Our Rainier Arms Mountain Series upper receiver group was designed for the enthusiast that's looking for a solid foundation for their next upper build using our 1:7 twist Mountain series barrel, our Mil-Spec upper receiver group and Lo Profile gas block. The rest is entirely up to the customer and can be easily built out.

Barrel Specs:

Barrel Material: Chrome Moly Vanadium Steel
Made of Mil Spec M249 Machine Gun barrel steel, with heavy M249 Chrome Lining, (appx. 2 times as thick as an M4 or M16)
Barrel Type: Cold Hammer Forged
Barrel Caliber: 5.56mm NATO Barrel
Barrel Length: 14.5 Mid Gas, 16 Mid Gas, or 18 Rifle Gas
Barrel Profile: Modified Mid Weight Government Profile
Twist Rate: 1:7
Muzzle Thread: 1/2A~—28 TPI (Threads Per Inch)
Diameter At Gas Block: .750
Bore: Chrome Lined
Chamber: 5.56mm NATO

Does NOT come with a BCG, Muzzle device, Charging handle or handguard.

Component List:

Rainier Arms Mountain Mid Weight Series 1:7 Twist
Rainier Arms Match Lo Pro gas block
Rainier Arms Forged Mil-spec Upper Receiver with UPK
Rainier Arms Barrel nut
Gas tube
Weight: 18" - 2lbs 8.7 oz
Weight: 16" - 2lbs 6 oz


Price compare for RA-SURG - Of This World No. 15 Art Print Art Poster Print by Aleah Koury, 24x24

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Comments (6)

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Double chrome for that l33t range operator.

0 votes
0 votes

$300 for a stripped upper? This ain't a deal. You can get any number of assembled uppers for less.

0 votes
1 vote

The barrel is what makes this a deal. PSA had a special on some of these surplus military issue m249 barrels as well. They’re made by FN Herstal.

3 votes
0 votes

They sell these barrels for $299.99, so you are would pay at least $125 for a upper/gas system of equal quality. That brings the actual cost of the barrel to about $175, which is a hell of a deal for a barrel of this quality.

0 votes
0 votes

True dat. Chf chrome lined, your kid, and your kids kid prolly won't shoot it out.

0 votes
0 votes

...but this is from Rainer arms though. Maybe te deal is for all three in the picture?

0 votes
0 votes
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