January 08, 2019
Photos by Mark Fingar
Don’t argue with The Man. Bureaucrats aren’t used to anyone or anything challenging their authority, so when the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) says a stockless AR-15 is a pistol, the correct answer is “roger that.”
This mighty fine pistol comes to us from FN and is creatively titled the FN 15 Pistol, .300 BLK. Of all the AR pistols floating around out there, this one makes the most sense to me. It has the right barrel length, barrel type and gas system length, and it’s chambered in the only cartridge ideally suited for such a firearm.That Barrel, Tho
FN makes an f’n awesome barrel — no lie. They’ve been hammering barrels out for several decades, and until recently, Uncle Sam got them all. FN made M16A4s for the U.S. Marine Corps and sold tens of thousands of them to the government over a couple of decades.
FN hammer forges their barrels, and that’s the best way to make a barrel last. Hammer forging works by placing a short, thick piece of steel tube on a mandrel. The mandrel is a precisely machined, hardened steel rod that is a mirror image of a barrel bore. Huge hammers descend on the steel tube and beat it around the mandrel until it’s the shape of a barrel. It’s loud and takes a few minutes, but the process creates the most durable barrels.
The durability comes from the hammer-forging process. As the hammers beat on the steel, the steel next to the mandrel gets squished every time a hammer strikes. This work-hardens the soon-to-be barrel bore, making it resistant to the heat and pressure that the bore contains.
This super-sweet hammer-forged barrel from FN is cut to 12 inches in length, has a pistol-length gas system and is chambered in .300 BLK. Each aspect of this barrel is ideal for general use and personal defense. Even the barrel contour is right on time.
Enthusiasts who geek-out on .300 BLK will want to argue about what makes the ideal barrel length and twist rate for the cartridge. Special Operations Command (SOCOM) liked a 1:5-inch twist rate to stabilize heavy subsonic bullets but found that the bullet they were using at the time spun so fast that it started to open up as soon as it left the muzzle. The bullet was a heavy, monolithic projectile with large petals. The extreme rotational velocity pulled the petals away from the center and raised hell when fired through a suppressor.
Next up was the 1:6-inch twist rate. It had a brief service life because it did a good job with heavy subsonic bullets without spinning them so fast that the exotic monolithics expand prematurely. SOCOM changed bullets and went back to the 1:5-inch twist because they have a heavy focus on subsonic applications and want the ability to shoot them as far as possible.
I’m not interested in expanding subsonic bullets for general use because it seriously handicaps the terminal effects of the .300 BLK. Subsonic is nice for a couple of shooting scenarios, but supersonic is where it’s at. An increase in velocity means lighter bullets, so you can slow the twist rate and still get great stability. Most commercially available .300 BLK barrels have a 1:7-inch twist rate because it does so well with both supersonic and subsonic projectiles.
This FN pistol has a 1:7-inch twist, and the 12-inch barrel leaves enough room for a forend that can support a horizontal grip, light and more. The .300 BLK was designed for use in a 9-inch barrel to meet size requirements for a military unit looking to replace their HK MP5s. While the 9-inch barrel certainly works, a 12-inch barrel is ideal for general use and personal defense.
Forend real estate is not to be taken lightly. Most shooters of really short barrels stay on the flat range. As soon as you step into the positional shooting environment (which, coincidentally, looks a lot more like real-world shooting scenarios), real estate becomes vitally important. The extra space up front allows you to rest the forend on whatever you’re hiding behind and also gives the shooter options on support hand placement. Rollover prone while shooting under a vehicle is a great way to learn why super-short barrels are not your friend. Twelve-inch barrels are better suited for AR pistols.But It’s a Pistol
It’s fitting that this pistol has a pistol-length gas system. Many shooters might not realize that while the .300 BLK is commonly chambered in rifles and considered a rifle cartridge, it is loaded with pistol powder. In fact, if you look in Hornady
’s reloading manual, you’ll find the .300 Whisper (.300 BLK’s identical twin) in the pistol cartridge section.
The .300 BLK is a rifle cartridge because SAAMI says so, and it’s loaded to rifle pressure. SAAMI maximum pressure for the .300 BLK is 55,000 pounds per square inch (psi) while most pistols top out at 35,000 psi. However, the pistol powder in the case burns quickly and pressures drop fast as the bullet moves down the bore.
A pistol-length gas system on a 5.56mm rifle sounds like a risky proposition, but it’s a great idea for the .300 BLK. Pressure drops fast enough in the bore that the short gas system on this FN pistol allows the gun to cycle reliably with both supersonic and subsonic rounds (subsonic rounds will need a suppressor for reliable operation). No adjustable gas block is necessary to control bolt velocity. It’s a pretty slick setup.
Having the option to freely move between the two types of loads without tinkering with a gas block means the shooter can use supersonic ammo for hunting and general use, then switch to subsonic and a suppressor for home defense.
FN’s AR pistol in .300 BLK is an excellent choice for home defense. If you don’t like shooting with a bare buffer tube, it comes with the SBX-K arm brace, and the ATF says it’s OK for the brace to touch your shoulder like a stock. Once you get it to your shoulder, it’s much easier to provide accurate fire, even under high stress.
Subsonic ammunition in this pistol will have very low chamber pressure (right around 20,000 psi) that drops fast once the bullet starts moving. Most of the noise from shooting a gun comes when the hot-burning gas exits the muzzle under high pressure. The pressure behind the bullet when it leaves the barrel is called exit pressure. The higher the exit pressure, the louder the gun. This is why short-barreled rifles (SBRs) are obnoxious.
Exit pressure on this 12-inch barrel with subsonic ammunition for home defense will be lower than what’s found in almost any pistol. I love the idea of not destroying what remains of my hearing should I ever need to defend my home. In order to get reliable operation with subsonic ammunition without a suppressor, a lighter buffer spring is required.Burning Powder
FN put a couple of nice touches on the FN 15 Pistol that make it more pleasant to shoot. Since it is a pistol, it will move around more in your hands when firing than a rifle. FN uses a Magpul triggerguard that fills the gap between the grip’s frontstrap and the triggerguard, smoothing this transition. Spend a day at the range without that gap filled and you’ll have no skin on the inside knuckle of your firing hand’s middle finger.
FN also uses Magpul’s MOE grip, which is my preferred AR grip. It is simple and textured in the right places; it is big enough to fill your hand and allows for great control of the pistol.
All the critical operating components are what you’d expect from a quality AR-15 manufacturer. The carrier key on the bolt carrier and the castle nut on the buffer tube are both staked correctly. There’s no sense in putting an almost immortal barrel on this pistol if the gas key comes loose or the buffer tube starts rotating after a few hundred rounds.
FN also adheres to all the standard testing and quality control procedures outlined by the military. Bolts and barrels are pressure tested and magnetic particle inspected. Bolts are made from Carpenter 158 steel and carriers from 8620 steel. Fit and finish on the receivers are also much better than run-of-the-mill AR stocks. The anodizing was even and deep, and the receiver fit was ideal.
The pistol was also more accurate than I expected. Normally, a good hammer-forged barrel will average 1.2 to 1.3 MOA for five shots at 100 yards. The FN pistol averaged 1 MOA, with some groups running sub-MOA. That is rare and speaks well of FN’s barrel-building prowess.
Between the .300 BLK’s low pressure, small powder charges and the hammer-forged, chrome-lined barrel, this pistol will last forever. It is highly portable, accurate and a good fit for just about anything you have in mind.
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