*Update: We reached out to Martin Grier to ask about some of the more stunning claims surrounding the rifle and heard back just after the original article went to press. We've updated, in bold, the muzzle velocity and fire rates below with his response.
*Second update: After another discussion with Martin Grier, the inventor of the weapon, we've learned that some of the reporting on the weapon's firing action is incorrect, and we had originally repeated those incorrect claims. We've corrected the reporting in bold.
The Army is requesting a prototype of a personal rifle that has four bores, triggering headlines everywhere — but the bigger news might be that the manufacturer claims that it cannot jam, is electrically fired, and weighs less than today's common weapons.
First, let's discuss the "four barrels" thing that's flying around the internet. FD Munitions actually describes their prototype with five openings as a five-bore design — and that's more accurate. The weapon has a single barrel, meaning a single bar of metal, but that bar has five holes in it, each of which lines up with a bullet when the weapon is loaded. The Army version would have four bores and, consequently, four bullets.
And, we're using "bullet" here instead of "round," the general military term, intentionally. Rounds are self-contained units with propellant, projectile, and primer. Most of them also have a case. But the L5, FD Munitions' prototype that will feed into the Army's requested design, uses blocks of ammo instead.
In the block ammo, a single block of composite material has multiple hollows carved out. In the case of the Army proposed prototype, it has four hollows. Each hollow is filled with propellant, a firing pin, and a bullet that is precisely aligned with a bore. When the shooter fires, an electronic charge triggers a firing pin striker, igniting the propellant, sending the bullet down the bore and towards the target.
The FD Munitions L5 rifle prototype has five bores and few moving parts. The Army has requested a four-bore version for testing.
The shooter would still typically fire one round at a time. The bores are stacked vertically as are the "blocks" of ammo. Each trigger pull typically fires the next round in sequence. When four rounds have been fired, the first "block" of ammo is ejected and the next block is loaded.
But, when necessary, the shooter can tell the weapon to fire the entire block at once, sending four 6mm rounds flying at once.
All of this allows for a system with much fewer moving parts than a traditional, all-mechanical rifle. FD Munitions claims that, since only the blocks are moving and they only move 0.5 inches at a time, the weapon has a minimized probability of jamming. And, since most of the heat of the weapon firing stays in the block, which is soon ejected, the weapon has much less chance of overheating.
The FD Munitions L5 rifle prototype fires rounds from "blocks" of ammo via electric actuation instead of a mechanical hammer.
But, of course, the Army has to test all of this before it can make a decision — hence the prototype.
We heard back from the inventor, Martin Grier, about the firing rates and velocity just after we originally went to press. Here's what he told us about the numbers (light edits for clarity):
The velocity quote of 2,500 mph is close, with velocities of 3,400-3,600 fps. achievable with our composite Charge-Block ammunition (depending on projectile mass). The COPV (composite overwrap pressure vessel) design is much stronger than steel and can safely operate at 80k psi.
The maximum theoretical rate of fire with our electronic fire control is about 6,000 shots per minute (SPM) in full-auto mode, since the pulse width is 10ms. (1/100 sec.)
In burst-fire mode, That rate goes up to 7,500 spm since the pulses can be overlapped somewhat for short periods.
In actual use, for a personal weapon, 4-600 spm in full-auto mode seems to be the most controllable, just as with other weapons, and in burst fire 1,800 spm is the sweet spot.
Since the tech is fully scalable, in other applications, such as [Squad Automatic Weapon], or other crew-served weapons, different rates of fire may be more useful. The electronic fire control can be easily set for any rate up to the maximum.
The blocks of ammunition contain four to five bullets each and, when ejected, take a lot of the heat with them, allowing the shooter to fire more rounds before the weapon overheats.
The Army would need to verify those rates. And, it would need to know at what ranges the weapon is accurate in both standard firing and when firing four rounds simultaneously. Do the rounds affect each other in flight when traveling so close together at such high speeds?
And how much weight would a combat load be with the metal blocks? They certainly contain more material than four loose rounds would, so would an infantryman need to carry significantly more weight? And while the ejected blocks may take a lot of the heat with them, there's still the friction of the rounds traveling down the bores with the exploding gasses to heat up the barrel. What's the sustained rate of fire before it overheats?
While the Army digs into all the numbers and tests things like reliability and heat dissipation, the rest of us can talk about how cool it sounds. It's like a video-game weapon come to life.