So make yourself an ARK: Fishbreath builds an AR-15

That’s right. It finally happened.

Of course, it’s me, so I built it from a lower parts kit (some years ago) and random upper parts (a few days back), not simply by pinning a prebuilt lower and upper together.

Oh, and it’s in 7.62×39. That’s right: an AR-15 in 7.62×39. A 7.62×39 AR-151.

First thing’s first. Why ARK? Well, I have two existing 7.62×39 rifles. One is the BRK, the Bullpapniy Russkiy Karabin. Another is Kat, which is my competition Russkiy Karabin, or CRK. There’s an obvious theme developing here, so ARK it had to be. In traditional Fishbreath rifle naming style, the acronym has two meanings. The first, most obvious one is that the rifle is an AK caliber in an AR pattern: AR-K. The second is the also-traditional Russian name, the Amerikansko-Russkiy Karabin.

Why build an AR-15 in 7.62×39, you ask? I have a few reasons. First: it’s a deeply underrated caliber. It can do everything .300 Blackout can do, although I grant it’s harder to find subsonic 7.62×39 than .300 Blackout. In ballistic terms, the two cartridges are so nearly identical that the drop-compensating reticle in my chosen optic works for both with the same zero. The difference between the two comes down not to innate capabilities, but to modern development effort2.

Second: the AR platform is admittedly pretty neat. I can hardly deny that the ergonomics are good, and the Lego-for-adults aspect is deeply appealing to me, an adult who rather wishes he had more Legos.

Third: I can’t abide by being so normal as to build an AR in 5.56. Parvusimperator often accuses me of being a gun hipster… and I absolutely agree. An AR-15 in 5.56 does very little to interest me: hipsterish though this sentence may be, it’s played out. 7.62×39 is much more oddball, and therefore more interesting as an exercise.

Fourth: ammo is super-cheap, even if I have to pop by a local gun store. Much ink has been spilled on this front, so I won’t spend too much time on it. Suffice it to say that I don’t even mind having to occasionally pay friendly local gun shop prices for 7.62×39.

To be honest, though, it’s mostly the hipster factor. 7.62×39 AR is an odd combo, I like odd combos, and most of all, I like building things. Let’s get into the nitty gritty on parts.

Lower receiver
Surplus Ammo in Washington State, which is mainly a surplus ammo outfit, also makes decent forged lower receivers. It’s a lower. How much is there to say?

Lower parts/furniture
I got the standard Palmetto State parts kit, minus grip and stock. All the mechanical/internal gubbins are the same, with the exception of the trigger and hammer pins. I went with versions retained by wee c-springs for those, since I’d been hearing horror stories about the pins coming out under use at the time. It seems unlikely, pressing on the pins with my thumbs now, that they might, but better safe than sorry.

For the grip and stock, I went with the sadly-discontinued ATI Strikeforce set. The grip is heftier than most AR-15 grips, swelling to actually fill an average-sized hand, and nicely padded. The stock has an adjustable cheek riser which I’m not currently using, and is also padded. I purchased this set when I was planning to make this lower a 6.5 Grendel rifle, so that explains the slightly more marksman-oriented setup.

Upper receiver
Again, I went to Surplus Ammo, who had a billet upper in stock, charging handle included, for $75 delivered. I have a hard time arguing with that. It has a dust cover and a forward assist, as the Army intended. No side-charging or anything like that. It’s a $75 receiver. You can’t expect much beyond the standard for that money.

Faxon Firearms makes a 7.62×39 barrel with a 1-8″ twist. Unfortunately, it’s built to the surprisingly odd government profile, but crucially, it has a much larger gas port than your average 5.56 barrel. Since 7.62×39 is a lower-pressure cartridge by a significant margin, the extra gas port diameter is all but a requirement for adequate functioning.

The 1-8″ twist is also nice: a faster twist can better stabilize a heavy cartridge, and if I eventually load subsonic ammo for this rifle, that’s a handy trick.

Bolt carrier group
LJ’s AR Parts, who I had not heard of until I built this rifle, make a nitride BCG with an extended firing pin for better primer strikes on the harder primers of the standard cheapo steel-case ammo often fired through 7.62×39 rifles. That’s the one I’m using.

Gas block
I got one of the low-profile ones wot attaches by set screw. I prefer set screws to pins in basically every case.

Parvusimperator had a spare Troy Industries 9″ jobber lying around. It’s a nice lightweight handguard, ventilated so it doesn’t get hot easily. It also avoids the quadrail problem of heavy rails you don’t need by having a single top rail with attachable sections for other accessories.

Muzzle device
I went with the Strike Industries King Comp, which is well-reviewed and seems effective enough. In my estimation, it works better than the AK-74-style brake. Happily, it’s not quite as bad in terms of side concussion as Parvusimperator’s favored brakes, although it does considerably increase the noise. Factoring in my ear protection, I had a hard time differentiating the report from Parvusimperator’s Garand and the ARK.

Ordinarily, these wouldn’t merit mention, but this is a 7.62×39 AR-15 we’re talking about, and standard magazines need not apply. I found Midway’s house brand, AR Stoner, works fine.

Finally, the bit I alluded to at the very beginning. I chose a fancier optic than is my usual wont: the Primary Arms 1-6x ACSS scope for 7.62×39/300 Blackout. I have to say, I’m sold on the concept: an illuminated variable-power optic with 1x or near-1x magnification on the low end, for use as a red dot-style sight close up, and a bullet drop compensation reticle for longer-range work. This one is a particularly nice example. Parvusimperator, that noted glass snob, said the glass is “not bad”. The reticle is perfect for my purposes: a large illuminated chevron, to be zeroed at 50 yards, plus drop markings for 300-600 yards, the latter being just about the maximum effective range for 7.62×39. Rangefinding markings for each range are built into the reticle ACOG-style, where the crosshatch on the vertical line corresponding to a given range matches the width of an adult male’s shoulders at the same range. There’s also a rangefinder marking off to the side for standing height.

Other handy markings include dots for a 5mph crosswind at each range, and dots for leading a running target (at 8.6 mph, the generally-accepted speed for a man running with a rifle). The latter isn’t especially useful to me, since I don’t really hunt for anything, much less the most dangerous game. The former dots are nice to have, though; crosswind shooting comes up a lot, although I don’t expect it to do so too much with this rifle.

Final notes
There’s a canonical article on AR-15/7.62×39 reliability I want to address fully in a later post, but I do want to touch on reliability concerns and my results here. I went into this project with some trepidation on the reliable-functioning front, but emerged from Saturday’s range test with no remaining concerns: 40 rounds of slow fire while I was zeroing my scope and verifying that zero yielded no problems. Nor did 60 rounds of rapid fire, including some fast double taps, from magazines loaded to a full 30 rounds. 7.62×39 AR owners commonly cite two related pain points: cycling and feeding. For 7.62×39, you want a biggish gas port for the barrel length: at 0.087″, the port on the Faxon barrel in the ARK would yield a tremendously overgassed rifle for 5.56, but seems just about right for the ARK.

I’ve hit my about-1400-words target pretty handily with this first article. Stay tuned for the next one, in which I rag on the AR as a platform!

  1. I repeat this not because it’s necessarily strange (though granted, it is a little strange), but for SEO purposes. Hello, Googlebot!
  2. In defense of this rather bold claim, I present the 7.62 US cartridge (scroll down a bit), which was a subsonic 7.62×39 cartridge capped with a ~200-grain bullet intended to be used with the PBS-1 silencer on the AK-47 and AKM. Sound familiar? In any event, I intend to try some subsonic handloads and perhaps a suppressor of my own down the road.

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