Anyone running a 7.62x39? I seen upper for sale some where .  A 7.5" upper.  I 've heard people have had issues with magazines feeding issues.

Is that round any good out the short barrels?

Yes, as good, if not better than 300BO.

Picked up a complete carbine upper in this caliber from Palmetto State Armory in the AR platform. Mounted it to one of my 80% lowers with a Primary Arms red dot and Magpul BUIS. Runs like a top with CPD 30 round magazines. Use ASC mags as well.  Really fun to shoot and pretty damn accurate at 100 yards using brown bear ammo.

X39 has gotten a lot more popular in AR rifles and pistols lately. The biggest issue is the bolt lugs breaking off because the base of the X39 cartridge is larger reducing the material and strength of the bolt head. LMT makes a bolt out of stronger steel which holds up. I've put a 7.5" upper together and just waiting to save enough for an LMT bolt to finish it.  

I have a 7.5 pistol and it is the most fun ever. Shoots like a laser out to 150. Cason Eng. or LMT bolts. 4 times the costs of the others but they actually work. Mine is LMT. (after 3 broken pos's. Slow learner)

Thank you! Ill look into lmt.

I have one in an 11.5" barrel that I'm still working the kinks out of.  Build went together with no real issues.  Running it has been the problem.  I had a stock strength hammer spring.  Changed to a wolf extra power one.  Seems to have cleared most of those problems up.  Now I'm having feeding issues.  Which seems as though the round is coming outta the mag and getting stuck on the feed ramp of the barrel.  Going to massage those sometime in the coming weeks.  Wont be able to test for a while since the range is closed due to hunting season.  Its a fun gun to shoot.  And rounds are cheaper so far.

LMT is awesome and the only civ-side rifles I almost assume to trust. Everyone else I've ever tried has failed me.

But I wouldn't rely on extra strong steel to prevent a breakage. That's just cutting it too close for me. As long as the CMMG Mutants prove they are good to go, that's what I'd go with. That said, I'd be a lot happier if it was LMT instead of CMMG just probably being the next one to fail me.

Run a 16" from Hardened Arms, and the only issues have been self-inflicted.  10 rd. and 30 rd. CPD mags from Brownells and shoot.

In short barrels, I'd say it is a proven round. The soviets have been useing krinks forever.
As for mags: I have tried CProducts and ASC. CProducts works 100%. ASC sucked, had to lube the inside and it seems to work for now.

I saw that palmetto had the 7.62x39 upper on sale and I was thinking about them but the only draw back is the magazines. some that work and some that don't just like the asc magazines I head a lot good things about them and also bad things.

I have a 7.5" with a D&H mag and love it.

A number of 7.62x39 platforms were having issues because of magazines but C Products Defense solved all of that.   C Products Defense is making the only 7.62x39 magazines that actually work.  As reported at NASGW last month, a few firearm manufacturers are saying that they are going to get back into making a 7.62x39 platform again because they now have a viable magazine thanks to C Products Defense. Firearm manufacturers have become more and more picky about the mags they send out with their rifles because they know a bad magazine can ruin the reputation of their firearm. If you have a 7.62x39 gun you want a C Products Defense magazine.

Recently a major firearm manufacturer test-fired over 100,000 rounds through C Products Defense magazines with ZERO failures, no other magazine even came close. They have been busy redesigning all of the AR magazines at C Products Defense with a caliber-specific geometry and a proprietary coating which increases lubricity.   The C Products Defense 7.62x39 magazine will solve all of your problems.   Website: www.CPDmags.com

They are next on my list, my ASC ones are not 100%

You must work for the company. You only have 2 posts, which are almost identical and sound like a sales pitch.

Company man or not, CPDs are the only reliable mags I've found to be reliable. ASCs were hit and miss.

What he said.
I have been using 6 latest Gen CPD 30rd mags and 2 ASC 30rd mags and I like the CPD's quite a bit better.
Have around 2500 rounds just using these 8 mags equally and the CPD's are better.
CPD's are Better feeding, easier to load, otherwise they are equal with ASC IMHO.

I don't have a problem with the magazines themselves, just with the deceptive way the company is trying to promote them.

I have both C Product and ASC mags.  ASC mags' feed lips change the angle of the round to be higher so it helps with feed reliability, but the coating they use on the mags is garbage.  I've only run about 100 rounds through one of my 20 round ASC mags and it already looks like it's had years of use.  The C Product mags' feed lips leaves the round sitting at a more horizontal angle, but the front of the mag is lower so the round doesn't hang up there.  The coating on the C Procuct mag also seems to be superior.  My 30 rounder has seen about 90 rounds and still seems in decent shape with only minor wear.  Both mags have performed flawlessly for me though.

I have one and haven't had any issues with the D&H tactical magazine.

will it shoot subsonic?