AR-MPR: Lower Assembly Parts List

In my last AR-MPR post, I gave an overview of the parts that will be used to assemble the AR-MPR upper assembly. In this post, we’ll take a look at the rest of the rifle- the lower assembly (OK, there’s also optics and accessories, we’ll but we’ll cover those later).

I started this project with nothing more than a DPMS stripped lower in hand- and that’s going to serve as the foundation for the lower build, and everything else for the lower assembly will be assembled on top of this block of aluminum. Since it’s got the serial number, legally the stripped lower receiver *is* the gun. That’s the great thing about building an AR-15 from scratch- all you need is a stripped lower receiver, and you can then order the rest of the parts online**.

**Check your local laws and regulations to make sure that your rifle conforms to those regulations, otherwise, you could get yourself in trouble!

OK, once you’ve got your lower receiver and know what you can order and build, it’s time to come up with the list of parts that you’ll use. For this project, I have two goals for the lower receiver (the whole rifle really):

  1. Quality parts that will assemble well, last a long time, and perform reliably
  2. A trigger that will enable precision shooting (reduce variations in point of aim due to trigger dynamics)

So, by working with Larry Weeks at Brownells, we came up with the following list of parts for the lower assembly (including the buttstock). You can click on the links to get more product information.

AR-MPR Lower Parts List:

7075-T6, aircraft-grade aluminum receiver is forged and tempered for strength, just like the M16 lowers used by the U.S. military. CNC machined and ready to be the foundation for your match, tactical or hunting rifle. Hard coat anodized to mil-spec 8625 for durability; Teflon® coating gives additional lubricity and an attractive, matte, black finish.

Lower Receiver Parts Kit (High Standard)
Convenient kit contains all the parts needed to complete a stripped, small-pin, semi-auto lower receiver. Saves time and money—no need to hunt down each item individually. These high-quality parts are manufactured to precise tolerances in accordance with MIL-STD 105D to ensure correct fit in a mil-spec receiver. Includes complete trigger/hammer group with precision-ground engagement surfaces for a smooth, clean trigger pull and crisp release. Aluminum triggerguard with pre-installed detent pin resists impact and won’t crack in cold weather. High-impact polymer pistol grip is original A2 style with single finger groove on the front, vertical serrations on the backstrap, and checkered panels on the sides. Add the receiver extension/buttstock system of your choice, and your rifle’s bottom half is complete.

Two Stage Match Trigger – .154″ Hi-Speed DMR (GEISSELE AUTOMATICS)
Fully adjustable trigger gives a smooth, two-stage pull with a precise “icicle sharp” break and ultra-fast lock time to minimize accuracy loss caused by gun movement during trigger pull. Set first stage pull weight by bending the legs of the trigger spring; set second-stage weight within a pre-set range by turning its adjustment screw. Another screw on the trigger lets you adjust overtravel for clean, crisp letoff. Lightweight hammer provides a 50% reduction in lock time over factory hammer, yet uses standard weight hammer spring to ensure sufficient energy transfer for reliable primer ignition, even on AR-style .308 weapons. Trigger shoe is positioned 1/8″ farther forward than factory shoe for comfortable finger position during the squeeze. All contact surfaces are wire EDM cut to exact dimensions for full, precise engagement free of unwanted play. Available to fit both large (.169″) and small (.154″) pin receivers; small pin models include spare hammer pin to aid in proper fit on receivers with slightly oversized holes. Service model provides nominal 4½ lb. pull weight required for NRA High Power Service Rifle competition and is also approved for CMP-sanctioned competitions. Most of the pull weight is loaded on the first stage, followed by a quick, clean second-stage break. First stage, 3.2 to 5 lb.; second stage, ½ to 1½ lb. Match model allows a very low combined pull weight for superb trigger control on highly modified raceguns used in unlimited NRA High Power Rifle competition. Helps you shave those extra hundredths of an inch from your groups for a competitive edge. First stage, 1.3 to 3 lbs.; second stage, 4 oz. to 14 oz.

AR-15 Molded Rubber Pistol Grip (Hogue)
Non-Slip Grip Surface; Increases Comfort. Strong, fiberglass insert fits solidly against the frame, resists wear, won’t loosen. Orthopedic design with palm swells and finger grooves reduces shock, increases shooting comfort; maintains a stock appearance.

A2 Rifle Stock Completion Kit (Brownells)
Convenient kit contains all the components needed to mount the buttstock of your choice on an AR-15 rifle or carbine. Perfect for stock conversions such as altering a rifle to accept a collapsible carbine stock. All parts are manufactured from the highest quality materials and held to strict dimensional tolerances for proper fit and function. Kits available for the four standard buttstock types. A1 rifle kit contains receiver extension tube, recoil buffer, recoil buffer spring, and buttstock cap screw. A2 rifle kit adds to A1 kit contents the correct buttstock spacer required for A2 rifle stocks. Carbine kits contain receiver extension, carbine recoil spring, carbine recoil buffer, lock ring, and receiver plate. Commercial carbine kit comes with 1.17″ O.D., six-position receiver extension for use with commercial or “universal” buttstocks. Mil-Spec kit has a 1.14″ O.D., five-position receiver extension for correct fit of military M4 carbine buttstocks. M4 buttstocks and clones will not fit Commercial tubes.

AR-15/M16/M4 Collapsible Buttstock (Brownells)
Rugged, Six-Position Adjustment For L.O.P. & Easy Storage

Oversized Triggerguard (Brownells)
Protects Trigger During Rough Handling & Allows Fast Access Even When Wearing Gloves

That should be all that’s required to get the lower put together. I’m expecting to make some changes as needed depending on how things go during assembly. One of the things I’m wondering about is whether or not the traditional collapsible A-4 style stock will be rigid enough for accurate long distance shooting. I do like the fact that it will make the rifle more compact for storage and packing during hunting.

We haven’t talked about tools and fixtures yet, and we’ll save that for the next AR-MPR post. Anything you’d change or add here? Am I missing anything? Please leave a comment!

See ya,

6 thoughts on “AR-MPR: Lower Assembly Parts List”

  1. You shouldn’t need the “A2 Rifle Stock Completion Kit” listed above. That appears to be for installing a fixed A2 style stock. The “AR-15/M16/M4 Collapsible Buttstock” looks to include everything you need for the butt stock. Unless I’m missing something?

    1. Thanks Mike, I was wondering about that. I’m also wondering if I’ll get a fixed stock because of the lack of rigidity of the collapsible unit. I guess we’ll see!

    1. The big reason here was I wanted to be able to tune the trigger’s release pressure way down. I believe if you want to be down in the 16oz range or less, this trigger is the best option.

  2. I have a 1/4 MOA AR-15 – Here is what my lower is

    Magpul PRS Stock
    Tubbs Flat-wire buffer spring
    DPMS Buffer
    Mil-spec extension tube
    Double Start Lower
    JP Trigger
    JP Take-down pin
    Ergo hand grip

    Looking into the GEISSELE trigger to tighten my groups – I may go billet upper and lower as time goes on…

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