Some ar 10 help requested

44man · Oct 5, 2018

Ok, my sons best friend purchase an ar 10 lower and built it himself, I have no idea what brand but I will try and find out.

He purchased an ar 10 upper, again idk what brand it’s just marked .308 on the barrel.

He fired it at the far about 20 times and it ran fine.

He showed it to my son because it looked really dirty, so they called me. I recommended cleaning it and lubing it because they said it was really dry.

They also said the bcg was hitting the back of the lower.

So they cleaned the outside of the bcg with my break cleaner and dunked it in Mobil 1 and let it drip dry, they added $2 worth of quarters behind the buffer spring and the bcg no longer bottled out and put it back together.

Immediately it started stovepiping. I told them to try it with the quarters removed, again stove piping and bottoming out hard so they put the quarters back in. The ran and got a lighter spring and buffer and have tried every combo they could

And it’s still stovepiping every round.

What should they try next?
What do you smarter at guys think is the problem?

And yes they say it’s all my fault.

E.Shell · Oct 5, 2018

Will it manually eject a cartridge or case?

Ejector sticking?

Extractor chipped or binding?

44man · Oct 5, 2018

They said it will eject a round manually

I need to get them to bring the bcg to me for a close up look

Could it be a gas problem?

danb · Oct 5, 2018

First thing I'd try is a new mag. Could be a mag problem. Make sure its seated with a firm tap. If it ran and then it didn't run, I'd be suspicious that they did not put it back together right when they put the quarters in. I'd check the castle nut, detent pin, etc. Check that nothing came loose on the BCG .

Next thing I'd check is the gas block. Been known to come loose on home builds. Or not be 100% aligned correctly.

Clearly, though, they bought the wrong buffer and spring. Maybe I am misreading your post - they need a heavier spring and buffer, not lighter?

44man · Oct 5, 2018

danb said:
First thing I'd try is a new mag. Could be a mag problem. Make sure its seated with a firm tap. If it ran and then it didn't run, I'd be suspicious that they did not put it back together right when they put the quarters in. I'd check the castle nut, detent pin, etc. Check that nothing came loose on the BCG .

Next thing I'd check is the gas block. Been known to come loose on home builds. Or not be 100% aligned correctly.

Clearly, though, they bought the wrong buffer and spring. Maybe I am misreading your post - they need a heavier spring and buffer, not lighter?

The lighter spring and buffer was there idea

Phoning in repairs is tough for me because I can’t see what’s going on but running and then not running seemed to be odd since all I recommend was cleaning and quarters, so yes something may well be put back wrong.

And since all they have is one mag it darn well could be a bad mag or a bent lip or the way it is seating.

Thanks

danb · Oct 5, 2018

44man said:
The lighter spring and buffer was there idea

Phoning in repairs is tough for me because I can’t see what’s going on but running and then not running seemed to be odd since all I recommend was cleaning and quarters, so yes something may well be put back wrong.

And since all they have is one mag it darn well could be a bad mag or a bent lip or the way it is seating.

Thanks

or just a dirty mag.

This is an important lesson btw, and why I never clean my AR. I am working on a project to see if I can go 2000 rounds without cleaning. so far so good! :lol2:

44man · Oct 5, 2018

danb said:
or just a dirty mag.

This is an important lesson btw, and why I never clean my AR. I am working on a project to see if I can go 2000 rounds without cleaning. so far so good!

I don’t mind dirty but I hate running my guns dry, hence having them lube the gun.

But since now it’s my “ fault “ the gun won’t run I almost wish I had stayed out of it, lol.

E.Shell · Oct 5, 2018

danb said:
....This is an important lesson btw, and why I never clean my AR. I am working on a project to see if I can go 2000 rounds without cleaning. so far so good!

We went to BulletFest and I put more than 1,000 through one rifle w/o cleaning. Just slopped the bolt carrier with oil and kept going. Wolf ammo too, stunk like cat sh!t.

What kind of ammo are they running, 44 Man?

If they are running .308s (and not 7.62) the increase in pressure could have been causing the bolt carrier to batter the lower. I have also seen numerous times that the ejector will shave off a little extruded brass and at some point, a shaving will foul the ejector, causing it to be sluggish or jam the ejector entirely.

44man · Oct 5, 2018

E.Shell said:
We went to BulletFest and I put more than 1,000 through one rifle w/o cleaning. Just slopped the bolt carrier with oil and kept going. Wolf ammo too, stunk like cat sh!t.

What kind of ammo are they running, 44 Man?

If they are running .308s (and not 7.62) the increase in pressure could have been causing the bolt carrier to batter the lower. I have also seen numerous times that the ejector will shave off a little extruded brass and at some point, a shaving will foul the ejector, causing it to be sluggish or jam the ejector entirely.

I know they are using.308 ammo so I will tell them to get 7.62 and I want to get a close look at the bcg

Qbeam · Oct 5, 2018

Was the BCG scraping the threads of the lower receiver? I am going to assume he has a DPMS pattern receiver and the correct height. Due to AR10s not being as standardized as AR15s, there may be slight differences in fitting. I see many AR10 receiver manufacturers specify the use of their upper and lower sets, and to not intermix upper and lowers. If he could tell you the receiver make, it may help.

Q

Boats · Oct 5, 2018

First off, if the barrel is marked .308 then it is chambered for .308. however, considering the rounds they were using were stout enough to batter the bcg, I would look at a fouled/broken ejector spring or a weak extractor spring. Sounds like a heavy buffer/spring and adjustable gas block would help too.

Check the bcg face for peening and check to make sure the extractor doesn't have brass or carbon built up under it.

If they are running way overgassed the bcg velocity may be enough to prematurely unseat the rear of the brass from the extractor causing weak ejection.

alucard0822 · Oct 5, 2018

AR10 gas systems, along with the bolt/spring/buffer system are harder to dial in than their little brother, and 308/7.62 has a huge variance in port pressure. Recently seen one so overgassed on commercial 308 that it was nearly ripping the rim off the brass, before failing to extract or stove piping. Add in the DPMS vs Armalite vs "not in spec for either" issues with parts compatibility, and it takes a bit more work to sort out problems, it isn't like putting together a '15

clandestine · Oct 5, 2018

They need other mags and ammo to test. Lancer is my suggestion.

If the gun has an aluminum gas block, that can be a problem too.

They need to check the carrier key bolts too. Lots of companies putting shit YFS fasteners in them and they break easily.

If the bolt is allowed to go too far past the ejection port it will stovepipe on so e uppers. I often have to open the ejection port on the front and rear to make some .308 pattern AR's reliable.

BTW, everything Ed mentioned is spot on.

I would tell them to put in a Tubb .308 Flatwire spring. That will eliminate the possible of the buffer spring going to solid height.

gtodave · Oct 5, 2018

I'm betting this is buffer/buffer spring related. I had similar issues with mine until I sorted this out. Also, it doesn't make sense that it would "bottom out" with just the spring, and adding quarters (shortening the available space for the BCG to travel) stopped it from bottoming out. It should have the opposite effect.

There are specific buffers and buffer springs for "rifles" (fixed stock) and "carbines" (collapsible stock). They need to make sure they have the correct ones in place for their application.

danb · Oct 5, 2018

gtodave said:
I'm betting this is buffer/buffer spring related. I had similar issues with mine until I sorted this out. Also, it doesn't make sense that it would "bottom out" with just the spring, and adding quarters (shortening the available space for the BCG to travel) stopped it from bottoming out. It should have the opposite effect.

There are specific buffers and buffer springs for "rifles" (fixed stock) and "carbines" (collapsible stock). They need to make sure they have the correct ones in place for their application.

good point about the quarters. had not thought of that.

I strongly suspect they got the wrong buffer/spring too.

Its also plausible to me that lubing it up decreased friction and exacerbated the problem.

clandestine · Oct 5, 2018

Both things can be happening. Too much rearward carrier travel and the buffer spring can be going to solid height.

44man · Oct 5, 2018

The wealth of knowledge on here is amazing

Thank you guys very much!!!

I love this place!

inkd · Oct 5, 2018

44man said:
The wealth of knowledge on here is amazing

Thank you guys very much!!!

I love this place!

I believe I have an extra Tubbs flatwire spring laying around if they want to try it out.

Just let me know.

Kanedog1985 · Oct 5, 2018

Yes the threaded part was getting dug up pretty bad . It's my best friends guns and he doesn't really know a whole lot about it besides it's a palmetto armory lower and he bought the upper complete online buy some guy that builds them. We have tried heavier springs, lighter springs, new mags. We are thinking it might need an adjustable gas block. Any help would be greatly appreciated.

Qbeam · Oct 5, 2018

Kanedog1985 said:
Yes the threaded part was getting dug up pretty bad . It's my best friends guns and he doesn't really know a whole lot about it besides it's a palmetto armory lower and he bought the upper complete online buy some guy that builds them. We have tried heavier springs, lighter springs, new mags. We are thinking it might need an adjustable gas block. Any help would be greatly appreciated.

Was it built with the PSA (Palmetto State Armory) upper, or a DPMS (taking a guess) pattern upper? The rifle was not stove piping prior to the cleaning? I am concerned that just by lubricating the system it started stove piping. It is odd that lubricating, which allows smoother movement of metal on metal would cause stove piping when metal on metal would likely be more binding causing stove piping.

I'll defer to Clan and Ed to figure this one out; it is past my skill set at this time.

You're in good hands, and they'll get you sorted out.

Q

Some ar 10 help requested

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