"new" 308 ar setup. 308x39 American

[bld451]

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")

[MegademiC]

So is this a .308 bore or .311 bore?

[bld451]

.308 bore and .308 bullets.

[bld451]

To be clear, we fireform cheap 7.62 (.311) factory brass ammo (right now Geco 123 fmj reloadable brass case stuff is .40 cents/rd) to obtain brass, then load it with 308 bullets.
Our chamber is designed specifically to do this . We are waiting on full length dies, and are making do with a neck sizer I made for the data i listed above.

[Lefty223]

I dunnoh ... my -39mm Russian AR is getting better accuracy results using Golden Tiger, Barnual, Seiler & Beilot and Brown Bear bulk offerings, Brown Bear soft-points shooting sub-MOA @ 200-yards. Using PMC premium hunting soft-points its even better.

Sounds like a fun project! FWIW I added a JP Enterprises adjustable gas port and that, along with the linear design inherent in the Stoner design, rings out all the potential in existing -39mm Russian offerings.

But I like your idea, as I shoot my -39mm AR 3-5X more than in 5.56mm. I am just surprised your groups weren't better ...

[constructor]

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")

There are some similar cartridges that have been around for 5-10years with the same performance.
30 American-pretty much a 30 Herrett stretched .050" made from 6.8 brass -offered by BHW
30 Herrett-made from 6.8 brass and uses 30 Herrett dies-offered by AR Performance
30 HRT -30 Herrett made from 6.8 brass offered by Teppo Jutsu
30 Gremlin -30 cal Grendel -Closest to yours. The AMU have used it for 3 gun.
30 ARK-same as a 30Gremlin
30ARX-Whitleys copy of the AMU
Several people have made 7.62x39s that use .308 bullets in 308 barrels.

Your 150gr loads seem fast- I'm shooting 130gr bullets at 2600 out of 16" barrels in the 30 Herrett.

[bld451]

Indeed there are several very similar cartridges. Some pretty good stuff out there. It is a great time to be a shooter. We liked some of the ballistics we saw, but I could not believe the 7.62x39 AI had not been written up much at all in an AR. We are shooters who handload, but with limited time for our preferred recreation, we didn't want to be buying .80C/ea brass (when we could find it), annealing, neck expanding, trimming, then loading a .20c bullet to fireform, etc. The others don't all require every processing step I mentioned, but we liked the idea of having a case of quality ammo shipped to our door for <.60C/ea, and going shooting. (Just ordered some Geco brass cased stuff for testing at .38/rd, and Fiocchi, PPU, Win, Federal, PMC are available for a little more) Brass case 7.62x39 is available most any town with more than one good sporting goods store. With factory 7.62x39 ammo off the shelf and ready to shoot in our gun, a trip to the range for some drills or to the dog town gets us started with brass ready to go, and we're shooting, not scouring the web for sub-$1.00 brass, expanding/trimming, etc. Of course it is not all cost, as the testing we have done has cost us a lot more than 1,000 rds of Lapua brass. We are having to neck size with a homemade die now until our full length dies are in, but we're getting good results at that.
We are having fun with it and doing it our way. I think there are a lot of little advantages the way we are doing it. (reduced bolt thrust due to less taper, better feeding out of a standard ar15 magwell, efficient case, easy case forming, emergency ammo availability, etc) It is not a 308. It is not optimized for subs. (our Blackouts are better for that) It is a pretty darn good medium game cartridge that is a barrel/bolt swap into a favorite AR, and easy to load for, with components that are available and that work.
For someone who is set up for SPC, this option may not make sense. Heck, if somebody thinks it is boring, it may not make sense for them, but we like it and it seems to be living up to our expectations. We'll follow up for those interested.

[SomeOtherGuy]

1) What magazines are you using? Do they feed reliably when fully loaded (25+ rounds)?

2) What kind of bolt life and margin of strength do you see? I was under the impression bolt durability was a major issue with 6.5G and your cartridge seems likely to impose similar stress on the bolt.

[bld451]

We have been using ASC and C-Products Defense Grendel magazines. Unfortunately in Colorado, we don't have ready access to the AA 25 round variety. We had some 7.62x39 30 round C-Products mags that work fine with fireforming, but after the taper is gone, they don't play well unless you load 10-12 or less (using the straight section of that magazine). The ASC and C-products 5, 7, 10 and 15's seem to be working fine. In fact, 7.62x39 mags 10 rounds or less have been working well also. The ASC 15 that I have been using is a little tight with the last round in the mag, but works great.

As far as bolt strength, we will have to see how it works out. I see some advantage with less bolt thrust due to the relatively straight body taper, but we are giving back some of that with loading back up to pressures in the 50-55K range. I think part of the problem with the Grendel bolt scenario (other than obviously less metal supporting the lugs) is folks loading it hot. I have not owned one, so that is pure speculation on my part, but I think with a newer good bolt and following best reloading practices, they should last.