What if ??

[Jerry R]

Disclaimer(s): I have posted this on another forum. This is not an advertisement or commercial for any company or product. I have no affiliation with any company or product mentioned in this thread. All components were purchased at retail or advertised pricing. Selections made for the build were based solely on personal whim or perceived requirement for the build. Now, on to the story ...

Over the years, I have assembled around two dozen AR platforms. Most were to sell when I had an FFL. I have noted with great interest the builds being created by members here. Some pretty cool stuff being done by some very talented people. I started wondering what if someone wanted a custom build and they …

a) Didn’t have all the tools required.
b) Didn’t feel they have the ability.
c) Didn’t want a readily available off the shelf “custom” build.
d) Had some very specific requirements that were not stocked by dealers.
e) Just didn’t want to do it themselves.

Would someone like Rainier Arms (my choice for this build) accept a parts list and build-to-spec something “special”?

So, I browsed their web site looking at my idea of dream pieces for a new upper for my SBR. Please note that the SBR - Short Barreled Rifle - is an NFA item and properly taxed and stamped. Requesting a barrel shorter than 16 inches, and not having a muzzle device pinned and welded can get you into a lot of trouble. (Sorry - another disclaimer was necessary)

The parts I selected (along with required adjuncts) were:

Rainier Arms Stainless Match .223 Wylde Barrel – 14.5” Mid-length 1:8 Twist
14.5" is about as short as I can find with a mid-length gas system.
Rainier Arms UltraMatch Billet Upper Receiver – MOD 2 (M4 Feed Ramps)

Syrac Ordnance .750 Set Screw Low Pro Adjustable Stainless Gas Block
I wanted an adjustable gas block for suppressor use. I also wanted the barrel drilled so the Gas Block could be pinned in addition to the set screws. The Syrac GB has a dimple in the appropriate location for drilling the barrel.

Gas Tube – Mid-length
Gas Tube Roll Pin
Rainier Arms BCG – Precision Match Grade Nickel Boron
Fortis Hammer Charging Handle – Black Teflon
AAC 5.56 51T Muzzle Brake – properly timed but NOT pinned – the suppressor mount.
Troy Front Folding Battle Sight – HK Style (not installed)
Troy Rear Folding Battle Sight – Not Installed
BCM KMR KeyMod Rail 5.56mm 13”
Assembly Fee
Gas Block Pinning Fee

I called Rainier and spoke with a technician. Nine days later the upper arrived at my door. Washington to Florida has to be a couple of days.

Could I have put it together myself – yes. Could I have purchased a built upper from anyone’s inventory – yes. Were the assembly charges less than the cost of all the tools required to put it together – not really sure, but would be very close. The workmanship was first class and backed by Rainier Arms.

Does it shoot? Oh yeah !

I put the new upper on the LWRC SBR Lower running their factory buffer spring and H2 buffer. Sight-in and shooting was done at GriffonSec’s.

I was actually surprised with the Troy Sights this time. I have them on most of my AR’s, and sight-in is always interesting (remember the box of chocolates line). This time, the vertical alignment of the front sight was “first shot perfect” and the windage was only off a couple of inches to the left at 25 yards. Empties ejected about six feet away between 3 and 4 o’clock. The empties moved a little closer to five o’clock with the suppressor on it, but not enough “over-gassing” to warrant adjusting the Syrac GB.

After adjusting the irons, I put a Leupold Mark AR Mod-1 1.5x4 Scope in a LaRue LT-104 QD mount on it. After a single shot zero (shoot one round, move the cross hairs to the hole) the next five rounds at 25 yards went into a single hole less than a half-inch wide. Grouping at 100 yards with PMC .223 Remington 55 Grain FMJ consistently shot less than 1.5” (ten shot groups using 68 year old eyes - no shots omitted from each group).

We ran a few drills with it on 12” steel at ranges from 35 to 125 yards and there were zero issues of any type with the unit.

I was impressed with the BCM KMR. I had not handled one, and selected it for this upper based on comments seen about its’ diameter and weight (some great photos didn’t hurt any either). I wanted a rail running full length, as close to the muzzle threads as I could get, and the 13” rail on a 14.5” barrel has the “look” I was after. I tried to come up with an analogy for the size of it in my hand, but couldn’t. Using my thumb and middle finger around the rail, I overlap by a knuckle. I don’t use the “C” grip style, but can hold it like the small end of a baseball bat.

I added a BCM Gunfighter KeyMod short vertical grip – this worked very well for me; I like stubby verticals.

This was an interesting experiment that turned out extremely well. I am very pleased with the upper, and many thanks go to the build team at Rainier Arms.

Bottom line – if you want a custom upper and you fall into any (or all) of the categories a) through e) listed above, pick out your parts and give Rainier a call.

As received from Rainier:



AAC Brakeout 51T:



Rainier Upper, BCG and Fortis Hammer:



Completed upper on the LWRC SBR Lower: