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How interested are you in this slightly different but not new concept?

  • Not at all. That's a dumb idea.

    Votes: 1 12.5%
  • Not interested, but have fun!

    Votes: 3 37.5%
  • Keep us posted.

    Votes: 4 50.0%
  • I want one!

    Votes: 0 0.0%
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Discussion Starter #1 (Edited)
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 last 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"........ Questions, suggestions and trolls welcome. :)
 

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Sounds like an interesting cartridge. However, I can see where it might cause issues like folks shooting a regular 7.62 bullet (.311") in a .308" bore. Chamber pressure might be a bit too high firing a .311" in a .308" bore. Ruger's Model 77 MKII was once chambered in 7.62 X 39 m/m but their bore was a .3095" so one could use either a .308" or .311" bullets.

Edited: Maybe if renaming the cartridge from .308 X 39 m/m to .308 Short, it would avoid confusion. Frank Barns developed a shorten .308 cartridges years ago called: .308 X 1.5" Barns.
 

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There have been a LOT of cartridges designed that go into the AR15. The problem is the restrictions on size in about every dimension. As well as cartridge taper. The 7.62x39 does not work so well with the AR15 mag well. In an AK it's a rock and lock type mag that seats outside the receiver. The AR15 has a mag well that the magazine sits in.

Essentially you are still using a wildcat. Davers pointed out some importance with the difference in bores. Also note that the case head of 7.6x39 is quite large for an AR15 bolt and you will sacrifice a lot of material and strength there. The 7.62x39 and 6.5 Grendel are known for breaking bolts from time to time. Not enough to worry me in a rifle meant for hunting only though.

I would have gone with a 6.8spc based round. Since I've already got lots of 6.8 stuff. The 6.8spc cartridge is well proven in the AR15 now, and you can buy a factory barrel for it... the "30 American" from BHW...


But, I do hope it works out well for you. It sounds like it will make a good hunting cartridge that you can reload.

There are a lot better factory options in the 6.5-6.8mm realm for AR15's than there are the 7.62/.308
 

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The 30 Remington AR solves the problem of wanting a bigger 30-caliber than a 300 Blackout, while still using the AR-15 platform.

How easy is it to find Boxer primed 7.62x39?
 

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Discussion Starter #5
Thanks for the responses.

Davers, I have seen the 1.5 Barnes. Neat cartridge, but if we had a 308 bolt face, we would probably go with a full 308 in an AR10. The Bore size was an issue I thought about a lot. I ended up with what I think is a best fit in the neck/throat area that would safely fire any SAAMI max dimension 7.62x39 cartridge while still being close enough to give an accurate release with a 308 bullet. a .310 bullet will work here as long as the neck/throat are ok, and .310's are not seated out to the rifling. We have fired two guns so far with this chamber and have not seen any evidence of pressure. Not every brand, mind you, but a representative sample of what is available. Steel case stuff split about 20% of the time. I expected worse, but any rupture is not acceptable. Brass cased ammo only, and specifically designed to reload with 308 diameter bullets.

Trent, we had a 150 grain bullet as one criteria for this cartridge, and 6.5/6.8 wouldn't get us there. Our chamber has a body taper very similar to a Grendel, and feeds very well out of either x39 mags or Grendel mags. This is a wildcat for sure, and we intend for it to be a handloader's proposition at this point. As for bolts, I hear you about the weaker lugs. We are hoping reduced bolt thrust from the small body taper will alleviate some of that stress. Probably going to give back any advantage there with slightly increased pressures, but it is intended as a hunting gun, so a 20,000 rd torture test is not in the works. We hope to have thousands of rounds downrange with these someday soon, so maybe we can update the situation. We'll see how they do. Have you hunted with your 6.8's? Looks like a neat cartridge.

Broom, We thought about the 30 Rem AR, but the barrel extension is proprietary and does not fit a standard AR15. We were looking to make this a simple barrel/bolt swap. As for ammo, there is x39 steel everywhere, but we were able to find some brass boxer primed stuff on the shelf with a little looking around. Winchester, PPC, etc seems to run the gamut locally from fairly reasonable to 1.00/rd or so. Online we have been finding Geko, PPU and Fiocchi for around or slightly less than .50/rd. I'm thinking if we ever have another shortage, I'll be able to find 7.62x39 more easily than any of the other 30 cal AR rounds. Maybe not, but methinks so.

Thanks for the thoughts. Keep 'em coming.




 

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Winchester 7.62x39 brass cased ammo can be found at my local Walmart pretty easily. There are a few other brands as well. I used to shoot a lot of 7.62x39 and 5.45x39. Good luck finding any brass cases 5.45x39. As far as I know none is made! But you shouldn't have too much trouble finding 7.62x39 brass cases.

As far as the 6.8... there is a lot of info out there on the cartridge. The cartridge can have a lot of confusion surrounding it too. I'll start off with yes, it makes a great medium game and predator cartridge. DMSBandit on here has taken quite a bit of game with his if I remember correctly. I've only used it on coyotes, rabbits, prarie dogs, and 1 pig... worked as good as anything else I've used. No magic to it, it's just one of millions of different cartridges.

The 6.8 offers a good increase in performance if you reload as well. You will notice the talk of "6.8spc vs 6.8spcII".. so essentially most manufacturers use the SPCII chamber which allows for a good little bump in performance with hotter handloads. But no factory ammunition is made to SPC2 spec. I think the SSA "combat loads" may be SPCII but I'm not entirely sure. Point is, handloads if you want the best performance. Factory ammo is not bad though and works well. The only downside is you're limited to 120gr pills in 6.8/.270. There is data for 130gr but they won't fit in a magazine and feed. There is talk of some new aluminum or steel magazines being made for the LWRC SIX8 rifle (proprietary AR15 designed specifically around 6.8spcII) that will allow the longer COAL with 130gr pills. I'm surprised there hasn't been more work done with the Six8 receiver sets that LWRC was selling. Essentially it's just an AR15ever so slightly sized up to work in perfect sync with the slightly larger cartridge. Very under utilized wildcat possibilities if you asked me! I think a re barreled one in a wildcat 6.8 necked up to 7.62 would be cool. Or maybe one necked down to .223/5.56 cal to get some higher velocity in a varmint build? I would want the mags that allowed a slightly longer COAL though.


On the very tender subject of 6.8spc vs 6.5 Grendel... they're both intermediate cartridges and they actually are very similar all the way out to 450+ or so yards. Which is fine for me. If you're shooting at those ranges you brought the wrong rifle and cartridge. Take your pick of 6.5 or 6.8. I think a lot of the bickering between people who own the cartridges is because they're so similar and everyone wants to be the wiener!

Although I'm not interested in another wildcat personaly, I would like to know how this works out for you and what kind of performance you get from it!
 

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The .308x39 isn't something I'm interested in but not everyone is the same. Still liked hearing how it turning out and problems overcame.
 

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Discussion Starter #8
Quick report from the range. The 20" barrel we re-chambered went out with a slightly larger gas port today. Seemed to work fine with the brass cased ammo and handloads, but steel cases still didn't cycle. OK since that is not the intent, but we want to test it because folks will want to know. No split cases today. Go figure. Since it was originally a 7.62x39 and has a .310 bore, we elected to pull some 123 gr bullets from some factory x39 ammo and load them. We have observed about a 60 fps drop in velocity when the 308's are fired in a .310 bore. No accuracy work, but the chronograph showed us over 2600 pretty comfortably. Started to see some evidence of pressure nearer 2700, but only one powder tried. Short day, but good info. More to come.
 

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Guess you lost me. Thought the rifles were set up to use .308 diameter bullets. Is the bore still .310?
 

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What interest I would have in a 308x39 AI is predicated entirely on shooting .308" bullets in a .308" bore. I have no interest in this if I'm forced to choose between shooting undersized bullets or selecting from the relatively limited number of .310" bullets.
 
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Discussion Starter #11
The 310 bore barrel was re-chambered as a test barrel. It is giving us some info on apples to apples comparison between the two cases (before and after conversion). It was an option for a 20 onch barrel that would get us shooting the cartridge last week. We are going to have to turn our final barrels from a blank to get the right combination of bore size, length and port size. A simple re-chamber of a 300 blk will be fine if you want a 16" barrel and have an adjustable gas block but 20 inches isn't readily available and the ports are too big. This is an intermediate step to see what we can get with 125 class bullets while we wait for our barrel blanks. 308 is the intent. We will post developments as we can and hopefully not confuse the issue.
 

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What interest I would have in a 308x39 AI is predicated entirely on shooting .308" bullets in a .308" bore. I have no interest in this if I'm forced to choose between shooting undersized bullets or selecting from the relatively limited number of .310" bullets.
If I wanted to duplicate 7.62 X 39 m/m or even .30-30 Winchester performance/ballistics using 125 to 150 grain bullets; I would simply reduce the loads in my .308 rifle, to their ballistic levels. I tried shooting .308" bullets in my CZ-527 carbine, which has a .311" bore diameter but the accuracy was not that good, as if using .310" sized bullets. The cases even ejected covered with residue, around the neck & shoulder area, from the burning powder.:)
 

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Discussion Starter #13
Yeah, we have no interest in shooting 308's in a 310 bore either. We noticed sooty cases when fire forming in both guns but not so much with reloads. 308 win is such a versatile cartridge sometimes I wonder why we mess with things so much. Then I have an idea. Then..... well..... here we are. We are on our way to having some real deal data. I suspect it will be on par with the Arrow, Major, ARX, Hrt, etc, but we want to gather actuals with the bullets, brass, barrels we will be using. Just can't get all the parts together immediately. On our way, though. Eventually we'll have a 308 AR15 conversion that performs well, uses widely available ammo for cases and is easy to work with.
 

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I'll be interested when you've done some testing with a .308" barrel. As wildcats go, this one makes as much sense as any, and more then most, in some ways. :)
 

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Doesn't sound to me that it would gain anything over the .30 HRT. 2850 fps out of a 16" and over 3000 fps out of a 24" barrel AND based on the 6.8 SPC. It works in the AR platform, no problems with using 6.8 mags, and better than MOA accuracy. It's also a simple rechamber job from a .300 BO to a .30 HRT.
 
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Discussion Starter #16 (Edited)
Maybe not enough gain in velocity not to mention, but maybe so. We'll find out after we have barrels ready in a week or two.

Depends on how you want to obtain brass to load. Some like to trim, size, load and fireform. With ours, we just buy brass cased boxer primed 7.62x39 ammo at (right now) about 60 cents a round, and go shoot prairie dogs or do some training, pick up our brass and go load for the 308x39. I think they will not even require trimming for a while.

Re-chamber is the same as the HRT. Just a little more metal to remove. Cleans up a B.O. chamber just fine. Gas is an issue with both, I think, as you'll likely not find a B.O. with a port location longer than carbine length. They tend to be big out there, too, and you will be overgassed either way. Adjustable gas tubes/ports are a great thing.

After talking about it for a while, we were surprised about how little has been documented about this cartridge in an AR. I am quite sure it has been done, and possibly quite a while ago, considering the amount of wildcatting that has gone on with the x39. We just could not find a whole lot out there on the 'net.

Not everybody's cup of tea,(especially if you are set up for SPC already) but we think it is interesting and has potential. Thanks for the input.

B
 

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Not everybody's cup of tea,(especially if you are set up for SPC already) but we think it is interesting and has potential. Thanks for the input.

B
I think the headwind you're going to run into is this: The 300 BO, 30 Remington AR, 30 HRT, and your 308x39 are all marginal for hunting thin-skinned medium game animals. They all have relatively few merits, the principle one being that they will run through an AR, or "MSR", if you like. The reality is they are all inferior to the stately old 30/30, have limited effective range (for hunting) and are better suited to either banging away at steel targets, or to defend home and country. They are best used as "plinker" cartridges, to be frank.

None of them are truly GOOD choices for hunting, so they are all more or less the same, in other respects. The 300BO has attained some popularity because it can be suppressed and shot sub-sonic, with heavy-for-caliber bullets. Why that appeals to some is beyond me.
 

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Feeding issues with the 7.62x39 ? Really ? I put together an AR-39 using an AR Stoner upper. Never had any issues with feeding. Using only AR Stoner mags. Never tried any other. Only issue I did have was the firing pin protrusion needed to be improved from the factory .035 to .042 to light off the surplus AK ammo. Lots of this stuff uses pistol depth primers.. Want a heavier bullet ? Load em yourself with 150 grain .308 bullets. 150's actually shot better in my AK than the surplus stuff. Lots of load info out there for this.
 

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Discussion Starter #19
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.

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 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")
 
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