RC1 — a lightweight tactical carbine | GridScout™


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RC1 — a lightweight tactical carbine

The ultimate purpose of the GridScout™ map-search tool is to provide for a better community defense. For that same purpose, I’m building a new firearm. I call it the RC1. Why RC1? Because it’s easier to explain that RC1 stands for Reeder Carbine #1 than to explain that PK6 (my original name for the RC1 concept) stands for Piŝta Karabeno je 6,5 Grendel.

Weapon design

My intent is to create a weapon that is especially easy to handle in close-quarters combat without sacrificing effectiveness at medium range (up to 500 yards). While many PDWs are very good at close quarters and a typical modern carbine is pretty good up to 300 yards, both are severely handicapped beyond that range. The PDW’s biggest hindrance in this regard is its very short barrel, while the carbine is held back primarily by its use of the diminutive 5.56x45 NATO cartridge. In either case, the energy of the bullet is insufficient to remain very effective at my maximum intended distance against human targets and the occasional medium-size game animal. (Besides the obvious counterterrorism missions, I intend to hunt wolves, deer, and wild boar with this weapon.)

As an illustration of the insufficiency of 5.56x45, consider that at 500 yards it will have lost 68% of its kinetic energy, reducing it to just 541 ft·lb. While there is no universal agreement on how much it takes to do the job well, I set my personal requirement at 800 ft·lb per the guidance of Chuck Hawks. A 6.5 Grendel cartridge exceeds slightly at 500 yards, giving 818 ft·lb; whereas the lighter and less streamlined 5.56mm cartridge can comply only out to 300 yards. (These calculations are all based on the Wolf™ Military Classic cartridges — .223 Remington, 55gr, 0.395 BC, 3241 ft/s MV; and 6.5 Grendel, 100gr, 0.515 BC, 2723 ft/s MV.)

I think I can more fully achieve my own goals by creating a custom carbine than by selecting any of the off-the-shelf offerings that I’ve already considered. So I’m going for it, and upon completion we’ll see how it performs.

Until we have those results, I’m just another guy on the Internet who thinks he knows everything. ;)


The RC1 design is based somewhat on the Alexander™ 6.5 Grendel Incursion, which is relatively light and fires one of the most effective general-purpose cartridges yet devised for modern sporting rifles. The Incursion, however, isn’t everything that I want it to be.

It’s slightly longer than I prefer for close-quarters maneuvering. More importantly, it still relies on the direct-impingement gas system that got M16 operators killed in Vietnam.

But thanks to the versatility and popularity of Eugene Stoner’s modular AR-15 design —upon which the M16 and the Incursion are based—, we now have a standardized means of interchanging parts to fit the needs and wants of the shooter. The RC1 will take advantage of this in two important ways.

  • Certain part selections, inspired by PDWs and by AR15A3-derived ultralight carbines, will serve to make the RC1 lighter and more maneuverable.

  • The bolt will be cycled by a gas piston, based on the Armalite AR-180 design, which has proven substantially more reliable than direct gas impingement.

Piston gas systems consistently outperform direct-impingement systems in reliability tests, as they did in a 2007 test by the U.S.Army.


The barrel of the RC1 will be of the standard 16” carbine length, just long enough to avoid the red tape associated with a short-barreled rifle. This length also produces high enough muzzle velocity and bullet energy for practical medium-range use. The muzzle brake will be a short, single-chamber model to minimize the added weight and length.


The RC1 will have a very short, fixed-length buttstock to shift its mass closer to the shooter’s body where it’s most easily supported. With the 33° grip angle that’s most common in modern carbines, this position would be uncomfortable for the wrist of the shooter’s dominant hand; so the RC1’s grip will instead be nearly vertical as in a PDW. This weapon will be as lightweight as practicable, in order to limit muscle fatigue so the shooter can more easily keep his sights steady on the target.


The RC1 will be equipped with two sighting systems:

  • A lightweight fixed-power riflescope, for 100- to 500-yard engagements
  • Simple offset iron sights for quick target acquisition within 100 yards


Progress on this project is as follows. Initially, a few paper parts stand in for some of the major parts that I have not yet acquired. With a scope and a full magazine, I anticipate a total weight of about 6 lb 13 oz, and a total length of about 32 inches.

This carbon-fiber buttstock, produced by Incognito Arms™ within spitting distance of my daily commute through Boise, weighs just 2.33 oz. Compared to other stocks with an integral buffer tube, it appears to be the lightest on the planet. I plan to use a fixed-power scope such as the Weaver K6 (9.8 oz + rings). As the other paper-doll accessories show, I plan to use the 14° PDW grip by Tactical Link™, an E-Lander™ 17-round steel magazine, an Alexander™ Incursion barrel, and a very short muzzle brake. 2018-07 — Buttstock & paper mockup

The 13° Ergo™ Swift Grip (2.8 oz with included screw) notably lacks the backstrap of the originally planned Tactical Link™ PDW grip, allowing the palm to rise slightly for better recoil management and extending the index finger forward toward the magazine release that so many people otherwise need to enlarge for ease of reach. The Alexander™ Incursion melonited chromoly barrel (1 lb 7.9 oz), Aero™ barrel nut (1.3 oz), and TacStar™ handguard (7.3 oz with included hardware) are also installed. Total weight as pictured is 3 lb 5 oz. The barrel came with an Alexander™ "hard-use" bolt assembly (1.5 oz), which in the absence of a bolt carrier is not yet installed. 2018-12 — Grip & barrel

This 3D-printed trigger guard is based on a model by Gregory Spicer.

For visualization, I mounted some cheesy airsoft-quality offset sights and a scope borrowed from another rifle. 2019-05 — Mockup


When the RC1 is complete, I will assess the performance of this weapon in a future post. I’ll provide a link here to make it easy on you.

tags: weapon - rc1 - carbine

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