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Too much headspace on new AR15 build

mac1911

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Most grades of Loctite break down with heat, and the rifle is dumping hot gas through the gas key nicely heating those two screws. Staking isn't temperature dependent, and also gives a visual indication on whether those screws have backed out at all. In addition, both parts deformed by staking are replaceable and relatively cheap. The highest service temp I could find for a Loctite threadlocker is 400F, which would probably work - I've never measured gas key temps during shooting. The first indication of a threadlocker failure would be the screws backing out, and I guess I consider the gas system critical enough to stake it and not have to think about it other than checking the staking when the BCG comes out.
Also loctite dies not like to cure on coated metals like park or any othet type of coating. This is why loctite has a primer
 
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I don't remember if the bolt locked back with a single round, unfortunately.

So to summarize this thread:

- Go to a gunsmith, but also don't and try to figure it out yourself
- Headspace shouldn't be a problem so you shouldn't need to check it, but also can be problem, so definitely check it
- A carbine gas system with rifle buffer might be a problem, but also shouldn't be a problem
- Contact the manufacturer
- Buy a new bolt
- Fix the probably wonky gas system

I know in the end I have to make my own damned decisions, and appreciate all the opinions. I just find it funny how contradictory they can be. I was hoping someone could say this thing were safe to test fire, but no one can actually tell me that, and I shouldn't trust the opinions of random people on the Internet for safety.

Side note on Clymer headspace gauges: their .223 and 5.56 NOGO gauges are different! I don't think they should be, but they are. 5.56 is 1.4696, whereas .223 is 1.4666. For NATO gauges Forster seems to only offer the GO and MAX (which I take as field gauge) these days.

I've decided that I probably should:

- Finish my build finally, and register the damn thing
- Get a field gauge, and make sure it doesn't close on that
- Work on the cycling problem
- Find a gunsmith if I can't figure it out

Thanks for everyone's time!
OK.

Good luck.
 

insomniac

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Any headway on this matter?
I see what you did there.

Sooooo.....when I was headspacing, I, uh, may have forgotten to put the bolt cam pin back in. Super obvious in retrospect, because the bolt cam pushes the bolt forward a little. Great Road Firearms showed me and didn't even call me an idiot at the same time, so I'm super grateful.

I do have a cycling problem. First round fires fine, cycles. Second round fires, and then *click*. I'll find that the bolt is half open and has scraped the side of the next round. I tried it in both .223 and 5.56 for kicks, and this was on a carbine buffer. Looks like I'm gunsmith bound, because I'm missing the tooling to tear it down.
 

richc

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I'm guessing gas tube problem. Are you using the right tube? I've seen that happen.

Is the gas block installed properly? Is the gas tube protruding far enough to engage?

There should be plenty of energy available to cycle the action. Sum Ting Wong.
 

KMM696

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Not a high probability problem, but one more thing to check.

If first one fires, second one jams can be translated as cartridges loading from one side of the magazine work fine and the other side jams and your upper has M4 style feed ramps that extend from the receiver through the barrel extension, check the feed ramps to make sure the feed ramp section of barrel isn't protruding a bit, catching on the bullet tip or edge of the case mouth. It's okay if the feed ramp on the receiver is higher than the barrel ramp, as that just creates a little cliff for the cartridge to fall off of on it's way to the chamber. If the barrel ramp is higher, it's a wall for the cartridge to run into.

It's 5 minutes work with a dremel and pointed grinding wheel to fix, but you should try to find someone who's done it before.

this AR15Barrels.com link


is to a picture that is intended to show the difference between standard and M4 ramps, but it also gives a good idea where to look for misalignment.

Good luck.....
 

jayhitek

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I disagree, In a situation like this, the first one usually fires fine because the BCG is manually thrown forward when you release it with the button and it picks up a cartridge with all that force behind it.. the 2nd bullet is now relying on the gas and buffer cycle..
I think asking him to tweak the feed ramps is a drastic step to take right out of gate before swapping a few parts to see if it changes anything..
 

KMM696

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I'm asking him to check the ramps. If they need work, I told him to find someone who knows what they're doing. It's an accumulated budget build, so he probably doesn't have boxes of spares lying around to start swap-out troubleshooting. Feed ramps he can check with a pencil or a nail or a cocktail straw or.... you know, something he can do with what he's got lying around the house.
 

mac1911

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I see what you did there.

Sooooo.....when I was headspacing, I, uh, may have forgotten to put the bolt cam pin back in. Super obvious in retrospect, because the bolt cam pushes the bolt forward a little. Great Road Firearms showed me and didn't even call me an idiot at the same time, so I'm super grateful.

I do have a cycling problem. First round fires fine, cycles. Second round fires, and then *click*. I'll find that the bolt is half open and has scraped the side of the next round. I tried it in both .223 and 5.56 for kicks, and this was on a carbine buffer. Looks like I'm gunsmith bound, because I'm missing the tooling to tear it down.
Maybe a video of the problem.

so you get 2 shots off and when feeding 3rd shot it fails to feed and bolt is not closed...?
Try other magazines.

What you should do.
1. Load 1 round in the mag, seat mag cycle charge handle.
does cartridge chamber if yes go to Fire the one shot , does bolt lock back? If yes go to 2 . If no you have a mechanical issue.
2. Fire some more single shots- confirm all is well.
3.load 2 rounds and continue.

Once you can duplicate the problem you can start to figure it out. Start with a different mag.
 
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Let's all be perfectly clear.

You have a carbine buffer, with a carbine spring, in a carbine buffer tube, correct?

If so, next stop is gas.

ETA: Here is an explainer on M4 feed ramps, courtesy of Larue Tactical.

https://www.everydaymarksman.co/wp-content/uploads/2019/03/feedramp.jpg

There is really only 1 combination that might cause you problems. Pretty low probability on a 16" barrel.
 
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CrackPot

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I agree. Gas. I recently had a problem where the gas block was out of spec. It’s opening to the barrel was not correctly offset so if pushed fully against the barrel collar it partially blocked gas flow. Offsetting it very slightly from the collar fixed all my problems. I could not replace it easily since I had already pinned the muzzle break.

not all parts are in spec. Focus on the easy ones first. Gas.
 
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I assume you tried a different mag first.
Probably best not to assume anything, but (assuming he isn't using a carbine spring and buffer in a rifle-length buffer tube) the problem sounds like short stroking.

Check gas tube for obstruction.

Lube the rifle.

Try a known-good mag.

Try a different/known-good bolt to rule out leaky gas key.

Try a heavier buffer (on the off chance that the rifle is so over-gassed that the bolt velocity is too fast to allow the mag to feed). Usually over-gassed feeds just fine, but fails to lock back on an empty mag.
 

Supermoto

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I agree. Gas. I recently had a problem where the gas block was out of spec. It’s opening to the barrel was not correctly offset so if pushed fully against the barrel collar it partially blocked gas flow. Offsetting it very slightly from the collar fixed all my problems. I could not replace it easily since I had already pinned the muzzle break.

not all parts are in spec. Focus on the easy ones first. Gas.
Thats because some gas blocks are designed so that they can be used with a handguard cap. You need to leave a 1/32" gap to the barrel shoulder if you are using a free floating handguard. Easy way to tell on a set screw gas block is to spin it upside down. The gas port is drilled thru the set screw hole, so you can see the alignment and know if you need to offset or not
 

1903Collector

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I see what you did there.

Sooooo.....when I was headspacing, I, uh, may have forgotten to put the bolt cam pin back in. Super obvious in retrospect, because the bolt cam pushes the bolt forward a little. Great Road Firearms showed me and didn't even call me an idiot at the same time, so I'm super grateful.
That could have ended badly if you fired it!

I must be a lucky SOB, I got about 2 dozen builds under my belt, they all worked 100% from the get go or just need a couple mags to loosen things up a bit. Hope you get yours up and running.
 

insomniac

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Woo, activity on this thread! Unfortunately I haven't had time to get out to the range to further diagnose, but I figure at this point it's almost certainly the gas system.

Let's all be perfectly clear.

You have a carbine buffer, with a carbine spring, in a carbine buffer tube, correct?
Correct. I did have feed problems on a rifle buffer, spring, and tube as well, but replicated it with carbine buffer, spring, and tube.

I assume you tried a different mag first.
No, but on the rifle buffer, spring, and tube, I was using a different mag. I will try a different mag next time I get out to test fire, but these were brand new ten round magazines so I doubt this is the problem.

That could have ended badly if you fired it!

I must be a lucky SOB, I got about 2 dozen builds under my belt, they all worked 100% from the get go or just need a couple mags to loosen things up a bit. Hope you get yours up and running.
Oh, no, I wasn't trying to fire it with the cam out; I meant when I was headspace checking, I left the cam out.

I think the vast majority of builds have no issues, I just must have mucked up the gas tube installation or something. Unfortunately I don't have the tools to do a tear down yet.
 
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How far are you from Harvard Sportsmen's club?

It's going to be raining Saturday in the am, but it shouldn't suck too bad later in the afternoon.

I'd propose trying a known good mag, bolt, and maybe even an H/H2/H3 buffer on a known good carbine lower.

Let me know if that might work for you.
 

CrackPot

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How far are you from Harvard Sportsmen's club?

It's going to be raining Saturday in the am, but it shouldn't suck too bad later in the afternoon.

I'd propose trying a known good mag, bolt, and maybe even an H/H2/H3 buffer on a known good carbine lower.

Let me know if that might work for you.
Good advice. I keep a box with 3 different weight buffers, 2 different springs, known good mag and some tools. I also have a "known good carbine" so full upper and full lower both that are in spec and function and have been cross tested with other uppers/lower. I also have a known good rifle. Then when I have a problem child, I take the good rifle or carbine and the box of stuff to the range and isolate. swap in upper and lower to figure out where problem is (upper or lower). Then start changing parts out to figure out the issue. My last issue was the 1/32" offset on the gas block. The time before that it was a gas issue addressed with buffer weight. etc.
 

mac1911

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"Generally" if you have a gas system problem with fail to feed issues its constant.
I would not mess with the buffer system unless the wrong parts are installed in the wrong tube.
Your not going to have cycling issues with any "normal" length buffer tube and spring/buffer set up.
A rifle length gas system will and should function fine with a carbine buffer set up and a carbine gas system on a rifle length buffer set up.
As for gas system problems , I only been messing with ARs since 2008. What I have seen amongst friends.
Loose or material stuck in gas key. Loose gas tube= did not pin the tube in gas block. i have come across 2 bad gas ports.
One in which the hole was not drilled through. The other was drilled off line and the gas block covered about 1\2 the hole.
Good thing was it was a optics only rifle so we just off set the gas block and drilled a few divots for the set screws in the correct location.
The highest problem has been mags or grossly out of spec discount parts.
 
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"Generally" if you have a gas system problem with fail to feed issues its constant.
I would not mess with the buffer system unless the wrong parts are installed in the wrong tube.
Your not going to have cycling issues with any "normal" length buffer tube and spring/buffer set up.
A rifle length gas system will and should function fine with a carbine buffer set up and a carbine gas system on a rifle length buffer set up.
As for gas system problems , I only been messing with ARs since 2008. What I have seen amongst friends.
Loose or material stuck in gas key. Loose gas tube= did not pin the tube in gas block. i have come across 2 bad gas ports.
One in which the hole was not drilled through. The other was drilled off line and the gas block covered about 1\2 the hole.
Good thing was it was a optics only rifle so we just off set the gas block and drilled a few divots for the set screws in the correct location.
The highest problem has been mags or grossly out of spec discount parts.
Thanks for the sage advice.

Why don't you meet up with him?

And just out of curiosity, how are you going to rule out over-gassed/bolt velocity issues?
 

insomniac

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Thanks for the offer, can't do this weekend (out of town). The upper assembly (sans the upper itself, which is just a milspec M4 flat top upper) is from Wyndham Weaponry, so I'd hope it's alright. Maybe I can use this as an excuse to finally buy a bench vise.
 
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Thanks for the offer, can't do this weekend (out of town). The upper assembly (sans the upper itself, which is just a milspec M4 flat top upper) is from Wyndham Weaponry, so I'd hope it's alright. Maybe I can use this as an excuse to finally buy a bench vise.
OK.

Here is a thread from someone with the exact same symptoms.

I found it googling "Boise Tactical".

AR 15 not picking up the next round

His issue turned out to be a mis-aligned gas tube.

Good luck.

ETA: My final word of advice in this thread would be this: Don't buy cheap parts. Ever. Buy good parts from known manufacturers on sale. Always.
 
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insomniac

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Interesting thread! Good find. The BCG on paper sounds really good. In that thread it appears he had a misaligned gas tube, so that gives me an additional thing to consider. Maybe I'll see if I can borrow a friend's BCG to test later.
 

mac1911

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Thanks for the sage advice.

Why don't you meet up with him?

And just out of curiosity, how are you going to rule out over-gassed/bolt velocity issues?
I have offered to meet up, times and distances dont agree
I personally can not say I have successfully diag or even see Over gassed system that I can say "yup over gassed" . Generally from what I have gathered over the years over gassed system will tend not to pick up or even lock back on last round and have a tendency to damage parts.?
 
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