Rock River Arms

rock river 16" mid-length upper receiver ar-15

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Rock River 16" Mid-Length AR-15 Complete Upper Receiver (AR0874B)

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The Rock River AR-15 upper receiver comes complete with bolt carrier group & charging handle.  This AR-15 upper will fit on any standard AR-15 lower receiver.  Once this upper is mated to a complete lower receiver, you will have a fully functioning carbine that is ready to fire.



Rock River chose a 16” barrel for this upper receiver.  16” is the shorted barrel allowed without having to go through an extensive background check per the National Firearms Act. 


The barrel has a 5.56x45mm NATO spec chamber.  This chamber dimension allows this upper receiver to fire both commercial .223 Remington ammunition, as well as military-spec 5.56x45mm ammo.


The barrel is a 1:9” twist rate.  This means that the barrel with rotate the projectile one full, 360-degree revolution for every 9” of barrel length.  This is the most common AR-15 barrel twist rate.  This twist rate will work with a variety of projectile grain weighs, from less than 50-grains to heavier than 70-grains. The most common AR-15 ammunition available on the market today is between 55-62 grains, which is perfect for the 1:9 twist barrel.


Gas System

This upper utilizes the traditional direct impingement gas system.  The barrel is set up with a mid-length gas system, which is longer than the carbine gas system, which is also commonly seen on 16” AR-15’s.  The mid-length gas system has been reported as being extremely reliable while also having a slight decrease in the perceived recoil.  Additionally, the longer mid-length gas system allows for a longer sight radius and a longer handguard.


Other Features

At the business end of the barrel, you will find a standard A2 flash hider.  This flash hider helps to control muzzle flash and also works as a compensator.  Only the top half of the muzzle device is ported.  This has two primary functions.  Since the device is only ported on top, it allows the propellant gases to escape only out of the top section of the muzzle device.  This has the effect of forcing the muzzle in a downward direction.  This can help to minimize muzzle flip, to allow for more controlled shooting.  Additionally, when firing prone or in a dusty environment, the solid bottom portion will help to minimized disturbance to the ground immediately below the muzzle, thereby avoiding kicking up a lot of dust.


This upper receiver assembly utilized a flat top receiver.  The receiver has Picatinny railing on the top section.  This allows you to choose and mount any iron sight, red dot sight, or magnified optic that you would want that has the proper Picatinny mount.


Additional Information

Part # AR0874B
Manufacturer Rock River Arms


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