New build doesn't run!

[Mike_M]

New AR build (my first). Rounds aren't ejecting. I have no pictures of the issue, but let me see if I can describe it. Chambered round fires, but then the case gets stuck between the barrel extension and the bolt. ALMOST straight ahead. Sometimes it works and ejects the round, but ejection is weak. Of the rounds that eject (maybe 30%), only half of those will strip a new round off the magazine. Also, the bolt is probably only locking back on an empty magazine sometimes. This was 2 different range sessions. After the first range session, I did some research and thought I just didn't have enough lube on the bolt. So I lubed it up with Tetra Gun Lube and went back to the range. No improvement. I basically have a single-shot AR.

I'll try to remember everything I used in this list, but if anybody sees something that is an obvious mis-match of parts, let me know...

18" Black Hole Weaponry barrel - mid length gas (5.56 1:8 twist)

YHM low profile gas block

YHM Todd Jarrett 15" handguard

Rainier Arms NiB BCG

Aero Precision upper

BCM charging handle

Spikes Lower

CMMG LPK

Vltor E-mod A5 stock kit

The thing I was going to do next is to take the hand-guard off and see if I can figure out if my gas block is somehow not positioned correctly. I know I'm getting air through the gas tube but maybe it's off just enough to restrict the amount of gas I'm getting to the bolt. It just seems like it's under-gassed which should NOT be my problem with an 18" mid length barrel, right?! Could the A5 stock be "too much"? I read that it's good for taming over-gassed guns, so maybe it has too stiff of a spring or the wrong kind of a buffer for my application?

Any ideas?

Oh, I did try 2 different boxes of ammo. I shot a box of Independence 5.56 55gn (?) FMJ and also shot some Federal XM193 in 5.56 as well. After about 3-4 rounds of the Federal ammo with no improvement, I figured I was just wasting ammo at that point so I called it a day.

Ah, one last thing to note - I did inspect all the fired cases and saw no signs of any bulging or primers being pushed out, etc. Cases looked fine other than a light "scratch" (probably from a feed ramp or something?)

Thanks,

-Mike

Edited December 26, 2013 by Mike_M

[Sarge]

I know zip about building an AR but it sure sounds like it's not getting enough gas to this lay person.

[ToysRUs]

Pull the gas block and mic the distance of the gas port to the front of the block.

measure the barrel port and mark where the front of the block goes.

reassemble lining everything up.

Try again!

Edit: because I can't spell....

Edited December 26, 2013 by ToysRUs

[02Fatboy]

Is the gas block adjustable? If so you will need to adjust for the load you are using.

[Doug H.]

Here is a copy of a post I made in another thread about gas systems:

Could still be a misaligned gas block. I usually use a .025 feeler gauge to set the gas block slightly forward then test the gas by taking off the comp, droping the bolt and running compressed air into the muzzle. You can hear the change in gas as you move the block around. When you get the best air flow you have reached the sweet spot and that is the maximum air flow through that block. If that doen't work try a different gas block. I would try all those thing before I enlarged the hole in the barrel.

Doug

[polymerfeelsweirdman]

I would look at the gas system parts and maybe even the extractor

some things you could look at:

-if the gas block is directly over the gas port

-if the gas key is staked and seated right

-if the gas tube is messed up or not

[co-exprs]

Pull the gas block and mic the distance of the gas port to the front of the block.

measure the barrel port and mark wehre the front of the block goe.

reassemble lining everything up.

Try again!

This is more than likely the culprit. The difference in the two spec's is about half a hole dia. I ran into this problem on my first build, but happened upon a thread entry from Kurt Miller describing the mismatch. Fortunately for you, the offset will be in your favor and you will simply need to (if this is indeed the problem) slide the gas block away from the shoulder .025".

[Mike_M]

I'll pull the handguard off tonight and spend more time aligning that gas block. Admittedly, I kind of eyeballed that step based on some Youtube videos I saw. It seemed werid that they weren't measuring or marking a thing, but just lining things up by eye. Should have followed my gut on that one. I'll give it another try tonight and try the compressed air trick to see if it confirms my "measurements".

If I pull that block off, I'm hoping I'll see some kind of carbon build-up on the barrel that will show a partially blocked port.

Nope, not an adjustable gas block. Speaking of which - why run an adjustable gas block? Seems pretty easy to "turn down the gas" on a non-adjustable one! ;-)

Thanks guys.

-Mike

[co-exprs]

Adjustable gas is for fine tuning the action. You already have the YHM and it will work just fine. Run it until muzzle manners become an opportunity to gain a spot or two on the leader board. If your gas block is the one with set screws on the bottom... one of the set screw holes lines up with the gas transfer hole in the gas block. Many barrels come with a small set screw indentation on the bottom of the barrel. This is usually placed exactly opposite from the gas hole. A quick look will tell you if you can use the gas block set screw hole and the matching indentation on the barrel as a guide. If that is the case, you simply pull out the set screw opposite the gas transfer hole in the gas block, align the set screw hole with the indentation on the bottom of the barrel and install the set screw, locking the gas block into place. If it all works out as I've described, then you should either have no gap at the shoulder or a .025" gap (give or take). If you don't have the set screw gas block or an indentation on the bottom of the barrel, then you will need to remove the gas block and use calipers to measure the two hole locations. If you double check and everything is lined up as it should be... then I'm all wet and you'll have to find another root cause.

[Mike_M]

Ok, I pulled the handguard off and took another look at the gas block and gas tube. I don't really think it's that simple unfortunately. The hole in the gas block is pretty generous and I think it would be pretty hard to cover up the port in the barrel. My calipers says I can run the gas block up against the barrel flange and still be OK. Even if I was way off I think I'd still be getting 90% of my gas into the gas block. I should be getting plenty of gas.

I chambered an empty case (was NOT deformed at all) to help block the air flow around the bolt so I could try the air compressor trick to see if I could tell any difference as I moved the gas block around. Again, not much difference in air flow unless I pull it away from the shoulder on the barrel. But when I went to remove that case I had to pull on the charging handle with quite a bit more force than I was expecting. So not sure what the deal is with that?! Any thoughts?

Are Raineir BCGs OK quality? Could this be a headspace issue (no I didn't check)? Should I try some .223?

-Mike

[1911 S.I.S.sy]

OK. Have you checked the buffer and spring to make sure that it is moving freely and the roll pin hasn't moved to catch the spring and essentially causing it to short stroke. And make sure the buffer and spring are lubed.

[Sarge]

Was the empty case you inserted sized or just straight out if the brass bucket?

[polymerfeelsweirdman]

you know, your problem might be from your buffer assembly

when you installed the stock did you make sure to cover the edge of the buffer retainer? it could explain what you're seeing. it is easy to forget and makes a big difference in whether or not the rifle is a single shot buffer retainer spring mangler or a normal functioning rifle. luckily this is an easy fix but it might require a new buffer retainer spring and/or buffer retainer

another possibility is the chamber being out of spec. not sure if that could cause these symptoms because I haven't actually seen it, but it seems plausible

[BritinUSA]

I once saw a guy shoot a brand-new AR-15 and he was having the exact same problem. Turned out he did not have enough lubrication on the bolt, the application of some slide-glide that I had with me had it running perfectly.

[wgj3]

Gas tube alignment with carrier key could also be the culprit if the barrel nut shifted at all and moved the gas tube.

Also, always try a different magazine or two so that you can eliminate that as the problem.

[wgj3]

Dang double-tap...

Edited December 27, 2013 by wgj3

[ben b.]

OP: You have not commented on how the gas tube/gas key interface is working. Does the gas key slide over the gas tube with no interference/friction? Does the BCG slide easily when manipulated by hand?

I like to install the tube & gas block with the BCG without the bolt in the receiver, so that the gas tube at least starts inside the gas key. This lets you see if some adjustment is necessary. Finer adjustment of the tube's position comes later.

[Mike_M]

OK. Have you checked the buffer and spring to make sure that it is moving freely and the roll pin hasn't moved to catch the spring and essentially causing it to short stroke. And make sure the buffer and spring are lubed.

I'm not sure I understand which roll pin would move to catch the spring, but I can cycle it fine with the charging handle. The buffer tube catches the edge of the buffer retainer perfectly. No lube on the spring, but it's brand new clean.

Was the empty case you inserted sized or just straight out if the brass bucket?

Straight out of the brass bucket. I tried about 3 or 4 different ones. All seemed "tight", but you're right, they weren't sized or anything...

you know, your problem might be from your buffer assembly

when you installed the stock did you make sure to cover the edge of the buffer retainer? it could explain what you're seeing. it is easy to forget and makes a big difference in whether or not the rifle is a single shot buffer retainer spring mangler or a normal functioning rifle. luckily this is an easy fix but it might require a new buffer retainer spring and/or buffer retainer

another possibility is the chamber being out of spec. not sure if that could cause these symptoms because I haven't actually seen it, but it seems plausible

I guess if the chamber is out of spec, that's the thing that probably takes this thing above my skill level to diagnose and correct. Bummer. I hate to just turn it over to a gunsmith. I don't learn anything if I do that...

I once saw a guy shoot a brand-new AR-15 and he was having the exact same problem. Turned out he did not have enough lubrication on the bolt, the application of some slide-glide that I had with me had it running perfectly.

I saw a guy use bearing grease on Youtube. All I have is Tetra Gun Lube, but it's a lot thinner than bearing grease. Still, the bolt appears "messy oily", but perhaps I'm not using the right product for the job?

Gas tube alignment with carrier key could also be the culprit if the barrel nut shifted at all and moved the gas tube.

Also, always try a different magazine or two so that you can eliminate that as the problem.

I have 35lbs torque on the barrel nut and only fired the rifle like 3 times before I had my first ejection issue. But I've got it apart enough now, I may as well double check that. I can pull that nut off again and re-do.

Thanks for the ideas guys. Sure appreciate the help.

-Mike

Edited December 27, 2013 by Mike_M

[Mike_M]

OP: You have not commented on how the gas tube/gas key interface is working. Does the gas key slide over the gas tube with no interference/friction? Does the BCG slide easily when manipulated by hand?

I like to install the tube & gas block with the BCG without the bolt in the receiver, so that the gas tube at least starts inside the gas key. This lets you see if some adjustment is necessary. Finer adjustment of the tube's position comes later.

ben, I'll try pulling the bolt out and see what it's like. I did note a little "wear" on one side of the gas tube that surprised me given the few number of rounds this thing has seen. I was looking at that gas key gas tube interface tonight and wondering how I troubleshoot if there's an issue there. since I can't really "see" the interface. I'm actually highly suspicious of this interface. What do you mean "finer adjustment comes later"? Do you actually "bend" the tube a bit with a flat blade screwdriver or something for better alignment?

-Mike

[ben b.]

... What do you mean "finer adjustment comes later"? Do you actually "bend" the tube a bit with a flat blade screwdriver or something for better alignment?

-Mike

Exactimundo. Can use some paracord if it needs to be pulled down.

http://www.weaponevolution.com/forum/showthread.php?1613-FAQ-s-BASIC-INSPECTIONS-AND-PROCEDURES

[Dan Sierpina]

Did you use an alignment pin in the carrier key when you were installing the barrel nut? It doesn't take much to move the gas tube and have it rub.

[chevyoneton]

If the key is not binding on the gas tube, is it tight and properly staked? Is the key clear (run a pipe cleaner through it). Does the bolt rotate freely bak and forth within the carrier? Are teh gas rings properly aligned on the bolt? And I know you said it was passing air, but are you SURE the tube is free and clear? And, this one is almost too obvious to mention, have you tired some known GOOD strong ammo?

[Mike_M]

Did you use an alignment pin in the carrier key when you were installing the barrel nut? It doesn't take much to move the gas tube and have it rub.

Nope. This is a new one to me. An alignment pin in the carrier key, huh? I'll Google that when I get home.

Would a gas tube being slightly off be enough of an issue to keep the gun from running though? I mean, if the bolt is dropping, the gas tube MUST be going into the key or else it would hang up and not go into battery, right? I also wonder if maybe the gas tube might be out of spec? If a gas tube was too "thin" and didn't form a good seal on the gas key it'll cause a bit leak there, yeah? Maybe I need to see how well the gas tube I have "fits" in the gas key?

-Mike

[Mike_M]

If the key is not binding on the gas tube, is it tight and properly staked? Is the key clear (run a pipe cleaner through it). Does the bolt rotate freely bak and forth within the carrier? Are teh gas rings properly aligned on the bolt? And I know you said it was passing air, but are you SURE the tube is free and clear? And, this one is almost too obvious to mention, have you tired some known GOOD strong ammo?

Key is tight and staked. Air compressor on the gas key positively "pops" the bolt forward. I did make sure the gas rings weren't all lined up forming a leak there. As for ammo - I used Independence 5.56. Is that stuff crap? Well, I think I also used about 5 rounds of the XM193 Federal stuff too I think (brown box). These aren't reloads. Is it possible the barrel is mismarked and it's actually a .223 barrel? What would the expected result of firing 5.56 in a .223 barrel be?

PS - I have NOT run a pipe cleaner through the gas key, but I sure can try that tonight...

Edited December 27, 2013 by Mike_M

[02Fatboy]

Mike find someone in your area and have them look at the gun. We can set here all day and guess wants wrong with it are you can get fine someone that can lay hands on and get it fixed. just my 2cents.