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Rainier Arms, LLC

Rainier Arms UltraMatch Billet Ambi Lower Receiver MOD 3

Rainier Arms UltraMatch Billet Ambi Lower Receiver MOD 3
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Availability: Out of stock




Rainier Arms UltraMatch Billet Lower Receiver

Our billet sets are CNC machined from solid billet 7075-T6 aluminum which is 70% stronger than the commonly used 6061 aluminum and finished with milspec hardcoat anodize to a surface hardness of 60 Rockwell. We have designed our lowers with an ambidextrous mag release and bolt release with extended latch for smoother deployment. The precision machining on our billets lowers will line up perfectly to our Rainier Arms UltraMatch Billet Upper Receiver or any other billet uppers out there.


  • Ambidextrous Extended Bolt Release
  • Ambidextrous Magazine Release
  • 7075 Billet Aluminum
  • Flared Magwell
  • Integrated Trigger Guard
  • Tensioning Screw for proper Upper/Lower Fit
  • Compatible with 45° safety selector levers

FFL Required Before Shipping.

Please have your dealer email their license to or they can also fax it in. Please give us a few days to process the information.

Additional Info

Additional Info

Manufacturer Rainier Arms, LLC
Finish No
Barrel Length No
Caliber No
Configuration No
Option No
Gas Length No
Height No
Rail Length No
Mount No
Profile No
Reticle No
Co Witness No
Size No


Customer Reviews (14)

High QualityReview by Richard
I matched it with a GIBBZ Upper and it fit flawlessly.
It's not documented but it comes with:
Bolt Catch Plunger
Bolt Catch Roll Pin (Actually a screw)

So you don't need to buy those things.
The Bolt Catch Roll Pin and the Magazine Release Roll Pins are actually screws which I thought was easier to install / use.

Side Note:
Does NOT fit Beta C Mags! The flared magazine well is too large to allow the magazine to click in. Some grinding would be required.

Overall I'm very happy with it. (Posted on 12/1/2016)
No commentReview by kevin
- (Posted on 11/12/2016)
Fit and finish look great!Review by Michael
Fit and finish is great. The only thing to be aware of is that the spring for the rear take down pin installs from below under a set screw. If you have a normal length spring then you will have to cut some coils. (Posted on 10/26/2016)
Design and build Review by Robert
Rainier mod 3 lower finish and fit are amazing,the fit to cmt uppers are snug and match up perfect,it does go together to make a left handed ar15 both mod 3 and cmt left hand upper (Posted on 10/9/2016)
AwesomeReview by Dustin
This lower is awesome! The fit and feel are top notch. Dont forget to put loc-tite on all the little set screws they WILL back out. This is perfect for leftys such as myself. I can use my left index finger to fire, drop a mag and my right thumb to drop the bolt carrier while changing mags. I love it. Super fast shipping and great customer service from Rainier. Will be doing more business in the future. (Posted on 9/25/2016)
No commentReview by Michael
- (Posted on 9/24/2016)
No commentReview by John
This lower is exactly what I was looking for. No milling or cutting residue/excess. All parts fit together forst try. No upper/lower rattle. I will definitely come to Rainier for my next build. (Posted on 8/5/2016)
Excellent, Will buy more soon!Review by Justin
It's may seem expensive, but 1. Not really expensive compared to other billet receivers. 2.worth every penny because of the fit and finish is IMO second to none including a Spikes tactical set I bought that cost nearly twice as much.

I love it, and will build another on this lower soon. (Posted on 7/28/2016)
compatibility Review by Patrick
Very nice lower!

Had some fitment issues with certain KNS anti-roll pin kits hitting the raised machining for the ambi bolt release button. Go small if you are going to use roll pins.

Also, when fully collapsed, the right side guide rod on my Maxim CQB stock comes in contact with the ambi bolt release button. I have to depress it and slide the rod over the recessed button to completely collapse.

In all, I expected to exchange functionality in areas with buying an ambi lower, so it evenly trades out for me.

(Posted on 7/15/2016)
No commentReview by Cong
- (Posted on 7/14/2016)
Can't wait!Review by Brian
So I originally ordered the basic Rainier Arms lower to be my very first AR build, but after doing a bit more research I decided to go with this one since I'm left handed and was gonna spend a fair amount of money on ambi parts so I called Rainier to change my order, the guy on the phone was nice enough to go in the back and halt my delivery to have it swapped out. I can't wait to recieve this product! Will review again when I get it, just giving 2 thumbs up on their customer service. (Posted on 7/8/2016)
No commentReview by Jared
- (Posted on 7/5/2016)
No commentReview by Scott
Pros: Looks/feels great; Ambi mag & bolt release controls work very well; Threaded dowel pins in place of roll pins work well and are a great improvement; Set-screws behind detent springs are a smart idea to hold them in place without risk of them going flying.

Cons: Price - premium price for premium product. But >$200 is a hard pill to swallow for one lower when standard forged lowers can be had for ~$50; Bolt catch release button works only one-way - it will release the bolt if it's locked to the rear, but will not catch the bolt if pressed while the bolt is brought back. You will still have to use the left-side control to lock back the bolt without an empty mag in the gun. I knew this when I bought the lower but thought it was an important distinction for those who may not realize it. (Posted on 5/28/2016)
No commentReview by Nick
I've been impressed on how the ambi controls function. This is the best lower that I have used. (Posted on 5/25/2016)

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