7.62x39, By the Numbers
7.62x39 was designed in the Soviet Union in 1943 as an intermediate cartridge for the SKS carbine, the AK-47, and the RPD light machine gun, and it has been produced in greater volume than any other centerfire rifle cartridge since. It is a .311″ to .312″ bullet, typically 123 to 125 gr, on a sharply tapered case that feeds through a curved magazine at a maximum pressure of about 45,000 psi (SAAMI). The taper is what makes it run in a dirty AK; it is also what asks the most of an AR barrel’s chamber and feed ramps.
Ballistically it is a 123 gr bullet at about 2,350 fps from a 20″ barrel, which puts it alongside the .30-30 Winchester: roughly 1,500 ft-lb at the muzzle, deer-capable inside 200 yards, and far more energy inside 100 than a 5.56 with a bullet that does not depend on fragmentation. From 16″ expect about 100 fps less; from 10.5″ roughly 2,050 to 2,100 fps, which is still a supersonic 300 Blackout load’s worth of energy at a third of the price.
Faxon builds the 7.62x39 Duty Series barrels with a chamber and feed ramps cut for the tapered case, a 1:8 twist that stabilizes everything from 123 gr FMJ to 150 gr soft points, and a .750″ gas journal on the Gunner contour. The 16″ runs mid-length gas, which is unusual for the cartridge and the reason it cycles softly; the 10.5″ runs carbine gas for reliability with the lower-pressure steel-cased loads that make the cartridge economical.
Manufacturer-published factory data — 20″ test barrel where stated
| Load | Bullet | Muzzle velocity | Muzzle energy | Test barrel |
| Hornady BLACK | 123 gr SST | 2,350 fps | 1,508 ft-lb | 20″ |
| Hornady American Gunner | 123 gr HP Match | 2,350 fps | 1,508 ft-lb | 20″ |
| Federal American Eagle | 124 gr FMJ | 2,350 fps | 1,520 ft-lb | not stated |
Sources: Hornady and Federal product pages. Expect roughly 100 fps less from 16″ and 250–300 fps less from 10.5″; estimates, not Faxon chronograph figures.
Duty Series 7.62x39 Barrels
All 1:8 twist, 4150 CMV, QPQ nitride inside and out, 5/8x24 muzzle. Weights are nominal; prices are MSRP.
What You Need to Build It
A 7.62x39 bolt (the case head is .447″, larger than 5.56) and 7.62x39-specific magazines, whose curve follows the tapered case; the upper, barrel nut, buffer, and handguard are standard AR-15. Both barrels take a .750″ gas block on a 1.9″ journal, with a carbine-length gas tube on the 10.5″ and a mid-length tube on the 16″. A heavier hammer spring helps with the hard primers on some imported steel-cased ammunition. Muzzle is 5/8x24 with a .30-caliber bore; any .30-cal device or suppressor fits.
What Every Duty Series Barrel Shares
Duty Series is Faxon’s 4150 CMV line: the M4/M16 barrel alloy, button rifled, stress relieved, and salt-bath QPQ nitrided inside the bore and out, which hardens the surface while adding virtually nothing to it, roughly a tenth the width of a human hair, and leaves no plated layer to wear through. Every barrel is turned, crowned at 11°, chambered, 100% wet magnetic-particle inspected, and nitrided, then has its gas port drilled and reamed and its extension torqued to 150 ft-lb, pinned, and headspaced with a go/no-go gauge, and is laser-engraved with the Faxon shield, order number, and cartridge and twist, in Faxon’s Greater Cincinnati, Ohio plant. Faxon’s AR-15 and AR-10 barrels have been voted Favorite Aftermarket Barrel by Shooting Sports Retailer every year since 2022. All Duty Series barrels › All rifle barrels ›
Duty Series 7.62x39 FAQs
Does a 7.62x39 AR need a special bolt?
Yes. The 7.62x39 case head is .447″ against 5.56’s .378″, so it needs a bolt with a 7.62x39 bolt face. The carrier, upper, and barrel nut are standard. Choose a quality bolt; the larger bolt face leaves thinner lugs, and a well-made bolt is where the reliability of a 7.62x39 AR is decided.
What magazines work?
Magazines made for 7.62x39, which are curved to follow the tapered case. Standard 5.56 magazines will not feed it reliably. Ten- and thirty-round 7.62x39 AR magazines are widely available.
Does it run steel-cased ammunition?
Yes; steel-cased 7.62x39 is the reason the cartridge is cheap to shoot. Some of it has hard primers, and a heavier hammer spring or an enhanced firing pin solves light strikes. The barrel chamber and feed ramps are cut for the tapered case, and the nitride bore handles the bimetal jackets on some imported loads.
Why mid-length gas on the 16″?
Because the cartridge runs at lower pressure than 5.56 and a mid-length system, with its longer dwell, cycles it softly and cleanly on a standard buffer. The 10.5″ uses carbine gas for the same reason a 10.5″ 5.56 does: it is the proven short-barrel layout.
Ballistics are manufacturer-published figures from the test barrels stated; velocity estimates for other lengths are approximations, not Faxon chronograph data. Dimensions are from Faxon engineering prints; weights are nominal. Prices are MSRP. Check your state’s hunting regulations before choosing a cartridge.
