Build Thread Convert AR 7.62x39 to 6.8 SPC

TheGameMaster · Jul 9, 2019

I have a 7.62.x39 AR that I tried and tried for the life of me to get it to run Tulamo cheap stuff... it just did not like it. I tried everything. Got it to were it would run a half a mag before I'd get a fail to fire. Ejection and feeding are fine, but it's still a jam-o-matic. Its the ammo... heavy hammer spring, extended firing pin, etc. etc. etc. It eats brass ammo just fine. Doesn't matter what brass ammo I feed it, it's fine. But the cheap stuff, the point of it, it's annoying. So I gave up and got a real 7.62x39 gun (an SKS) and it's like night and day as far as shooting and accuracy. Love my SKS, am annoyed with my AK15. Its time to not let that platform go to waste... being a 270 Win. fan for hunting... it makes perfect sense to convert that bad boy into a 6.8 SPC. So, the question for the experts and experienced builders of non-standard calibers in the AR platform... What, at a bear bones cheap as cheap can be miniumum do I need to change out on my AR to make run 6.8 SPC? I hear the bolt carrier and pin will work, but not that actual bolt? I hear the 7.62x39 mags will work? What's the real skinny on it?

Thanks,

Rodney

osprey · Jul 9, 2019

I would keep the 7.62 x39 upper intact and build or buy a complete 6.8 spc upper as they both have a place. Yes the bolt carrier will work but I doubt the mags will but I have not tried them. If you build or buy a complete 6.8 upper, you will have two great calibers available with a push of two pins and some redundancy in parts. If you are serious about getting the 7.62x39 upper to run steel cased ammo, pm me, as I have built three that will eat steel ammo without a hiccup and have great accuracy as well.

TheGameMaster · Jul 9, 2019

I am also open to 6.5 Grendel and .277 Wolverine. I'm on the fence, but leaning 6.8SPC II, simply because I'm a old school 270 Win. user of days gone by. So I have the molds and sizer kit for dropping my own .277 pills for the 6.8 SPCII or the .277 Wolverine.

Because I have a 7.62 BCG in it, the .277 Wolverine would require a new bolt, barrel, and dies for reloading. But brass is easy to convert, and may be the cheaper option in the long run. Plus I can "steal" the bolt out of my .223 if need be when using it. So at a bear minimum it would just be a barrel and dies for .277 Wolverine.

The 6.5 Grendel would work with just a barrel swap and dies for reloading as well. And uses 7.62x39 converted brass. Not as cheap as the Wolverine for brass. However it would also require new molds and bullet sizing set for .265.

If all it would take is a new barrel and mags, then it sounds like 6.8 SPCII might be the way to go. As it is supposedly harder hitting than .277 Wolverine, but not as stable as 6.5 Grendel. However it would also require new brass. Which can be a big money hole. So I'm having second thoughts on 6.8 SPCII because of the brass issue.

So I'm leaning towards the .277 Wolverine the more I ponder it from a cost effectiveness standpoint. I am thinking the Wolverine may be cheaper in the long run, but the 6.8 SPCII may be better for hunting applications. But I do like the "cool" factor of the title "Wolverine". But even if it's cheaper in application, a reduction in effectiveness may not be worth the cost savings if the cost is not dropping your target.

I don't want to buy another upper. I'm cheap. As in CHEAP. All I want is for it to go bang when I pull the trigger, and hit a deer at 300 yards and drop it. If I go Elk or Moose hunting, I'll take my 270 Win with 140gr. Nosler Accubonds.

As to the 7.62x39 Upper, I was serious about it for two years of messing with it. Other than just building a new upper altogether or doing major work on it like lapping barrels or the like. Spending more money I don't have on it would just defeat the purpose of shooting cheap ammo. It's a money pit. I got an SKS that actually runs; no need for my "AK" upper; would rather Frankenstein it into something else. Very happy with the SKS. I could always put the barrel into another upper assembly if I ever feel the urge in the future, but don't want to spend the cash on another upper build right now.

Thanks,

Rodney

osprey · Jul 9, 2019

For about $70 and a the cost couple cpd mags if you don't already have them that 7.62x 39 upper would eat steel cased ammo like it was brass. Just have to have a barrel with the right chamber cut.

Famous No-Fail 7.62X39 AR15 Melonite Hbar Barrel

TheGameMaster · Jul 10, 2019

The more I read, the more I end up leaning towards the .277 Wolverine. They all have their strengths and weaknesses. To summerize what I've learned:

7.62x39 = cheap, cheap, super cheap, ammo and easy to re-load... and yes, you can reload that cheap steel too if you have a drill, L.E.Wilson Case guard, vise, and super glue. They run fine in my SKS. Not super accurate, not as powerful as 6.8 SPCII. Power drops fast after 100 yards. Probably the perfect pinking round, #2 for zombie Apocalypse.

6.8 SPCII = hardest hitting at 300 yards. Perfect for most hunting situations. Expensive to put together.

300BLK = best for SBR and use of supprossor. Good for under 200 yards. Similar to 30-30 pre-Leverrevolution/FTX (now 30-30 is nasty out to 400 yards; thanks Hornady & Hodgdons).

6.5 Grendel = reach out and touch someone. Can ring the bell at 800 yards. Carries more energy at 400 yards than 6.8, but less at 300 yards.

224 Valkyrie = More energy than 223, but loss of accuracy compared to 223.

22 Nosler = see above.

25-45 Sharps = see above. 25 cal. req. met in states where needed.

50 Baywulf / 458 SOCOM / Etc. = big, slow, under 100 yards, literally explodes game into squishy unusable bits.

.277 Wolverine = "why not have both?" Same performance to 6.8SPCII at 300 yards, same performance as 6.5 Grendel at 400 yards. Runs good suppressed subsonic like a 300 BLK. The trade off is you can't get a barrel longer than 16 inches in a 1:7 twist that will do both subsonic and supersonic. Longer barrels in 1:11 are for supersonic only. The 20 inch plus are the ones that hit the 6.5 Grendel equivalents at 400 yards. However, in my situation, if I am going to go do something that I know will be at 300 to 400 yards, I'll take my 270 Win bolt gun. So for what I "need" it for, it is sounding like the .277 Wolverine is going to be the more economical and balanced choice. As I can run it suppressed using the heavier 140gr. 270 pills for practice and messing around.

Or, I could just keep my 7.62x39 as is and not spend any money... my wife would like that option... hehehehe...

Thanks,

Rodney

turq · Jul 10, 2019

I have a friend that wants to sell a 6.8ll upper cheap,pm me.
PRI mags are the best.
Go to AR15Performance.com their barrels and bolts are the best, buy once.

TheGameMaster · Jul 12, 2019

Okay, 6.5 Grendel is out... yikes. Actual hunters are saying it's awful on white tail and hogs. Accuracy is only part of the equation. I don't like chasing game or having to put three or four shots in them to stop them. Looks like Wolverine is better than 6.5. But it appears that 7.62x39 and 6.8 are about equal in dropping things. Less than 300 its looking like accuracy isn't the key issue as much as damage.

6.5 Grendel

WLV

6.8

x39

Rodney

Boboclown · Jul 13, 2019

TheGameMaster said:
Okay, 6.5 Grendel is out... yikes. Actual hunters are saying it's awful on white tail and hogs. Accuracy is only part of the equation. I don't like chasing game or having to put three or four shots in them to stop them. Looks like Wolverine is better than 6.5. But it appears that 7.62x39 and 6.8 are about equal in dropping things. Less than 300 its looking like accuracy isn't the key issue as much as damage.

6.5 Grendel

WLV

6.8

x39

Rodney

To be fair, doesn't take much for an impressive gel test.

But, 6.5 grendel was meant to be better than .223, not 7.62x39.

osprey · Jul 16, 2019

In my eyes all the ar 15 available chamberings for hunting are limited in performance by the constraint of powder capacity. Out to 200 it would be hard to improve on your 7.62x39 although a 458 Socom is a hammer out to 150 yds or so. To me the grendel, the 6.8 spcII, the wolverine all about the same as far as capability on game due to the fact you can only propel suitable hunting bullets so fast with the smaller case capacities. Their are some specialty bullets that get quite spendy, but will expand at much lower velocities. If a guy was serious about stretching the range a bit they might have some application. Otherwise they are all about a 300 yard max proposition on deer. Don't believe all you hear and see about some of these chamberings as the info is frequently skewed one way or another. There is no reason the 6.5 grendel wouldn't be just as effective on game as the 6.8spc or the wolverine with the proper bullet choice. Also the 7.62x39 is a great 200 yard hunting cartridge but lacks the ballistics to stretch out to 300 yds unless some of the costly specialty bullets I mentioned are used. I have actually dialed in a specialty load for subsonic hunting with the 458 socom. It uses a Maker 500gr subsonic expanding bullet going 1050 fps. I have not shot it at game yet but I am confident it will work well at 100yds and under. I will be using it out of a tree stand. Good luck on your search.

TheGameMaster · Jul 18, 2019

All things being equal, looking at the numbers for a given bullet weight, its really close between the 7.62x39, 6.5 Grendel, .277 WLV, and 6.8 SPC.

The Grendel has higher BC over the WLV and SPC.

SPC has more terminal energy.

WLV has lower BC than Grendel, less energy than SPC, but cheap to reload once you buy the expensive custom dies for it. It's still a wildcat, not SAMMI approved, and MDWS is the only one making barrels and dies for it. You can, however, shoot it suppressed at under 100 yards like BLK with 1:7 barrels.

The drop after 100 yards on the 7.62x39 is ugly, in my experience owning both an AR and an SKS. The SKS is world's better with it's 20.5 inch barrel over my 16 inch AR, but it still drops like a rock after 100 yards and is way high at 25. It's a "minute of man" kind of caliber, which is what it was designed for. My AK buddies tell me to just zero it to 25 yards and hold over as needed, and don't shoot at anything over 100 yards. It's appeal is super cheap plinking ammo that you don't have to reload (it's the 9mm of the rifle world - 223 is the 45 of the rifle world for cheap ammo).

So I took the ol' 7.62x39 AR out of the dust bin in my safe, and discovered that I had not done the mag relief fix on the mags yet. So I did that, and turned the firing pin inside stop down .005 more while I was at it. And, magic. I had only 1 light strike and no failures to feed. I already installed an extra power hammer spring, and the PSA upper came with the extended firing pin in the BCG. It just wasn't quite long enough apparently. The jam-o-matic was now a nice rifle. I'll probably turn it down .001 more to try to get it a bit better. I did have a reset issue while I was out with it, but it turned out to be crud had settled on the trigger return spring and just need to be cleaned and oiled. Though I may need to put a heavier buffer in as it's now over running the buffer detent sometimes. I ran into that when I went to take the upper off and the buffer was sticking into the upper. I ran the charging handle and it went back in place. The detent is fine too. So my buffer must be too light, and that might be part of my problems with the light strikes as well, as it might not be lining up the hammer correctly? It's all cheap Anderson mil-spec stuff. I do have a spikes H3 from when I was messing with my 300BLK to get it to feed right. I fixed that a long time ago. But that might be too heavy.

So that leaves me with the emotional/shooter factor. Having decided that I've put too much blood into getting my 7.62x39 problem child to work right to get rid of it; plus having it's big older brother SKS now in the family, I don't want to convert it to 6.5 Grendel. Plus I don't have any 6.5 projectiles or molds and that would be another expense.

Then AAC had a sale on blemished upper receivers.. $49.99 with shipping ($39.99 sale price). I have one on my SBR I built, and the blemish was a small scratch on the underside of the forward assist roll pin hole.. a bit Alumablack and it looks pretty. So, stupid me, bought another one. Well, I can't just have a stripped upper receiver sitting around. I have to turn it into something... So that 80% I haven't done yet is also sitting there... long conversation with the wife... playing with budgets and so forth...

I already have all this stuff for .270 Winchester, and have had a love/hate relationship with that cartridge since I was 15. It kicks like mule in my Ruger M77 (pre-type 1)... It's down right painful to shoot compared to my M1 Garand. It only weighs 5 lbs. You suffer for each pull of the trigger. You pay for it in more ways then money. But since 90% of my .270 stuff will work in SPC or WLV, that narrows it down a lot on the emotional level. Something about having a "270" in my AR appeals to me on the emotional level.

All things being equal; I'd rather go with the SAMMI approved and industry supported 6.8 SPC II than the wildcat for a ground up build. So, my parts are in the mail. Now I need to work some overtime... like a lot of it... plus I have to get that lower done now... what a mess... I'm an idiot.

Peace,

Rodney

turq · Jul 19, 2019

I don't tell people.
My 6.8 ll s are ar15performance barreled and my friend's three 6 in total; ALL are 1/2"
5 shots at 100yrds.
We're each over 60 so eyesight is on a downturn.
16" to 22" AR 15s forearms MUST be less than $100, no $270 miracles.