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BarnOwlLover

HK433 Generation 5

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This is one modern rifle that I'm insanely interested in, especially since there was a TFB article that hinted that there was a .308 Winchester/7.62mm NATO version being worked on that might use the same upper as the 5.56mm NATO version that HK has shown in several different versions since 2017. 

 

This is the latest (known) iteration of the 433, and if you've seen some of the POTD posts at TFB since May of last year, you've probably seen it a time or two.  In short, the 433 is HK's answer to the FN SCAR and to try and one up it.  IMO, the most interesting thing about the 433 is that it seems capable of taking way more caliber rounds than items such as the FN SCAR or the Bren 2, which needed new uppers in order to go rounds like .308. 

 

Out of curiosity one day, since I've seen numerous (though not often very new) photos of the 433 and I've also seen patent documents (I'll provide a link to patent documents and an article on Spartanat with some photos of the Gen 5 433), I decided to see if my own thoughts on the 433 being caliber convertible beyond .300 Blackout or 7.62x39mm held water.  Using a simple image scaling and measuring program, I've determined that the 433 upper, as is, is capable of taking rounds or at least magazines of 71-72mm OAL.  Mind you, this isn't exact, and I was conservative with my measurements. 

 

Of course, this does further peak my curiosity on what the 433 is capable of firing and how caliber convertible it may be.  On top of of course how it comes apart and various details about it.

 

Now the documentation.  Spartanat is an Austrian site, and hence is in German, and being new here I'm not sure how Google translate works when linked, so I'll just leave the link (which has good, albeit sadly not ultra HQ/high res images, which IMO is a damn shame) to be copypasta'd into Google's translator or your favorite translator.  On the plus side, there's a PDF in the article that you can save or convert to a pretty high res JPG or PNG image, and Google does a decent job of translating the PDF, too:

 

https://www.spartanat.com/2019/05/photo-file-hk433-mit-concamo-im-feld/

 

Now here's the patent documents and images.  This series mostly pertains to the charging handle system, but it shows a good idea of how the guts of the 433 are laid out:

 

https://patents.google.com/patent/DE102018001984A1/en?inventor=Wilhelm+Fischbach

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1 hour ago, BarnOwlLover said:

This is one modern rifle that I'm insanely interested in, especially since there was a TFB article that hinted that there was a .308 Winchester/7.62mm NATO version being worked on that might use the same upper as the 5.56mm NATO version that HK has shown in several different versions since 2017. 

 

This is the latest (known) iteration of the 433, and if you've seen some of the POTD posts at TFB since May of last year, you've probably seen it a time or two.  In short, the 433 is HK's answer to the FN SCAR and to try and one up it.  IMO, the most interesting thing about the 433 is that it seems capable of taking way more caliber rounds than items such as the FN SCAR or the Bren 2, which needed new uppers in order to go rounds like .308. 

 

Out of curiosity one day, since I've seen numerous (though not often very new) photos of the 433 and I've also seen patent documents (I'll provide a link to patent documents and an article on Spartanat with some photos of the Gen 5 433), I decided to see if my own thoughts on the 433 being caliber convertible beyond .300 Blackout or 7.62x39mm held water.  Using a simple image scaling and measuring program, I've determined that the 433 upper, as is, is capable of taking rounds or at least magazines of 71-72mm OAL.  Mind you, this isn't exact, and I was conservative with my measurements. 

 

 

Could you show us these measurements?

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Measurements are in millimeters.  Upper measurement is OAL, lower measurement is length of the rear of the front trunnion to approx end of mag well:

 

https://i.imgur.com/sNOUg7p.png

 

The position of the TE of the rear turnnion was determined from this:

 

https://i.imgur.com/3NysHxH.png

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So, even assuming that the trunnion to the rear of the magazine well is the primary limitation of the size of cartridge a rifle can handle, why do you think that two milimeters is going to make all the difference?


qL8BIoU.png

 

Look carefully at this comparison of a SCAR-L with a SCAR-H.

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The thing that has to be remembered is that the SCAR was broken up into the L and H variants, or basically 5.56mm and 7.62mm NATO.  The H has an upper that's nearly an inch longer than the L variant, let alone much wider.  Also, considering that most of the caliber conversions (such as 7.62x39) have focused on the H variant, I've wondered and come to think that the L is optimized around 5.56mm.  I actually can't remember there being any caliber conversions offered for the SCAR 16 aside from .300 Blackout. 

 

What has gotten me thinking about the 433 maybe being 7.62mm NATO compatible with a lower, barrel and bolt swap is, one, the TFB article referring to it.  But I've also been told on HK Pro that, for instance, HK were shown or at least informed of the concept of the POF .308 chambered AR-15 upper.  That's what got me thinking about seeking out an online image scaler/measure feature. 

 

Which brings me to Sturgeon saying that it's well within margin of error.  Emphasis on the word error on my part.  I'm very, very doubtful that my measurements are exact.  Also, I haven't been able to locate the length front to rear of a .308 HK mag or SR-25 mag.  Granted, I've measured a few photos of the 433 in the same method, and though the measurements haven't come out exactly the same each time, they've fallen into the same 71-72mm range.  Which given variations in photos, my un-steady hands and crappy eyesight, can maybe be considered a preponderance of evidence (?). 

 

Of course, if the 433 can take .308/7.62mm sized rounds in terms of width and length, that can open up a lot of things, given that the 433 would be a pretty compact rifle for barrel length in those larger calibers. 

 

Granted, all the 433's that have been show are not only in 5.56mm, but are marked as 5.56mm on the upper, though the rifles shown are basically the versions they're trying to pitch to the German Army.

 

 

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12 hours ago, BarnOwlLover said:

The thing that has to be remembered is that the SCAR was broken up into the L and H variants, or basically 5.56mm and 7.62mm NATO.  The H has an upper that's nearly an inch longer than the L variant, let alone much wider.  Also, considering that most of the caliber conversions (such as 7.62x39) have focused on the H variant, I've wondered and come to think that the L is optimized around 5.56mm.  I actually can't remember there being any caliber conversions offered for the SCAR 16 aside from .300 Blackout. 

 

What has gotten me thinking about the 433 maybe being 7.62mm NATO compatible with a lower, barrel and bolt swap is, one, the TFB article referring to it.  But I've also been told on HK Pro that, for instance, HK were shown or at least informed of the concept of the POF .308 chambered AR-15 upper.  That's what got me thinking about seeking out an online image scaler/measure feature. 

 

Which brings me to Sturgeon saying that it's well within margin of error.  Emphasis on the word error on my part.  I'm very, very doubtful that my measurements are exact.  Also, I haven't been able to locate the length front to rear of a .308 HK mag or SR-25 mag.  Granted, I've measured a few photos of the 433 in the same method, and though the measurements haven't come out exactly the same each time, they've fallen into the same 71-72mm range.  Which given variations in photos, my un-steady hands and crappy eyesight, can maybe be considered a preponderance of evidence (?). 

 

Of course, if the 433 can take .308/7.62mm sized rounds in terms of width and length, that can open up a lot of things, given that the 433 would be a pretty compact rifle for barrel length in those larger calibers. 

 

Granted, all the 433's that have been show are not only in 5.56mm, but are marked as 5.56mm on the upper, though the rifles shown are basically the versions they're trying to pitch to the German Army.

 

 

 

You need to stop this nonsense and start contributing. Nearly every relevant thing you said is incorrect,  misconceived, or misapplied.

 

It is tiresome to have someone here who is so verbose and so erroneous at the same time. It takes a lot of time to refute it all, and we are no longer young, patient men with nothing but.

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I'm just explaining what I've been told by others elsewhere.  I'm ready and willing to learn as well.  However, if that's not desired here, I'm ready and willing to leave.

 

I've read the forum rules and requests, and I'm doing the best I can with what I know.  If that's not good enough, all you have to do say please go pound sand.

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39 minutes ago, BarnOwlLover said:

I'm just explaining what I've been told by others elsewhere.  I'm ready and willing to learn as well.  However, if that's not desired here, I'm ready and willing to leave.

 

I've read the forum rules and requests, and I'm doing the best I can with what I know.  If that's not good enough, all you have to do say please go pound sand.

 

Ok, if you're honestly interested in learning, try talking less authoritatively. Asking questions is fine. As an example: 

15 hours ago, BarnOwlLover said:

The H has an upper that's nearly an inch longer than the L variant, let alone much wider.

 

This is an authoritative statement. It's also wrong. If you say it like this, I now have to correct you. Instead, try wording it like this:

 

"Is it true that the SCAR-H's receiver is an inch longer, and wider, than a SCAR-L's?"

 

And don't just word vomit. If you're here to learn, it's at the grace of people who can answer your questions. Don't test their patience.

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15 hours ago, BarnOwlLover said:

I'm just explaining what I've been told by others elsewhere.  I'm ready and willing to learn as well.  However, if that's not desired here, I'm ready and willing to leave.

 

I've read the forum rules and requests, and I'm doing the best I can with what I know.  If that's not good enough, all you have to do say please go pound sand.



I haven't logged into your account and posted as you a long account of being sexually attracted to little boys and then banned you for it.  This would suggest that some of my anger issues have been mitigated by the regimen of powerful schedule III drugs I have been taking off-label for several months.  Congratulations on the successful outcome of this test.

The reason we're treating what you're saying as laughable and obvious nonsense is because it is.  It doesn't help that, when I very gently (by my standards) point out what's wrong with it, you just make shit up.

 

 

On 7/27/2020 at 5:52 PM, BarnOwlLover said:

The H has an upper that's nearly an inch longer than the L variant, let alone much wider. 

 

If the receiver on the H is wider, then how does this exist?  If the receiver on the H is wider then how come its bolt carrier isn't visibly wider?  

Nh1fwWP.png


That especially doesn't make sense when you consider that the SCAR bolt carrier rides on rails that are an integral part of the receiver extrusion:

QqXkkjO.png


The SCAR-L and SCAR-H have exactly the same receiver cross section.  Originally, they were going to have a common receiver.  The program later relaxed the requirement for a unified receiver, which means that the uppers aren't identical.  They are, however, very close.

But you don't need to know details of the SCAR's program history to work out that the receivers probably have the same cross section.  You just need to use your goddamned head and think about it.

 

On 7/27/2020 at 5:52 PM, BarnOwlLover said:

Also, considering that most of the caliber conversions (such as 7.62x39) have focused on the H variant, I've wondered and come to think that the L is optimized around 5.56mm.  I actually can't remember there being any caliber conversions offered for the SCAR 16 aside from .300 Blackout. 



What.  Why would you think this.  Do you even think?

For one thing, caliber conversions for the SCAR-L for 7.62x39 do exist.

For another thing, this entire tangent of nonsense is internally inconsistent with the other nonsense you posted already.  If the HK 433 can accept larger calibers simply by having a magazine well that's a few pixels longer, then why does the FN SCAR require a receiver that's both wider and longer?

Like, think about this for just a fraction of a second.  Your entire train(wreck) of thought is just plain stupid.  This is what I was trying to hint at with the picture comparing the SCAR-L and SCAR-H, but this point went whistling harmlessly far, far above your head.

1)  The distance between the trunnion and the rear of the magazine well isn't what determines the maximum cartridge overall length a rifle can handle for several reasons.  The rifle needs enough distance from the inside of the rear of the magazine to the breech of the barrel plus distance to cam the locking mechanism into engagement and/or ramp the round up into alignment with the bore.  The breech of the barrel doesn't necessarily coincide with the trunnion.  Indeed, it could be argued that the FN SCAR doesn't really have a trunnion at all:

 

NbCcDs1.png

See?  There's no big internal buttress that the barrel attaches to.  It's held in from the side by screws.

2)  The thing you think is a trunnion isn't.  If you actually look at the patent, you can see that the thing you marked is the crosspin attachment for the lower portion of the handguard and the lower receiver.  It is not what holds the barrel on.

mgBUyzU.png 

 

 

ekyDbMF.png

It happens to be near the barrel mounting hardware, but it does not hold the barrel on nor does it mark the breech of the barrel, which is several millimetres further back.

3) The lower receiver is clearly intended to take 5.56x45mm COAL rounds and magazines.  If they were intending to fire 7.62x51mm from that rifle... they would put a new lower receiver on it that can take the appropriate magazines.

4)  Again, I was gently hinting at this, but you missed it, the SCAR-H has a larger ejection port to accommodate the larger cases and a longer charging handle slot to accommodate the larger stroke of the bolt carrier.  If the 433 were designed with the option of longer calibers in mind, we would also see those features, but we don't so it isn't.


Actually think next time in order to prevent yourself from posting long and tiresome nonsense.

 

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Yeah, another thing to think about is that for arcane reasons I won't explain here, the total receiver length of a gas operated, rotary-locked rifle will be equivalent to 3*(C2-C1)+R1, where C1 is the cartridge overall length of the identical pattern smaller rifle, C2 is the new COAL, and R1 is the original receiver length. So, the HK433 being obviously designed for 5.56mm, you would need more extensive modifications (new upper + lower) to accommodate 7.62.

 

What is in contention is whether a 7.62 HK433 would need a new pin axis distance, or not. I could go either way on that.

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Hey Sturgeon, you can't just drop an authoritative statement like that formula and not back it up. Please show us how you came to the number three. I'm genuinely curious. Having this extremely specialized hobby as well, I have a notepad at home with calculations made to the same end. Writing from on top of the loo at the office, I would have guessed at 2 rather than 3. Also, you must need a lot of premises to be valid for it to be true, mainly that the receiver was designed for optimization with regards to overall length.

 

There are a lot of CAD models of the scar availible online. Check out grabcad. I've got a model on my home pc that is quite accurate, and I think I got it from there. Way easier to measure than counting pixels.

 

Finally, while I enjoy the high level posting on this forum, I think you're being quite harsh on the OP. Who cares if it's the trunnion or the barrel extension.

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I haven't done the extensive modelling Sturgeon has, but, to a reasonable first approximation:

 

-Most new rifles these days are multi-lug, rotary bolt types

-There's a practical limit on how many lugs the bolt's locking area can be divided into

-There's a practical limit on how steep the cam track can be before the action of locking the bolt makes too much friction

-Therefore there is a practical limit on how much the length needed for the bolt carrier to lock and unlock the bolt can be minimized

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On 8/31/2020 at 4:17 AM, Miroslav said:

Hey Sturgeon, you can't just drop an authoritative statement like that formula and not back it up. Please show us how you came to the number three. I'm genuinely curious.

 

Well it's obvious that your receiver needs to be longer by 1 increment to accommodate the longer round. The second increment is the additional receiver length you need to accommodate the bolt which needs to not only be longer by that same 1 increment but also to travel behind the magazine enough to clear the rounds. So that's another increment. Your spring assembly and various other hardware also needs to be longer. Your bolt needs to be bigger and it will extend further too, so that's an additional bit of length, and you can approximate that as an extra increment. Together, that adds up to a 3x modifier. Take it from someone who's designed six rifles lol.
 

On 8/31/2020 at 4:17 AM, Miroslav said:

Also, you must need a lot of premises to be valid for it to be true, mainly that the receiver was designed for optimization with regards to overall length.


My formula clearly does not apply if you're pulling crazy BS. The Kel-Tec RDB does not follow this formula, for example. The F-7 doesn't follow this formula. They've both pulled tricks to cheat the length, which is ok! But most people aren't working on that level of detail so the rule applies in most circumstances.

I mean for example if your gun uses a vertically sliding breechblock and telescoped rammer assembly, then what I just said doesn't shake out. But if you're comparing an AR-15 to an AR-10, it does.

 

On 8/31/2020 at 4:17 AM, Miroslav said:

 

There are a lot of CAD models of the scar availible online. Check out grabcad. I've got a model on my home pc that is quite accurate, and I think I got it from there. Way easier to measure than counting pixels.


You know the F-4 was uploaded to GrabCAD for several months, right? I actually need to reupload it, since the ITAR rules changed.

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On 9/4/2020 at 5:45 AM, Sturgeon said:

 

[...] Your spring assembly and various other hardware also needs to be longer. Your bolt needs to be bigger and it will extend further too, so that's an additional bit of length, and you can approximate that as an extra increment. Together, that adds up to a 3x modifier. Take it from someone who's designed six rifles lol.
[...]

I could buy the first two increments, but I don't think you should count having the spring in the forend as "crazy BS", and if it's in the forend (or there's just enough space in the carrier to stuff it in there anyway) you don't have to extend the receiver to fit the spring. Also you counted the bolt length twice. And you could have the hammer extend over the rear end of the magazine (or any bolt hold open device), which would save you from having to extend the firing pin all the way from the chamber to behind the rear of the magazine. I think the SU-16 has that configuration, but I'm not sure.

Yeah ok I'll quit the semantical nitpicking. I appreciate the attempt at generalizing. I wonder how well this stacks against the HK roller locked series, or a comparison of Garand/M14/Mini 14.

 

I've got some CAD models of long guns as well, but I'll keep them to myself for now. I have a PCC design that wouldn't require all that much of a workshop to put together, compared to a locked rotating bolt, gas operated rifle.

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57 minutes ago, Miroslav said:

I could buy the first two increments, but I don't think you should count having the spring in the forend as "crazy BS", and if it's in the forend (or there's just enough space in the carrier to stuff it in there anyway) you don't have to extend the receiver to fit the spring.

 

What I said was misleading, sorry. All of my rifle designs collapse the spring into the bolt carrier and there is no length behind the bolt at full rearward extension where the spring lives. 
 

58 minutes ago, Miroslav said:

Also you counted the bolt length twice.


No, I did not. Bolt assembly and bolt are not the same thing. I'm talking about two separate properties, that of the bolt carrier length needed and that of the bolt extension during unlocking.
 

1 hour ago, Miroslav said:

And you could have the hammer extend over the rear end of the magazine (or any bolt hold open device), which would save you from having to extend the firing pin all the way from the chamber to behind the rear of the magazine. I think the SU-16 has that configuration, but I'm not sure.


The F-5 does this. It still follows this rule.

 

1 hour ago, Miroslav said:


Yeah ok I'll quit the semantical nitpicking. I appreciate the attempt at generalizing. I wonder how well this stacks against the HK roller locked series, or a comparison of Garand/M14/Mini 14.

 

I think you just didn't understand what I was saying, which is largely my fault. I said a lot of things in a confusing way because I didn't pay enough attention to my composition when I made my reply.

 

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1 hour ago, Miroslav said:

I could buy the first two increments, but I don't think you should count having the spring in the forend as "crazy BS", and if it's in the forend (or there's just enough space in the carrier to stuff it in there anyway) you don't have to extend the receiver to fit the spring. Also you counted the bolt length twice. And you could have the hammer extend over the rear end of the magazine (or any bolt hold open device), which would save you from having to extend the firing pin all the way from the chamber to behind the rear of the magazine. I think the SU-16 has that configuration, but I'm not sure.

Yeah ok I'll quit the semantical nitpicking. I appreciate the attempt at generalizing. I wonder how well this stacks against the HK roller locked series, or a comparison of Garand/M14/Mini 14.

 

I've got some CAD models of long guns as well, but I'll keep them to myself for now. I have a PCC design that wouldn't require all that much of a workshop to put together, compared to a locked rotating bolt, gas operated rifle.


You can see how the F-5 takes great pains to telescope the hammer above the magazine:

b7BXMjU.png

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@Miroslav here's an example of what I'm talking about:

0SLLmHI.png

Archangel bolt group top, compared to Bearcat (new project) bottom. Note that because the magazine well is 0.4" shorter on Bearcat, that the BCG is 0.4" shorter, and that means an additional 0.4" less receiver is required behind the magazine well. Total length savings just accounting for those two items is therefore 2x 0.4" (0.8"). Other factors included would bring the total closer to 3x.

In Bearcat's case, total savings is likely to be closer to 2.5x, because there is no difference in bolt extension distance between it and Archangel. Under normal circumstances, there would be. Also I do not have a charging handle assembly that requires a slot in the receiver or anything like that, so there's unlikely to be savings there. But you can see how a difference in cartridge OAL actually compounds the difference in receiver length just by this example.

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Well, as long as you have a set of premises to keep your definition of "normal circumstances", your formula holds up very well as a general pointer. I still think the factor "3" is high.

 

There are so many different kinds of tried and tested receiver shortening "crazy BS" design elements availible to a designer that perhaps the formula could be further specified to:

 

If: R2>3*(C2-C1)+R1

Then: designer is lazy

 

What do you mean by bolt extension distance? I'm guessing the difference in how far the bolt lugs protrude from the bolt carrier as the bolt is unlocked.

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7 hours ago, Miroslav said:

Well, as long as you have a set of premises to keep your definition of "normal circumstances", your formula holds up very well as a general pointer. I still think the factor "3" is high.


It is high but most engineers are not very good.
 

7 hours ago, Miroslav said:

 

There are so many different kinds of tried and tested receiver shortening "crazy BS" design elements availible to a designer that perhaps the formula could be further specified to:


Believe me, as the designer of the F-7 Shinden, I am no stranger to these.
 

7 hours ago, Miroslav said:

If: R2>3*(C2-C1)+R1

Then: designer is lazy


To a certain extent, yes! Or, he's very conservative, perhaps. But this is a formula for people who are not designing their own guns, but still want to make these sorts of assumptions.
 

7 hours ago, Miroslav said:

 

What do you mean by bolt extension distance? I'm guessing the difference in how far the bolt lugs protrude from the bolt carrier as the bolt is unlocked.


Distance between bolt locked and bolt unlocked positions.

For the record, I just finished the F-8 Bearcat, which is a shortened version of the F-12 Archangel, and the ratio it ended up with was 1.925:1. However, Bearcat is not a scaled down Archangel, but more of an "Archangel that ran headfirst into a wall". So it retains the same bolt extension, bolt thrust parameters, etc.

You can see them compared here:

lEYi2o2.png

aAUrabO.png

pdvjEij.png

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      Answer:  I'm saying the EM-2 was a bad design because it was a bad design.  Same as British tanks, really.  You lot design decent airplanes, but please leave the tanks, rifles and dentistry to the global superpower across the pond that owns you body and soul.  Oh, and leave cars to the Japanese.  To be honest, Americans can't do those right either.
       
      No, I'm not going to launch into some stupid tirade about how all bullpup assault rifle designs are inherently a poor idea.  I would agree with the statement that all such designs have so far been poorly executed, but frankly, very few assault rifles that aren't the AR-15 or AK are worth a damn, so that's hardly surprising.  In fact, the length savings that a bullpup design provides are very attractive provided that the designer takes the ergonomic challenges into consideration (and this the EM-2 designers did, with some unique solutions).
       
      Actually, there were two problems with the EM-2, and neither had anything to do with being a bullpup.  The first problem is that it didn't fucking work, and the second problem is that there was absolutely no way the EM-2 could have been mass-produced without completely re-thinking the design.
       
      See this test record for exhaustive documentation of the fact that the EM-2 did not work.  Points of note:
       
      -In less than ten thousand rounds the headspace of two of the EM-2s increased by .009 and .012 inches.  That is an order of magnitude larger than what is usually considered safe tolerances for headspace.
       
      -The EM-2 was less reliable than an M1 Garand.  Note that, contrary to popular assertion, the EM-2 was not particularly reliable in dust.  It was just less unreliable in dust than the other two designs, and that all three were less reliable than an M1 Garand.
       
      -The EM-2 was shockingly inaccurate with the ammunition provided and shot 14 MOA at 100 yards.  Seriously, look it up, that's what the test says.  There are clapped-out AKs buried for years in the Laotian jungle that shoot better than that.
       
      -The EM-2 had more parts breakages than any other rifle tested.
       
      -The EM-2 had more parts than any other rifle tested.
       
      -The fact that the EM-2 had a high bolt carrier velocity and problems with light primer strikes in full auto suggests it was suffering from bolt carrier bounce.
       
       
      As for the gun being completely un-suited to mass production, watch this video:
       
       
       
      Question Two:  But the EM-2 could have been developed into a good weapon system if the meanie-head Yanks hadn't insisted on the 7.62x51mm cartridge, which was too large and powerful for the EM-2 to handle!
       
      Anyone who repeats this one is ignorant of how bolt thrust works, and has done zero research on the EM-2.  In other words, anyone who says this is stupid and should feel bad for being stupid.  The maximum force exerted on the bolt of a firearm is the peak pressure multiplied by the interior area of the cartridge case.  You know, like you'd expect given the dimensional identities of force, area and pressure, if you were the sort of person who could do basic dimensional analysis, i.e. not a stupid one.
       
      Later version of the British 7mm cartridge had the same case head diameter as the 7.62x51mm NATO, so converting the design to fire the larger ammunition was not only possible but was actually done.  In fact, most the EM-2s made were in 7.62x51mm.  It was even possible to chamber the EM-2 in .30-06.
       
      I'm not going to say that this was because the basic action was strong enough to handle the 7x43mm, and therefore also strong enough to handle the 7.62x51mm NATO, because the headspace problems encountered in the 1950 test show that it really wasn't up to snuff with the weaker ammunition.  But I think it's fair to say that the EM-2 was roughly equally as capable of bashing itself to pieces in 7mm, 7.62 NATO or .30-06 flavor.
       
       
      Question Three:  You're being mean and intentionally provocative.  Didn't you say that there were some good things about the design?
       
      I did imply that there were some good aspects of the design, but I was lying.  Actually, there's only one good idea in the entire design.  But it's a really good idea, and I'm actually surprised that nobody has copied it.
       
      If you look at the patent, you can see that the magazine catch is extremely complicated.  However, per the US Army test report the magazine and magazine catch design were robust and reliable.
       
      What makes the EM-2 special is how the bolt behaves during a reload.  Like many rifles, the EM-2 has a tab on the magazine follower that pushes up the bolt catch in the receiver.  This locks the bolt open after the last shot, which helps to inform the soldier that the rifle is empty.  This part is nothing special; AR-15s, SKSs, FALs and many other rifles do this.
       
      What is special is what happens when a fresh magazine is inserted.  There is an additional lever in each magazine that is pushed by the magazine follower when the follower is in the top position of the magazine.  This lever will trip the bolt catch of the rifle provided that the follower is not in the top position; i.e. if the magazine has any ammunition in it.
       
      This means that the reload drill for an EM-2 is to fire the rifle until it is empty and the bolt locks back, then pull out the empty magazine, and put in a fresh one.  That's it; no fussing with the charging handle, no hitting a bolt release.  When the first magazine runs empty the bolt gets locked open, and as soon as a loaded one is inserted the bolt closes itself again.  This is a very good solution to the problem of fast reloads in a bullpup (or any other firearm).  It's so clever that I'm actually surprised that nobody has copied it.
       
      Question Four:  But what about the intermediate cartridge the EM-2 fired?  Doesn't that represent a lost opportunity vis a vis the too powerful 7.62 NATO?
       
      Sort of, but not really.  The 7mm ammunition the EM-2 fired went through several iterations, becoming increasingly powerful.  The earliest versions of the 7mm ammunition had similar ballistics to Soviet 7.62x39mm, while the last versions were only a hair less powerful than 7.62x51mm NATO.
       
      As for the 7mm ammunition having some optimum balance between weight, recoil and trajectory, I'm skeptical.  The bullets the 7mm cartridges used were not particularly aerodynamic, so while they enjoyed good sectional density and (in the earlier stages) moderate recoil, it's not like they were getting everything they could have out of the design.
       

      note the flat base
       
      In addition, the .280 ammunition was miserably inaccurate.  Check the US rifle tests; the .280 chambered proto-FAL couldn't hit anything either.
    • By Collimatrix
      At the end of January, 2018 and after many false starts, the Russian military formally announced the limited adoption of the AEK-971 and AEK-973 rifles.  These rifles feature an unusual counterbalanced breech mechanism which is intended to improve handling, especially during full auto fire.  While exotic outside of Russia, these counter-balanced rifles are not at all new.  In fact, the 2018 adoption of the AEK-971 represents the first success of a rifle concept that has been around for a some time.

      Earliest Origins


      Animated diagram of the AK-107/108
       
      Balanced action recoil systems (BARS) work by accelerating a mass in the opposite direction of the bolt carrier.  The countermass is of similar mass to the bolt carrier and synchronized to move in the opposite direction by a rack and pinion.  This cancels out some, but not all of the impulses associated with self-loading actions.  But more on that later.

      Long before Soviet small arms engineers began experimenting with BARS, a number of production weapons featured synchronized masses moving in opposite directions.  Generally speaking, any stabilization that these actions provided was an incidental benefit.  Rather, these designs were either attempts to get around patents, or very early developments in the history of autoloading weapons when the design best practices had not been standardized yet.  These designs featured a forward-moving gas trap that, of necessity, needed its motion converted into rearward motion by either a lever or rack and pinion.
       

      The French St. Etienne Machine Gun
       

      The Danish Bang rifle
       
      At around the same time, inventors started toying with the idea of using synchronized counter-masses deliberately to cancel out recoil impulses.  The earliest patent for such a design comes from 1908 from obscure firearms designer Ludwig Mertens:


       
      More information on these early developments is in this article on the matter by Max Popenker.
       
      Soviet designers began investigating the BARS concept in earnest in the early 1970s.  This is worth noting; these early BARS rifles were actually trialed against the AK-74.
       

      The AL-7 rifle, a BARS rifle from the early 1970s
       
      The Soviet military chose the more mechanically orthodox AK-74 as a stopgap measure in order to get a small-caliber, high-velocity rifle to the front lines as quickly as possible.  Of course, the thing about stopgap weapons is that they always end up hanging around longer than intended, and forty four years later Russian troops are still equipped with the AK-74.

      A small number of submachine gun prototypes with a BARS-like system were trialed, but not mass-produced.  The gas operated action of a rifle can be balanced with a fairly small synchronizer rack and pinion, but the blowback action of a submachine gun requires a fairly large and massive synchronizer gear or lever.  This is because in a gas operated rifle a second gas piston can be attached to the countermass, thereby unloading the synchronizer gear.

      There are three BARS designs of note from Russia:

      AK-107/AK-108
       


      The AK-107 and AK-108 are BARS rifles in 5.45x39mm and 5.56x45mm respectively.  These rifles are products of the Kalashnikov design bureau and Izmash factory, now Kalashnikov Concern.  Internally they are very similar to an AK, only with the countermass and synchronizer unit situated above the bolt carrier group.


       

      Close up of synchronizer and dual return spring assemblies

      This is configuration is almost identical to the AL-7 design of the early 1970s.  Like the more conventional AK-100 series, the AK-107/AK-108 were offered for export during the late 1990s and early 2000s, but they failed to attract any customers.  The furniture is very similar to the AK-100 series, and indeed the only obvious external difference is the long tube protruding from the gas block and bridging the gap to the front sight.
       
      The AK-107 has re-emerged recently as the Saiga 107, a rifle clearly intended for competitive shooting events like 3-gun.
       

       
      AEK-971

      The rival Kovrov design bureau was only slightly behind the Kalashnikov design bureau in exploring the BARS concept.  Their earliest prototype featuring the system, the SA-006 (also transliterated as CA-006) also dates from the early 1970s.



      Chief designer Sergey Koksharov refined this design into the AEK-971.  The chief refinement of his design over the first-generation balanced action prototypes from the early 1970s is that the countermass sits inside the bolt carrier, rather than being stacked on top of it.  This is a more compact installation of the mechanism, but otherwise accomplishes the same thing.


       

      Moving parts group of the AEK-971

      The early AEK-971 had a triangular metal buttstock and a Kalashnikov-style safety lever on the right side of the rifle.



      In this guise the rifle competed unsuccessfully with Nikonov's AN-94 design in the Abakan competition.  Considering that a relative handful of AN-94s were ever produced, this was perhaps not a terrible loss for the Kovrov design bureau.

      After the end of the Soviet Union, the AEK-971 design was picked up by the Degtyarev factory, itself a division of the state-owned Rostec.



      The Degtyarev factory would unsuccessfully try to make sales of the weapon for the next twenty four years.  In the meantime, they made some small refinements to the rifle.  The Kalashnikov-style safety lever was deleted and replaced with a thumb safety on the left side of the receiver.


       
      Later on the Degtyarev factory caught HK fever, and a very HK-esque sliding metal stock was added in addition to a very HK-esque rear sight.  The thumb safety lever was also made ambidextrous.  The handguard was changed a few times.



      Still, reception to the rifle was lukewarm.  The 2018 announcement that the rifle would be procured in limited numbers alongside more conventional AK rifles is not exactly a coup.  The numbers bought are likely to be very low.  A 5.56mm AEK-972 and 7.62x39mm AEK-973 also exist.  The newest version of the rifle has been referred to as A-545.

      AKB and AKB-1


      AKB-1


      AKB


      AKB, closeup of the receiver

      The AKB and AKB-1 are a pair of painfully obscure designs designed by Viktor Kalashnikov, Mikhail Kalashnikov's son.  The later AKB-1 is the more conservative of the two, while the AKB is quite wild.

      Both rifles use a more or less conventional AK type bolt carrier, but the AKB uses the barrel as the countermass.  That's right; the entire barrel shoots forward while the bolt carrier moves back!  This unusual arrangement also allowed for an extremely high cyclic rate of fire; 2000RPM.  Later on a burst limiter and rate of fire limiter were added.  The rifle would fire at the full 2000 RPM for two round bursts, but a mere 1000 RPM for full auto.

      The AKB-1 was a far more conventional design, but it still had a BARS.  In this design the countermass was nested inside the main bolt carrier, similar to the AEK-971.

      Not a great deal of information is available about these rifles, but @Hrachya H wrote an article on them which can be read here.
       
       
    • By Sturgeon
      As a current side project stops and starts according to my whims, I figured I might as well create here and keep updated a list of rules/guidelines for design of lightweight automatic/autoloading rifles and other weapons. Here's what I have so far:

      1. Volume is mass; smaller means lighter.
       
      2. The lightest, strongest shape is the sphere, and it has the least surface area for its volume. Cubes, though conceptually simple, should be avoided where possible. All light weapons desire to approach the shape of the cylinder, an elongate sphere.

      3. (For conventional-layout weapons) Adding one ounce of weight in front of the point of balance adds two in total.

      4. The primary mass is the primary driver of the total system mass. As a rule of thumb, adding 1 gram to the bolt mass adds 10 grams total to the rifle.

      5. The only way to achieve exceptional lightness of weight is to reduce weight wherever possible, no matter how minor the savings in each case. The best way to lighten a rifle by 10% is not by cutting the weight of one component dramatically, but by reducing the weight of all components by 10%.
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