RC1 — a lightweight tactical carbine

2021-04-13 — by Jeremy Reeder

I built 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 wanted 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 takes advantage of this in two important ways.

Certain part selections, inspired by PDWs and by AR15A3-derived ultralight carbines, serve to make the RC1 lighter and more maneuverable.
The bolt is 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 is 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 has a very short, fixed-length buttstock to shift its mass closer to the shooter’s body where it’s most easily supported. If it had the 33° grip angle that’s most common in modern carbines, then it would be uncomfortable for the wrist of the shooter’s dominant hand; so the RC1’s grip is instead nearly vertical as in a PDW. This weapon is meant to 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 (not yet mounted), for 100- to 500-yard engagements
Simple offset iron sights for quick target acquisition within 100 yards

The Product

This Anderson™ AM-15 receiver set (8.7-oz lower, 6.7-oz slick-side upper) from Wisconsin has no ejection-port cover and no forward assist, frills which in my view aren't worth their weight. The receivers are held together by 2A Armament™ titanium takedown pins made in southeast Boise, adding 0.1 oz. This 5.9-oz E-Lander™ magazine from Israel is made of steel, making it stronger than the aluminum USGI models that are prone to bending of the feed lips. 2018 — Receivers, pins, & magazine

2018-12 — Buttstock, grip, & barrel

The Fortis Clutch charging handle weighs in at 1.06 oz. It's single-sided, but this is the only side that has a real function in mil-spec charging handles anyway. As pictured, the weight is now 3 lb, 12.1 oz. The endplate has a quick-detach mounting point for a sling. The ratcheting nut doesn't require staking. Both are produced by Primary Weapon Systems of Boise, just around the corner. 2019 — Charging handle & endplate

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

Adams Arms™ lightweight bolt carrier, adjustable micro gas block, & piston Adams Arms™ piston kit & GGG™ Transition rear sight. Also pictured is a plastic thread protector, but that'll be replaced with a steel one better suited for the heat. 2021-03 — Piston kit & rear sight

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.

Performance

It shoots good. ;)