressure drops.
 
Right, in an open-bolt design you can substitute momentum for inertia and spring force by having the cartridge fire before it's actually fully chambered. Works best with relatively low-pressure cartridges for obvious reasons.

From a practical perspective, that's not a viable option for the U.S. market since the BATF frowns on open-bolt semi-auto designs.
It's an inefficient, unwieldy design that manufactures assumed wouldn't have a place in the market with consumers...

...Except when your price point is somewhere between "Dirt" and "Cheap".
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All correct. Except that there are obviously manufacturers who design and sell to that price point--and yet we still don't see them turning out blowback .223 rifles. So that doesn't quite answer the question.
 
So, given that you're convinced a blowback .223 is a viable design, how do you account for the fact that no one is making or selling such an animal?
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Because it would be inferior to the proven designs that are already available. When I said it was workable, I only meant that it could be made to work. I never said that it would be commercially viable.
 
Because it would be inferior to the proven designs that are already available.
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The Hi-Point pistols are inferior to proven designs already available and yet they are made and sold in great numbers, apparently to the satisfaction of both the manufacturer and at least a significant percentage of buyers.

In other words, the fact that a design is accepted to be inferior to other available proven designs doesn't keep a gun from being made and sold nor from being commercially viable.

Ok, that aside, how do you explain that the bolt/slide on the rifle in the link that -v- provided is reportedly about twice as heavy as your calculations suggest is required and yet the designers still added a delay mechanism?
 
Ok, that aside, how do you explain that the bolt/slide on the rifle in the link that -v- provided is reportedly about twice as heavy as your calculations suggest is required and yet the designers still added a delay mechanism?
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Reportedly? The only place I could find this weight reported was in a blog where they were just basing the weight on a calculation. They didn't actually weigh it. The guy in the video said that the guess sounded reasonable, but he didn't weigh it either. Their estimate could easily be a pound or two off. The 7.92 x 33 has twice the bullet weight of a typical .223. so it would need a much heavier bolt. Based on plugging the numbers into the recoil calculator, it's should weigh at least 3 lbs. I wouldn't be surprised if it weighed 4 or 5 lbs. The extra weight certainly wouldn't hurt its reliability. Even if it did weigh 6 lbs., this would only suggest a 4 lbs bolt for the .223. Pretty heavy, but still doable.

The delay mechanism would have had little if any affect. The gas ports were near the muzzle, so it wouldn't have done anything at all to prevent the action from starting to open early. All it would do is increase the effective spring pressure later in the cycle. This might help buffer the recoil when using higher pressure loads.
 
The Hi-Point pistols are inferior to proven designs already available and yet they are made and sold in great numbers, apparently to the satisfaction of both the manufacturer and at least a significant percentage of buyers.

In other words, the fact that a design is accepted to be inferior to other available proven designs doesn't keep a gun from being made and sold nor from being commercially viable.
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They took a gamble and it worked out. They did this relatively recently. How come nobody was selling something like the Hi-Point 30 years ago? Because improvements in technology (synthetic frames in particular) made it more practical. Also, a blowback pistol isn't all that unusual. There have been been blowback pistols is slightly milder rounds for ages.

Anyway, the shortcomings of a blowback .223 would probably be worse than a 9mm pistol. I doubt it would sell well.
 
Jon Snow, does the AR57 have a fluted chamber?
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No, it doesn't but I remain unconvinced that it would help. I does however have a bolt that weighs about twice what a .223 BCG weighs. I'll weigh both when I get home tonight.

Jon_Snow: Valid point, but I don't think having a recovered cases that you can reload was/is much a concern of this thought experiment. If the case gets trashed after the first use, its not much of an issue. Also, what about the use of say Russian Steel Case ammo? I doubt the shoulder creep problem or split cases would be as much of an issue, since you're not going to be reloading those cases anyway.
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I wasn't concerned about being able to reload the cases afterwards, I'm concerned about rupturing them during extraction. Restricting the gun to steel cased ammo only might solve the problem, but I'd still be cautious.

In other words, the fact that a design is accepted to be inferior to other available proven designs doesn't keep a gun from being made and sold nor from being commercially viable.
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I'm going to play devil's advocate for a moment. Typically, companies don't make things unless they are commercially viable. That means that they must believe that whatever loss in perfomance they have due to a sub-optimal design must be counter-acted by a matching drop in sale price. The fact that no one has commercially produced a blowback .223 just means that the preformance loss wouldn't match a potential price reduction. In short, even if you can make something work, if no one would buy it then no one will make it.
 
One glaring problem with the analysis in the posted link:
The basic problem here is that though the pressure pushing the bullet and bolt are equal, the areas are not equal. Cartridges are always at least a little bigger at the back end, and sometimes much bigger. This causes "bolt thrust" issues with the new short fat cartridges like 300 WSM, even at quite reasonable chamber pressures. In fact, unlike Chinn, I'm going to ignore the gas momentum and start out by assuming:
pressure on bolt face = pressure on bullet back
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As I said in my earlier post, the pressure on the bolt != pressure accelerating the bullet. The chamber pressure is higher, sometimes significantly. So his theoretical bolt weights are too low.
 
An other for blowback pieces of evidence. The Thompson Blish lock rifle which used the Blish lock phenomenon with a rotating non-locked blowback bolt design. Lately it has been noted that dissimilar metals moving against each other under high pressure demonstrate fluid-like behavior, so that accounts for the increased friction vs predicted.

(Link to TFB article about this and the Thompson auto-rifle)

The rifle worked as basically as a blowback rifle, where as soon as the cartridge fired, it would push the bolt back and the bolt would begin to rotate it. Some of the rotation of the bolt and increased friction from the blish phenomena helped to slow the bolt down and give a greater "holding" power then just a strait blow-back or mass. This was by the way with a .30-06 and 7.62x54r and not a .223, so significantly MORE bolt-thrust then what a .223 would deliver. Also, this rifle did need lubricated cases, but that is not anything that can't be solved with chamber fluting, as they serve the same purpose.

Again, I offer historical evidence for consideration that blowback rifle have been made, and they have worked safely.

And to re-iterate, for this discussion, when we are talking about blowback, we mean a system where the bolt is not locked to the barrel, and requires a separate outside mechanical force to unlock it, be it direct gas impingement, short or long recoil operating rod, or in the case of the G3 a second recoiling mass.
 
Reportedly? The only place I could find this weight reported was in a blog where they were just basing the weight on a calculation.
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Poking around, I found two other sources which both estimated the weight as being 6 or 7 lbs.
The 7.92 x 33 has twice the bullet weight of a typical .223. so it would need a much heavier bolt.
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If you calculate the momentum, it's more, but it's not nearly enough to get the bolt weight up into the 6-7 lb range. The velocity is much lower which helps to counterbalance the effect of the heavier bullet.
He comes up with a bolt weight for a blowback .223 of around 7 pounds to keep extraction reasonable.
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Which, combined with the estimates of the German rifle's bolt/slide weight makes it clear why the designers added a delay mechanism in addition to the already significant bolt weight given the additional momentum that the German rifle had to deal with compared to a .223.
The rifle worked as basically as a blowback rifle, where as soon as the cartridge fired, it would push the bolt back and the bolt would begin to rotate it. Some of the rotation of the bolt and increased friction from the blish phenomena helped to slow the bolt down and give a greater "holding" power then just a strait blow-back or mass.
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The rifle worked basically as a blowback rifle with a mechanical delay based on the Blish lock phenomenon. Which is to say it worked as a delayed blowback rifle. It's been pretty well established that delayed blowback can be practically workable in rifles--and there are a number of ways to accomplish that delay including the Blish lock phenomenon.
 
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Okay, I've been studying this bolt weight issue and I've concluded that my previous assumptions were wrong. It probably does need to be around 6 lbs. It might be possible to get away with a bit less, but 6 lbs. is in the right ballpark. I think the 7 lbs estimate in the one blog is overkill though. He based that on an 80 gr bullet at nearly 2900 fps, which is not realistic from a 16" carbine barrel. Also his assumption that the bolt velocity needs to be no more than 12 fps is questionable. Many blowbacks have far high bolt velocity.

A 6 lbs bolt certainly makes this less practical and should discourage manufacturers from pursuing this as a product. However, it is still quite possible to make a carbine with a bolt this heavy and still have an overall weight of less than 10 lbs. You would have to use a lot of polymer parts and a thin barrel profile. So it's still workable. But having a gun with more than half its weight in the bolt would make for really poor handling qualities.

And a big thank you to everyone for the interesting discussion!
 
There actually have been straight blowback sporting arms firing rather hefty cartridges; the Winchester Self Loading designs from around a century ago:

http://en.wikipedia.org/wiki/Winchester_Model_1910

Cartridge for the largest ones was the .401 WSL, capable of flinging a 200 grain bullet at 2150 FPS. Not shabby.

(What genius came up with the wholly misleading and useless term "inertia delayed blowback?")
 
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