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Sturgeon's House

The Small Arms Thread, Part 8: 2018; ICSR to be replaced by US Army with interim 15mm Revolver Cannon.


Khand-e

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The most interesting guns at Range Day were bolts and revolvers. FML.

I could lend you my '05 Ross, then every time you load it, people could place bets about "the bolt blowing out" or similar bullshit.

The "Controlled Platform " is rather slick to play with, I have to say.

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Since Tracking Point seems to be back in the news; does anyone care to bet when shooting over open sights or using passive optics will become a historical sport like black powder or archery?

I know that the former is on the way there already, so my bet is 20 years.

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Since Tracking Point seems to be back in the news; does anyone care to bet when shooting over open sights or using passive optics will become a historical sport like black powder or archery?

I know that the former is on the way there already, so my bet is 20 years.

Outside of hunting, iron sights are already there.

Actively stabilized optics are probably gonna be just as slow in coming as passive glass was.

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I'm curious about the Steyr STM-556 and the Rheinmetall/Steyr RS-556.  Supposedly the latter is a variant of the former, but on closer inspection I'm not so sure.

 

u2Q38Bz.png

 

This is the STM-556.  Supposedly it's an AUG repackaged into an AR-15 shaped rifle.

 

Circled in blue are the series of interrupted lugs that lock the barrel to the barrel extension.  In most AR-15 based designs with a quick-change barrel, each barrel has its own barrel extension, which is permanently attached to the barrel.  This is the case in the MGI Hydra, for example:

 

8jHUGEz.jpg

 

However, this is not how the AUG works.  In the AUG the barrel extension stays in the receiver and the barrel locks into it by a series of interrupted lugs:

 

IoCrfFM.jpg

 

So the quick-change barrel system on the STM-556 does appear to be AUG-derived.

 

But what about the bulge on the left side of the upper receiver, circled in red?

 

AR-15s have this bulge to accommodate the rotation of the cam pin.  Most AR-15 derived-designs have this bulge; 416s have it too.  Inside the upper they have a pocket machined out to give the cam pin space to turn:

 

zCZu8sf.jpg?1

 

The straight section before this pocket is also what prevents the cam pin from turning prematurely.  It does this by simple physical interference; the cam pin just scrapes against the upper left inside margin of the receiver.  This is one of the highest-friction areas in an AR-15 and also one that loses the finish the fastest.

 

But in AUGs the cam pin does not protrude from the bolt carrier:

 

0me6Cy0.jpg

 

The rotation of the bolt is instead controlled by a toothed, sheet metal collar that locks the bolt in place until the collar is retracted by running into the barrel extension.  This is a somewhat more complicated system, but it creates less friction and less wear.

 

But the STM-556 appears to use an AR-15 style setup with a protruding cam pin, or else it wouldn't need the bulge on the left side of the receiver.

 

But look at the RS-556:

 

MyA9X9d.jpg

 

 

No bulge!

 

Does this mean that the RS-556 is different from the STM-556 and uses a more AUG-style cam pin and bolt collar?  That is one possibility.  However, there is another possibility:

 

yUcRAEg.jpg

 

This is an extruded AR-15 upper.  It also lacks the bulge.  Extruded AR-15 uppers usually lack the bulge and simply have a thicker left sidewall.  In order to accommodate the bolt catch lever, they usually have a cutout, and this cutout can be seen in the RS-556 above.  So I think that the most likely explanation for what we're seeing is that the RS-556 uses an extruded upper receiver (which would be cheaper to produce in large numbers) while the STM-556 did not.

 

However, extruded upper receivers for the AR-15 usually do not have case deflectors or forward assists, which the RS-556 clearly does have.

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Also keeping the Beretta M9 would have been the preferred of any of these options. But I guess telling the lesbian Major at Civil Affairs to man up and grow a bigger set of hands so she can manipulate the M9's controls properly wasn't an option...

 

As much as I love my 92, if they are going to replace the current inventory they might as well use a modern design.

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