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This is intended for people interested in the subject of military guns and their ammunition, with emphasis on automatic weapons, particularly in larger calibres (12.7+mm).

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Exploring The Design Space   Ammunition <20mm

Started 25/7/15 by NathanielF; 99551 views.
QuintusO

From: QuintusO

12-Sep

I confused you talking about extrusions with the 40mm CF tubing, my bad.

nincomp

From: nincomp

12-Sep

QuintusO said...

Why they felt they needed a fixed stock is beyond me. I guess just because they wanted to sell the old stockpile of unwanted GWACS lowers.

They covered this in YouTube videos several years ago when they did their initial WWSD project.  The primary goals were light weight, good balance, and durability.  The original AR15 used advanced materials for its day, so they decided to look at modern materials.   The InRange guys have quite a lot of experience in 2-gun competitions and semi-auto rifle usage and had noticed that the majority of competitors adjusted their stocks to pretty much the same length.  That is what they decided to go with.  Apparently, light weight and durability outweighed compactness.  They relate an experience where a truck accidentally backed over some rifles and the only ones not broken had polymer stocks.

The GWACS lower sold out very soon after the first WWSD project was posted in 2017.  The molds became too worn for more production runs.  Some ex-GWACS employees now work at KE Arms and decided to update the polymer receiver.  The current videos show the initial test batch made with the production tooling.

QuintusO

From: QuintusO

12-Sep

OK here's the straight dope on extrusions and why Archangel and Bearcat don't use monolithic upper receivers, because those two things are related.

An extrusion is fundamentally made in the same way that noodles are made. A material, in this case aluminum, is pushed through a die and comes out in long ropes with whatever cross section the dies dictate. Extruding aluminum is extremely cheap, and even better, unlike forging, the tooling costs are not that high. However, it does have some disadvantages. The first (1) and most obvious is that the product of the extrusion will have a constant cross-section. The second (2), and less obvious, is that the extrusions do not come out as perfect rods, but have a little bit of curvature and bend to them. A proper extrusion setup will minimize this, but cannot completely eliminate it.

(1) is an obvious disadvantage for rifles. You certainly can make a rifle that conforms to this idea, and the archetypical example is the FN SCAR. However, the SCAR has several problems as a result of this construction. The first is that it's fairly heavy, being about half a pound heavier than a like-configuration AR-15, despite having a completely polymer lower and stock assembly. The second is that the various mounting points within the SCAR's receiver are problematic. Since the extrusion is a simple U-shaped segment, the various elements within it must be (literally) bolted on. This is an issue for two reasons. First, at every bulkhead (stock mount, trunnion, etc), the material must be "double thick" to allow for structural strength and enough purchase for fasteners. Second, the fasteners can come loose, or induce enough play that the bulkheads are not as tight as you might like. The SCAR-H in particular has struggled to find purchase among the large frame precision rifle market because the necessity of the barrel being screwed in place transversely does not support it well enough to achieve very high levels of precision, such as would be desired in a DMR.

(2) is not much of an obstacle, per se, but in order to maintain tolerance across the full length of a monolithic receiver-rail high amount of precision must be maintained during the extrusion process, and the rejection rate for extrusion segments is likely to be much higher. It is therefore desirable for the cut segments to be shorter, as a greater percentage can reclaimed from a length of extrusion as segments.

To solve both of these problems, Archangel and Bearcat do not use monolithic receivers and allow for some material to be machined out of them after the extrusion is cut. The split receiver/rail design also allows for minimized material rejection during extrusion, and it allows for the extrusion shapes to be tailored specifically to the receiver and the rail, respectively. The extrusion for the Bearcat upper receiver looks like this:



The extrusion for the Bearcat/Archangel rail looks like this:



If they were to be made in one piece, it would have to look like this:

Instead of a 9" receiver segment and a 12" rail segment, you would have to get as many 21" monolithic segments out of a piece of extrusion as you could, and each continuous segment would have to be in tolerance. It's not that this is impossible (it's not, by any means), but it's easier if the segments are smaller (of course, my approach does require two separate sets of dies).

The monolithic segment would also require much more post machining, including technically complex broaching, to match the required internal contour of the Archangel/Bearcat design. Obviously, if you took this approach, you'd want to redesign the entire gun to minimize this.

The "downside" of doing this is theoretically lower rigidity between the rail and the receiver, but this is juice that is probably not worth the squeeze. It's true that a monolithic receiver would be the most rigid. LMT has shown the way on this with their monolithic forged uppers which are nearly indestructible (but quite expensive). However, monolithic receivers are all you get if you choose that route. You select a rail length and are stuck with it. If you want the equivalent of a 7" carbine rail, fine, but what if you want a 13" rail or a 15" rail or a 9" rail for your 10.5" barreled guns? You need to not only manufacture entirely new receivers for these weapons, but you also cannot easily retrofit one type into another. Perhaps you might think this was good for sales, but I don't think it makes for a good rifle. Also, without an easy way to dismount the rail, there are many things underneath it that will be very difficult to access, such as gas blocks, pistons, barrel nuts, etc. You can get around this (the SCAR, for example, does), but it comes with corresponding weight penalties. It would be impossible for me to get under 5 pounds like I have if I were to use the SCAR's method of construction (dammit, now that I've said that I'm going to have to go prove it hahaha). 

The post-SCAR noodle rifles have all learned this lesson and do not use the SCAR's method of construction. All allow for substantial post machining to the receiver, see the CZ 805 Bren 2:



(note the substantial cuts made to the extrusion to vary its cross-section)


and the HK433:



(note the large cutout in the extrusion to allow for separate rail segment. So now you need two extrusions anyway, but they need a total length of some 30 inches!)

The question is then "can we have a separate rail and receiver mated with the barrel nut, and still maintain low enough dispersion for laser attachments?" Uh, yes. We've been doing that for well over a decade. Geissele, Hodge, and others have designs that meet this requirement without issue. As sexy as "monolithic" might seem on a brochure, there's no reason to change this. My approach works, allows for the lightest possible weight through optimized geometry, minimizes the rejection rate of extrusion segments, and has less scrap than what HK and Bushmaster are doing.

  • Edited 12 September 2020 19:29  by  QuintusO
QuintusO

From: QuintusO

12-Sep

nincomp said:

They covered this in YouTube videos several years ago when they did their initial WWSD project.  The primary goals were light weight, good balance, and durability.  The original AR15 used advanced materials for its day, so they decided to look at modern materials.   The InRange guys have quite a lot of experience in 2-gun competitions and semi-auto rifle usage and had noticed that the majority of competitors adjusted their stocks to pretty much the same length.  That is what they decided to go with.  Apparently, light weight and durability outweighed compactness.  They relate an experience where a truck accidentally backed over some rifles and the only ones not broken had polymer stocks. The GWACS lower sold out very soon after the first WWSD project was posted in 2017.  The molds became too worn for more production runs.  Some ex-GWACS employees now work at KE Arms and decided to update the polymer receiver.  The current videos show the initial test batch made with the production tooling.

Oh I know what they said.

Farmplinker

From: Farmplinker

12-Sep

Hopefully it's cheaper than a Q Fix?

Red7272

From: Red7272

12-Sep

Mr. T (MrT4) said:

I haven't commented on the design past the use of the rather beefy extrusion and separate handguard. The rest of my rant is in regards to questions about the AR15 design not being the ultimate design.

AR15 is a terrible design from the mag well to the bolt handle and the prissy bolt. Tavor is as close as anyone has got to the ultimate rifle to date. 

QuintusO

From: QuintusO

12-Sep

Red7272 said:

AR15 is a terrible design from the mag well to the bolt handle and the prissy bolt. Tavor is as close as anyone has got to the ultimate rifle to date. 

This really shows what you know.

Red7272

From: Red7272

13-Sep

QuintusO said:

This really shows what you know.

I would have said the AK but everyone knows that a real man's penis will fall of if he touches a gun with the cocking handle on the right side. 

EmericD

From: EmericD

13-Sep

QuintusO said:

Have you considered that the SCAR (which is made of cheap plastic and extrusions that require almost no post machining, and which sells for about $1100 on the military market last I checked) can't compete with more expensive forged guns LMTs, Colt Canadas, and HKs, and THAT'S why it's "boutique"?

Without some paperwork error from FN Herstal, the French army would have been equipped with FN SCAR-L to replace the FAMAS...

And we bought the SCAR-H PR to replace the FRF2 precision rifle.

Mr. T (MrT4)

From: Mr. T (MrT4)

13-Sep

In regards to Bren 2 i had some insights and hands-on experience into both early pre production models and couple of months ago with ones made for French GIGN in 7.62, I dont think SCAR was of much influence, the BREN2 was initially designed to be all plastic on both upper and lower  but one of the things Manufacturers learned from G36 is that once you get the metal parts hot plastic upper doesn't aid to shed heat any time soon  hence the redesgn for an aluminum upper. 

The 2 part upper /forend no HK in addition to offering the modularity helps a bit with keeping the heat of your handguard, These all-aluminum handguards without any plastic inserts get hot,i remember one of the test sessions with short barrel BREN2 and there were 20+ of us shooting 3-4 guns, the forends became so hot that you could barrel hold the gun without gloves and we weren't even doing any full auto  

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