RC1 — a lightweight tactical carbine | GridScout™

GridScout™ Follow

Pursuit of proficiency in the manly arts, like maps and knots and locks and guns.

GridScout Gazette™ presents:

RC1 — a lightweight tactical carbine

I’m building a new weapon. I call it the GridScout™ RC1. Why RC1? Because it’s easier to explain that RC1 stands for Reeder Carbine One than to explain that PK6 (its original name) stands for Piŝta Karabeno je 6,5mm Grendel.

Weapon design

I want a gun that’s especially easy to handle in close-quarters combat without sacrificing effectiveness at medium range (up to 500 yards). While a PDW may be great in close quarters and an M4-style carbine is pretty good up to 300 yards, both are severely handicapped beyond that range. A PDW’s range suffers from its very short barrel, while the carbine is typically held back by a diminutive 5.56x45 NATO cartridge. In either case, the energy of the bullet is insufficient to remain 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 puppy.)

As an illustration that 5.56x45 won’t do, consider that at 500 yards it will have lost 68% of its kinetic energy, reducing it to just 541 ft·lb. While there’s no universal agreement on how much it takes to do the job well, I set my requirement at 800 ft·lb based on the guidance of Chuck Hawks. A 6.5 Grendel cartridge exceeds this slightly at 500 yards, giving 818 ft·lb; whereas the lighter and less streamlined 5.56mm cartridge can comply only out to 300 yards. (Calculations based on Wolf™ Military Classic cartridges — 6.5 Grendel, 100gr, 0.515 BC, 2723 ft/s MV; vs .223 Remington, 55gr, 0.395 BC, 3241 ft/s MV.)

Basis

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 for modern carbines. The Incursion, however, isn’t everything that I want it to be.

It’s slightly longer than I prefer in close quarters, and 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.

Barrel

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. To minimize length, no muzzle device will be mounted on the barrel.

Buttstock

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.

Sights

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

Progress on this project is as follows.

This carbon-fiber buttstock, produced by Incognito Arms™ within spitting distance of my daily commute through Boise, weighs just 2.33 oz. The 13° Ergo™ Swift Grip (2.8 oz with included screw) notably has no backstrap, so the palm can grip the gun higher for recoil management and easier reach of the magazine release. I've also installed an Alexander™ Incursion melonited chromoly barrel (1 lb 7.9 oz), Aero™ barrel nut (1.3 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. A TacStar™ handguard is pictured but turns out to be incompatible with the piston. 2018-12 — Buttstock, grip, & barrel

Velocity™ 4-lb trigger, 3D-printed copolyester trigger guard, V7™ short-throw titanium selector, Seekins™ enlarged bolt-release paddle, Aero™ lower parts kit, ArmaSpec™ stealth recoil spring. 2020-06 — Trigger & guard, selector, mag release, & assorted lower innards

This enormous mag-well flair, 3D-printed of carbon-fiber copolyester, makes my magazine changes so much faster. 2020-06-25 — Flaired magazine well

The carbon-fiber handguard lacked piston clearance, so I switched to this aluminum model by Intacto Arms. Also new is the steel thread protector by Down Range Products. 2021-04 — Handguard, front sight, & thread protector

Projected total weight, with a scope and a full magazine, is 7 lb 1 oz. Total length is 31 5/16 inches.

Coming 2021-06 — Weaver K6 riflescope

Performance

When the RC1 is complete, Leeroy and I will assess its performance in a separate post. We’ll compare it to a couple of other guns. Criteria will include:

  • Ease of maneuvering in close quarters
  • Speed of magazine changes
  • Ability to reliably (4 shots out of 5) hit the vital areas of men and wolves:
    • At 25 yards with iron sights, quickly (2 seconds max per shot) in standing position
    • At 50 yards with iron sights, in standing position
    • At 75 yards with iron sights, in kneeling position
    • At 100 yards with scope, in kneeling position
    • At 300 yards with scope, in prone position
  • Muscle fatigue from a long day of shootin’

Comment Subscribe [weapon rc1 carbine]