Does anyone know if a 7.62x39 upper will cause more stress on the pin holes of a full auto lower than sticking with the 556 round?

If it's good to go and wont egg out the pin holes any time soon.  Does anyone have a 7.62x39 upper they recommend, or a barrel?

Ok i'm going to pack as many questions as possible into my post so I dont spam around here.  I've got 556 and 22lr uppers, are there any other uppers for a transferable I should try out?  I'm staying away from 9mm and have a 300 blackout upper I have not shot in the past 6 year and no 300 blackout ammo.

Thanks,

Great 7.62x39 upper: PWS Mod 1 or mod 2

I wouldn’t worry about stresses in your lower, I’ve run 7.62 x39 in an m16 lower never had an issue

I’ve got a 7.5” Radical Arms upper that I put a cheapo muzzle break on. It’s a great big fireball. Very loud too.

Appreciate the feedback,  now to find a 7.62x39 upper or build one out.

I'm not sure I want the beltfed upper,  seems like that 150 round saw drum does the same thing and is simpler.

Ok I ordered the parts to build a 10.5" upper.  Everything is good parts but I am not finding many in-stock barrels and ordered some POS barrel from Midway.  If anyone has a 7.62x39 barrel connection let me know, thanks!

YHM used to make some nice 7.62x39 stuff. Not sure what they’re doing now. I’d look there. For auto, I prefer cheap stuff since it’s getting beat on so much. I’ve been using a $40 barrel for 5.56 for about eight years now. Still works fine.

what type of ammo have you shot through it did you use an extra power hammer spring for the hard primer stuff  
thanks PeterNNH

I shoot mostly wolf and Tula through my 7.62x39 upper. I just have a standard hammer spring. I’ve not had any issues.

I had one destroy a buffer this weekend. I'm not exactly sure why either...

PSA has 10.5's in stocks as well as their BCG's.  The carriers are clearanced for AK mags but there is no harm in using them in a standard upper.
https://palmettostatearmory.com/ks-47/parts.html

Now there latest Gen uppers have stops in them so if you use an AK mag as a monopod it won't  rub on the bottom  of you carrier so don't get that unless you don't mind cutting them off as it will interfere with an AR pattern 7.62x39 mag.
More info on my site: https://c3junkie.com/?page_id=185

Ten or twelve years ago I had Wolf steel case 7.62x39 ammo destroy a buffer when I was shooting full auto.  It was the only time I've ever had M16 trigger slap.  It was then that I stopped shooting steel case ammo of any type.  Never had an issue using brass case ammo before and after that.  I eventually traded away the upper (and about 300 rounds of brass case ammo) with the warning to only use brass ammo.

MHO, YMMV etc.  Be well.

Never had an issue.  

Not related to your question.  I also use the first generation OSS 7.62 can.  The one with the muzzle device that the ATF deemed was a suppressor part.  So I had to dedicate the suppressor to a rifle, and with the flow through design I wanted to put it on an auto upper.

The combination of 7.62x39, flow through oss suppressor and auto is really fun.

I wish I could post a picture of the buffer but the Submit button is gone on my brave mobile browser. Anyways, it destroyed the plastic retaining piece on the end.

The buffer that was crushed:


ETA: FWIW, I also have a semi auto AK47 that shoots the Wolf steel case 7.62x39 without any problems.

Now THAT was a seriously over-gassed barrel!!

+1.  I think many 7.62x39 AR barrels are over-gassed.  Then when the are gassed right, I still like to slow down the cyclic rate some to get them in the 600's.  
My preferred configuration below:
I don't run the shorties suppressed, they are just blasters.  I run them 100% with any steel cased ammo and they all run 100%.  I have several 7.5 and 8" uppers.  I have one barrel that is a smooth bore from all the rounds that I retired.
Since I don't run them suppressed, I just get an undersized lo pro gas block and drill it out.  Back when I had my business, (MicroMOA) I had a block called the Baby Govnah which is just a lo-pro with a countersunk hole and a .043" gas port hole for $20 that you could open up yourself or I used to do that for an additional $10.
Today, YHM has the same thing but their port is .054".  I think they sell them for around $20 retail as well.  I see them even cheaper at Midway.
I checked my notes and I tested a 8" 7.62x39 barrel that came with a .099" gas port.
Using a standard power spring, H2 buffer and standard non weighted carrier yielded a cyclic rate of 1060RPM.
I dropped the port down using one of my Govnah's down to .0625" and the same configuration ran at 764 RPM


I don't think you can get the SAW weight anymore but KAK sells a short tungsten weight.

As I had on a number of occasions over several years previously shot many rounds of the same Wolf steel cased ammo as well at least a couple of brands of American made brass cased ammo without any issues or excessive rate of fire before and after the incident, I am reasonably certain it was a "hot" load round, and not an over-gassed system.  And further, the guy I traded the rifle to has shot at least 200+ rounds of brass cased, American made 7.62x39 ammo without incident since he has had the gun.  Brass cased 7.62x39 ammo tends to be more pricy than 5.56x45 ammo so he doesn't shoot the 7.62x39 rifle very often.
ETA:  FWIW, the crushed buffer that I used with the 7.62x39 upper was configured as an "H3", i.e., three tungsten weights.  I did not have a rate of fire timer at that time, so I don't have the numbers.

MHO, YMMV, etc.  Be well.

Here is mine after it was destroyed.
Attached File

If the buffer is hitting the end of the receiver extension that hard, my concern would be the threads of the receiver extension pulling out of the registered receiver.

Scott.

My experience is that most 7.62x39 AR15 uppers are going to have noticeably more recoil than their 5.56x45 counterparts.  Now I have never destroyed a buffer like some of the posts above, but I can also feel the recoil impulse is greater on every 7.62x39 upper I have ever shot including my personal 7.62x39 upper.

As mentioned above many of the 7.62x39 uppers are over gassed out of the box which doesn't do you any favors in the recoil department as it throws the carrier back much harder than needed to cycle the action.  I presume that commercial manufacturers generally over-gas their 7.62x39 barrels/uppers  so they will run on a much wider selection of shitty former com-bloc /surplus ammo.   7.62x39 also has a  lower chamber pressure of ~45K vs. ~60K psi so there is less pressure to work with which is why I assume 7.62x39 uppers gas ports are larger in the 0.090" to 0.11" range vs. 5.56 which are usually around 0.06" to 0.08" range for a mid length barrel.

Even if you remove the carrier impact to the receiver extension recoil perspective, 7.62x39 has ~20% more energy at the muzzle than 5.56x45. (~1300ft/lbs vs. ~1600ft/lbs;  this obviously can obviously change vis the specific load and barrel length)  So even if your AR didnt have a semi-auto gas system there is still going to be more recoil energy transmitted into the receiver via the front and rear takedown lugs due 7.62x39 having a higher ft/lbs of energy which is always going to translate into more reward recoil.

Personally I don't shoot my 7.62x39 upper on my transferable M16 lowers much out of concern for additional wear/team.  I even have a MicroMOA gas block with a custom drilled plate on AR 7.62x39 upper to tune it so the carrier recoil speed/ROF isn't to high.   I use (or used) to use primarily use my 7.62x39 upper with one of RLL instead so wear and tear went on a cheap title-1 lower.  However ever since I set up a CMMG Mutant to run with one of my RLLs I really don't shoot the standard AR/M16 7.62x39 upper much as the Mutant is softer shooting, I don't have to be concerned about bolt lug(s) breaking due to the AR10 sized bolt head, and it takes standard 30rd AK mags.

+1.  All your other points were spot on.
I too run my 762x39 uppers only with my RDIAS and MGI modular lower.  It was initially to use the AK magwell for unmodified AK mags/drums.  I had a broken hammer pin running 7.62x39 with this setup.  Thank God I had the muzzle pointed safely downrange.  When I chambered a round, the hammer would let go due the broken hammer pin and lit a round off.  Now since the MGI lowers magwell covers the top of both sides of the hammer pin, I switched to using KNS trigger pins which have no middle groove and have never broken one again.
This is back when I was also running a blowback 9mm as well.  Which we all know are hard on hammer pins.  So I don't know if running 9mm helped wear it out but it was definitely 7.62x39 that broke it when I had the AD.