So a friend was wanting a "little more" than his 300 blackout would give with a 150 grain bullet and we started tossing around ideas. He wanted 30 cal but didn't want to go AR-10. So there are several options, but each has their issue. One uses a proprietary case and loaded ammo is available, but costs about $1.50 each. Standard 7.62x39 seems to have some feeding issues and a fairly sparse selection of good hunting bullets. Wilson has one that seems to beat the blackout, but not by much, and the ammo cost is an issue again (this will sound funny later). There are several wildcats that have been used successfully, but we didn't want to trim, size, blow out shoulders and then load a .25C bullet in .80C brass to fireform, etc. I suggested a 7.62x39 Ackley improved, and kind of chuckled inside. Well, in talking over the Ackley treatment with him, I started to convince myself that it might actually be a good fit for an AR15. As it turns out, he thought so too. Able to fire readily available and cheap (for now, at least) ammo which you could reload to somewhat better performance, shoot a great variety of .308 cal bullets in a .308 bore, case stretch would be greatly reduced (no trimming for a while), new body taper feeds great out of available and cheap Grendel and standard 7.62x39 magazines, body taper reduces bolt thrust and wear on the weaker bolt, new reamer cleans up 300 BLK chambers. We had to investigate. I felt funny re-visiting this, as the russian cartridge has been one of the most altered cases in shooting history, and what we were going to do was old news. However, there was not a whole lot on the web about anyone using it in an AR.... so..... We came up with a design, ordered a reamer and we're off!

Here we are in the shop a few weeks ago Saturday chambering the second rifle and prepping for a range day with our new 308x39 American AR's. I guess we were really just itching for a project. (slightly more expensive than a LOT of Grendel or Arrow brass...)

As it turns out, I think it will be as good as we were hoping it would be. We had an issue with small gas port size on the rifle, and ended up single loading it to fire factory x39 ammo, but accuracy was as good as the original chamber (2" at 100) and we only lost about 60 FPS fireforming. The carbine was a little overgassed as it was a blackout in its previous life and had a big port in the carbine location, but it worked great! Even with the blunt round nose soft point PPU brass case ammo, it fed from C-products 7.62x39 30 rd magazines over 90%. We don't have dies yet, so I made a neck sizer and we took loading gear to the range so we could at least fire some reloads. We ran out of daylight before we could reach the potential of the round, but with pointed .308 SP's in our neck sized cases it was almost 100% function and we still have some room to grow with charges. We'll see what it can do for velocity next time out. Pretty fun project.

Anyone else got a similar project going? We may yet find out why this hasn't been a "thing"..


Memorial Day Update:

Got to do a little testing Monday AM with the new 24" barrel. .308 caliber with .111 port at the rifle position. We are likely going to end up with a 20" but wanted to see real numbers on the chrony, and since the blank was a 25", why not? Hopefully soon we will have apples to apples comparisons with 24, 22, 20, 18 and 16 lengths with same loads. We're thinking we might only lose maybe 10-15 fps per inch when we start cutting the barrel.

The .111 port was still a little small in the longer gas system, but it's getting there. Going slow with opening the port. We need to balance the need to cycle the factory ammo that will have lower pressures because of the chamber size and the desire not to over-gas the higher pressure reloads. Might end up with carbine gas...

I tested a limited number of loads because there was limited time to prep and only an hour or so to shoot. RL-7 and H335 were the powders loaded for this trip. I'm not going to publish charge weights at this point, but velocities were decent without any signs of pressure and half shot 2" or better. Might be more room to work, but I need to spend a little more time with it. These were averages of three shot strings per charge weight to get an idea, and I hope to be a little more deliberate for accuracy next time. I apologize for the abbreviated data, but it's what I have right now.

110 Nosler Varmageddon w/ H335 = 2635 FPS avg next to least accurate load (2-4")

150 Sierra Gameking SPBT W/ H335 = 2485 FPS avg least accurate load (3-4")

150 Sierra Gameking SPBT W/ RL-7 = 2500 FPS avg Most accurate load (.75-1.75")

165 Hornady FB SP W/ RL-7 = 2290 FPS avg Second most accurate load (1.5-1.75")