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Trident Arms AR9 Short Barrel Rifle SBR Project


This is a review of my Custom Built dedicated 9mm AR-9 Short Barrel Rifle (SBR) project.  I based this build on a dedicated 9mm AR lower. This lower receiver is dedicated to the 9mm cartridge and does not require a magazine adapter block.

Unlike other 9mm options, this lower is machined to look appropriate for the Colt pattern 9mm magazine.  This AR-15 billet 9mm caliber lower is designed to have the same lines as an AR-15 upper and can also be ordered as a Vltor matching.  The feed ramp and ejector are nitride coated to provide smooth operation and easy cleaning.
Material:           T1 or T2 billet
Fabrication:      CNC machined
Coating:            Type III Hard Coat Black Anodize
Features:           Upper Receiver tensioning screw; Nitride feed ramp and ejector

"This will be a dedicated 9mm SBR once completed".
Custom Built dedicated 9mm AR-9 Short Barrel Rifle (SBR) Project
I decided to get the Vltor matching lower since the lines would match several uppers that I was considering. I ordered my lower and after a slight mix-up and several months wait, finally got it. 

The first thing I did was to completely inspect it.  I found no flaws and excellent machining and workmanship.  The lower arrived with the nitride feed ramp and ejector installed. The engraving was crisp, easy to read and the coating is even.  "This is a quality lower".
stripped AR-9 lower
Now that I had my lower, I quickly completed the Form 1 to get it registered as an SBR.  I had already received my approval on my Form 4 (and paid the $200 tax stamp) for the suppressor.  After another 4 months wait (and another $200 tax stamp), I received my Form 1 approval from BATF and was ready to get my build started. 

I now needed to define by project build goals. I wanted an AR that was affordable to shoot and I want to keep it as short as possible enough for close quarters without sacrificing any long range capabilities that it could have.

There are a couple of ways to achieve this: I could shorten the barrel or I could shorten the butt stock.  I figured I would do both.  First, I installed a standard AR-15 DPMS lower parts kit (mostly, as I didn’t use the trigger or the grip), a 3lb Timney Trigger w/KNS Antiwalk Pins (a must have on any AR) and a Falcon Industries Black Ergo Sure Grip.
I grabbed a milspec buffer tube off the shelf and began reducing the thread length by approx 3/4”.  I rethreaded the tube and re-blued it and then installed it on the lower.  I added a .308 buffer and spring and verified my clearances.  The .308 buffer would work great and I still had room if I needed to reduce it any further.
I did a little painting with a toothpick and filled in the engraving with some color.  I use enamel paint. It works best to let it sit for an hour and then simply wipe off the excess with some mineral spirits.
Once you wipe the excess off, let it sit overnight or you will have a mess on your hands.  And remember; if in doubt, tape it off!!! This will save allot of clean up and frustration.  Once it's dry, you can then wipe it down with a silicone rag.In retrospect, I should have used a fill stick, but this is what I had on hand at the time.
I used a Vltor Modstock and shortened it by 2 1/2” giving me a 4 1/2” collapsible buttstock for a true SBR and reduced my overall length to 25” with the suppressor installed.  Not to mention, it looks way cool and is very functional.  I installed my modified modstock with a nice piece of tube foam that I added for comfort and to keep my cheek off the buffer tube.  This completed my lower.
For the upper receiver, I had considered the Vltor MUR, or Gemtech's Talon upper, but ended up using a Spikes Tactical dedicated 9mm billet flat top.  I didn’t want to sacrifice any long range performance so I installed a 5" threaded Green Mountain barrel.   This will provide a longer barrel while still maintaining my overall length goal.
I decided to use a Gemtech Multimount 9mm suppressor to keep it interchangeable with my 9mm pistols.  This required using Gemtech’s Threaded Multimount Endcap Adaptor.  I used Threadlocker and secured this to my barrel.  I didn’t want the suppressor endcap un-screwing when I removed my suppressor.

Next I used a Troy Industries 9” TRX Extreme Rail and discovered that my suppressor and adaptor wouldn’t completely fit into the tube.  Apparently, Troy doesn’t completely machine the inside of the tube.

So, it was back to the work bench for a little modification.  I grabbed a cylindrical sanding drum and I bored the crap out of
the tube and after a little work and some refinishing it was able to accept the suppressor and adaptor.  I installed a lower rail and then added a GG&G vertical forward grip. This completed the front tube assembly.
Now I needed to add some optics.  For my back-up sights, I installed a pair of Troy Industries BUIS Folding Battle Sighs and then added a 2MOA Aimpoint Comp M3 with a Cantilever Mounting Base.

I installed a CMMG 9mm BCG and then mounted my upper to the lower to complete my build.
After a function check and some minor adjusting to the tensioning screw (every AR should have one of these!!!), it was a perfect marriage.  The lines match exactly and there is no slop between the upper and lower. This thing is really looking sick!!!
Now that my build was complete, I was itching to get it out to the range and test it.  I ran several hundred rounds through it and it performed and functioned flawlessly.  Very little recoil was felt making it easy to remain on target.  The magazine well accepted the colt pattern magazines without incident.
I tried several different loads and it loved them all, even my reloads.  I even fed it some 147gr FMJ subsonic loads throught it.  The bolt cycled really well with the subsonic loads.  This thing is not much louder than a pellet gun.  You still get the downrange sonic crack of the bullet, but the sound levels at the gun are extremely reduced as it was just stupid quiet; all that you really heard is a little "crack" from the muzzle and the "ka-thump" of the bolt cycling.  I have to say that I definitely achieved my project goals on this build and one that is just plain fun to shoot.  The short barrel makes for a lightweight and very maneuverable package, without suffering the drastic reduction in ballistic effectiveness that would be seen with a typical AR-15 of the same size.
Custom AR-9 Suppressed SBR
The only noticeable drawback was excessive gas escaping at the charging handle.  This will be easily overcome with the installation of a PRI Gas Buster Charging Handle w/ Combat Latch.

It is really nice to be able to sling an affordable round downrange on an AR platform.  Now I can get some AR trigger time in at my local indoor range without having to take out a loan for ammo.  This is one gun that drew a lot of attention from the other shooters at the range and definitely produced the "cool guy factor"...   All in all, this is truly a sweet setup and a nice addition to my collection.
Custom dedicated 9mm AR-9 with a suppressed Vltor upper
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