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BeatTheTunaUp

7.62x39 AR Pistol build

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I went to the Texas International Firearms Festival and shot quite a few AR pistols in different calibers suppressed and non with the Sig brace.  Few weeks later of some back and forth, I've decided to build one for myself in 7.62x39.  I"m not a big fan of 5.56 out of the shorter barrels.

 

I've bought a Phase 5 tactical Pistol lower and their Hex2 buffer tube kit along with the SBX brace.  

I plan on using a 10.5 barrel but if there are good arguments for a 7.5, I"m welcome for someone to sell me on it.

 

I'm also looking at lower parts kits.  Right now, the Palmetto State Armory kit with the ACT trigger on sale is my probable buy, but I"m an AR newb.  Any advice on lower kits and/or triggers would be awesome.  

 

I'll post pics as everything shows up and it comes together.

 

HexOne-C_Main.jpg

 

 

And here's the old sb15 brace mounted to their buffer tube.

Hex2_support3.jpg

Edited by BeatTheTunaUp

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I just finished this.  Pretty basic build.  10.5" barrel.  I can't see going shorter with the 5.56. 

 

Got the lpk from KAK.  Standard milspec stuff.  The trigger isn't bad.  It will get better with use.

 

Next is the 300bo pistol.  I considered a x39 but I have that covered.  And if I was going to go x39 pistol I'd just get the 556xi pistol that uses the proper mags.

 

They tell you to use talc on the brace but I didn't want to deal with the mess.  It just took some elbow grease to get it on.  The KAK tube is made for the brace and it's tight.  Not going anywhere.  Don't know about the hex tube.

 

post-4831-0-29758000-1416453104_thumb.jpg

Edited by Darth Saigus
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That's pretty slick looking Saigus big_smile.gif   That 10" barrel looks perfect.  I found what I guess is a decent deal for a 10" barrel with free floating quad rail, 30rd mag, 5/8x24 threads so I can swap breaks with my S308, bcg and charging handle for $425 shipped.  Probably going to wait though. Not in much of a hurry.   The Hex2 is their 2nd version made of 7075 and the hex shape matches the Sig brace.  It was designed for it like the KAK was. 

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I am also considering a 7.62x39 pistol upper build.  7.5" barrel with a Noveske KX3.  Kind of matching the 5.56 pistol I already have.  I've found some decently priced parts and even a melonite 7.5" barrel for it. 

Looking forward to seeing what you do with yours.

 

Palmetto State Armory has good stuff.  I haven't done this to mine, but it does as much as I want it to with no issues. 

https://www.youtube.com/watch?v=g2rG8xXfDbg

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I've got another question that I can't seem to find the answer to. 

 

Can I put a rifle upper on my pistol lower while keeping the pistol tube on it? 

I want a 16-18" 5.56 upper.  All I can seem to find on forum discussions are about short barrels on rifle lowers and such but nothing about rifle upper on a pistol configed lower. 

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Very nice! Only thing I would add is upgrade the trigger. I hate mil spec AR triggers....pick any brand you want just get rid of the one that came with the lower parts kit.

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Thanks! It was my first AR build and my first AR to own. Gotta say, I enjoyed assembling it and it's got me looking at building a rifle lower. It's like Lego Technic for adults.   It's the ACT trigger from ALG defense.  The trigger has a nickel-boron coating and the hammer has a nickel-teflon coating.  It's pretty smooth and crisp.  It's a lot better than my MP15-22.  I've only tried to fire it once and I got a light primer strike.  I got the enhanced firing pin, so I'm thinking a new stronger hammer spring, or maybe a heavier hammer.  But then I'd loose the coated hammer that makes the pull nice.   

 

Any tips?

Edited by BeatTheTunaUp

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Palmetto State Armory has good stuff.  I haven't done this to mine, but it does as much as I want it to with no issues. 

 

Yes they do....most of their parts are machined at the FNH plant across town.

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I was in the process of deciding between a BCM 11.5 and an LMT 10.5 for my build. Looks like the PSA 10.5 is a viable option now, too. 

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Thanks! It was my first AR build and my first AR to own. Gotta say, I enjoyed assembling it and it's got me looking at building a rifle lower. It's like Lego Technic for adults.   It's the ACT trigger from ALG defense.  The trigger has a nickel-boron coating and the hammer has a nickel-teflon coating.  It's pretty smooth and crisp.  It's a lot better than my MP15-22.  I've only tried to fire it once and I got a light primer strike.  I got the enhanced firing pin, so I'm thinking a new stronger hammer spring, or maybe a heavier hammer.  But then I'd loose the coated hammer that makes the pull nice.   

 

Any tips?

That trigger will work fine...it didn't look mil spec but it got blurry when I tried to take a closer look. I have a few ARs but none chambered in x39. If it was 556 I would say try some non mil spec rounds...some times the mil spec primers are a little harder...for the first 100rds and then back to mil spec...not sure if that could be an issue with x39. They are very additive to build...just be careful next thing you know you will have a half dozen complete rifles and a couple stripped lowers in the safe and a drawer full of parts...that is what happened to me...I found myself build one for a scope I bought a couple weeks ago....lol

Currently my buddies and I are trying to see who can build the cheapest one, only rule is no polymer..currently, before Black Friday, the leader in the clubhouse is $876. As soon as PSA has another batch of blemished uppers I may be able to beat that...LOL

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I found an upper for $270 with bcg and a blem lower for $49.  Cheap parts kit for $39 and tube/stock.  Could build a cheap rifle for sure.     The pistol added up quick, but nothing is stock mil spec except the lower parts kit.  

 

My ffl said he has a bull barrel rifle upper that I can put on my pistol just to see how bad the balance gets.    Thinking of getting a 16" pencil barrel in .556  to have another caliber option just in case.  That's if it's not to front heavy.

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I think I fixed my light primer strike issue.  I took a closer look at the hammer spring, and it was backwards from the supplier.  I popped the pin and flipped the spring around, and there is a lot more preload on the hammer now and trigger pull is a little higher but still clean.  I also noticed that the M4 feed ramps look like they're for the 556.  I need to widen them for the 7.62.  I've ported a few sets of heads before, so I should be able to tackle that. I also noticed that on the ASC mags,that while unloading by hand, the rim of the cartridge will snag on some dimples.  Need to smooth those out too.  Hopefully it'll run pretty good after all of that.

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Cobratacsystems has a 7.5' melonite/nitride barrel and melonite/nitride BCG for the 7.62x39 now.  I'm probably going to use those when I start building mine. 

What Barrel and BCG did you use for yours?

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I used a Hardend Arms upper with their bcg and enhanced firing pin.  I don't have a lot of experience in AR's to compare, but it seems nice.  Fit with my lower is rock solid tight.  The gas block is pinned to the barrel, melonite 10.5 barrel with free float quad rail.  They only thing I have to do is widen the M4 feed ramps for the .30 cal bullet.

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So I went shooting yesterday and broke the hymen f0ckers.gif   It shot pretty soft, but is very LOUD.   

The only issues I was having, was a FTE(eject) and magazines would bind if loaded to 30rnds.  I already ordered the BCG extractor spring upgrade to hopefully fix the ejection issue.  Might look into some ejector springs too.

 

I also noticed that the bullets seemed to be tumbling at 25yds.   Was shooting 123gr fmj that only measured .309 so that might be the problem.  Barrel is 10.5 inch with 1/10 twist and has a big muzzle brake with two small ports on top to go with the large side vents.  I didn't see any bullet strikes on the brake, but I could see how gasses leaving 3 sides might cause an uneven push at the end.

 

Another issue was, that when I loaded one of my ASC 30rd mags up to 30rds, the follower seemed to get stuck.  The rounds up top got loose and I was able to shake them out of the mag.  I beat the mag on the bench a little and the follower freed up.   Is there anything I can do to improve the magazine, or do I just need to wear it in?

 

Any ideas?

Edited by BeatTheTunaUp

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The issue you described above is why I don't have a AR chambered in x39...I have friends that do and they all have issues with the mag feeding when fully loaded. If there is a solution out there I am not aware of it...they do get a little better with use but for some reason the curved mag feeding into an ar just doesn't seem to work. I would love for someone to post up a solution and prove me wrong as that is the only caliber of AR I don't have and I would like one.

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I would love for someone to post up a solution and prove me wrong as that is the only caliber of AR I don't have and I would like one.

 

 

Make your AR use AK mags.

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Aimsurplus has C-Products Defense 28 round magazines that I've read work very well.  I know their 9mm colt pattern mags, with the red follower, work like a charm.

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