Roll Your Own – Building Your Own Lightweight AR-15

Steven Kuo – Recoil Magazine

Building Your Own Lightweight AR-15

If you’ve read through the past five pages on the OIP rifle, you’ve seen what three grand (or more) will buy from a custom rifle builder. It’s a hefty price tag, but you get a purpose-built weapon that’s well-sorted, perfectly tuned, and fully optimized. But what does it take to roll your own lightweight AR-15? It’s the golden age of the AR platform, with a mind-boggling array of components available to suit every imaginable use and taste. So, utilizing freely available components and with an eye on your pocketbook, what can you pull off in your own workshop?

Death by a Thousand Cuts

Bentwood Gunsmithing achieved extreme weight savings in their OIP carbine by lightening every part of the rifle they could. The problem for home builders is the expense of acquiring the lightest available alternative for every single part — and even then Bentwood invested in additional customization and gunsmithing work. We sought to put together our own lightweight build for less scratch, though we’ll tell you upfront that it’s still not cheap…nor is it the prettiest rifle you’ve ever seen.

The heaviest parts in an AR-15 are typically the barrel, handguard, upper and lower receiver, and buttstock. We targeted those components first for hefty weight reductions and justified some splurging here to avoid compromises in function. Fortunately, we found a very reasonably priced pencil barrel from Faxon, the same manufacturer as used by Bentwood. While their 14.5-inch version was very light at 17.5 ounces, and its mid-length gas system tempting, as home builders we opted for their 18.8-ounce, mid-length, 16-inch barrel. This meant we avoided pinning and welding the muzzle device, preserved serviceability, and let us take advantage of the wee Taccom compensator since we didn’t need to extend overall length to 16 inches. Compare this to M4 profile barrels, which can range from 1.75 to just over 2 pounds.

For the handguard, we chose one of our favorites, BCM’s popular KMR, made of aluminum-magnesium alloy with a full top rail and KeyMod all around. It’s a great combination of functionality and reduced weight, but it’s a bit pricey. We selected a 13-inch variant as a compromise between versatility and weight — 7.5 ounces including the barrel nut, as compared to cheese-grater Picatinny handguards that can clock in at a pound and beyond for 12-inch versions. Opting for the 10-inch KMR would save you 1.1 ounces, and upgrading to the 15-inch adds 0.7 ounces. For those watching their budget, a 12-inch carbon-fiber handguard from AP Customs provides a 30-percent cost savings with similar weight and one less inch in length.

There are a couple lightweight aluminum AR receiver sets, including the Battle Arms Development BAD556-LW (similar to the OIP) and the 2A Arms Balios, featured in Issue 16. However, they’re both quite expensive at $550 and $520, respectively. To save some cash, we went with X-7 Fusion polymer receivers from Kaiser Shooting Product, which cost less than the lightweight aluminum sets at $399 for the set. While reading the words polymer and AR receiver placed next to each other, you might have some reservations — as did we. But Kaiser’s offering is unique in its use of aluminum inserts at key locations: the trigger and hammer pin holes, the receiver extension threads, and the pivot and takedown pin holes. Fears were further allayed when we learned Kaiser stands behind the X-7 with a lifetime warranty. At a combined weight of 11.1 ounces, they’re quite a bit lighter than typical forged receivers, which are almost a pound.