Headspace issue

Mike52793

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Hello. I have an ar build going with a rosco 5.56 16inch heavy barrel and a lantac bcg. All components to this rifle are new. The rifle passes the field and no go test, the bcg will not close. But on the go gauge it will also not close without being pushed and its hard to pull the charging handle back. Could this be because everything is brand new or the bolt/barrel is out of spec. Also am using rimless foster gauges.
 

Mountain

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Possible you actually have a .223 chamber? They tend to be tighter than the typical mil spec 5.56 chamber.
 

snax

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I had a barrel where the pin was off by just a bit. BCG wouldn't close.
I sent the barrel back to Anderson and they replaced it.....
But you'd run into issues with that even before you headspace it anyway.
Therefore this post adds nothing of value to this thread
 

kope

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If its closes on the go gage, build it and run the piss out of it.

Check out SOTAR on youtube , he's got a slew of great videos with even better audio.

Where are you located? Can you try another bolt from an NES member ?
 

mac1911

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Can be a pita but pull the barrel off and the bolt from the BCG and check your head space that way.
My guess is theres crud somewhere.
 

Uzi2

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Did you thoroughly clean the chamber before any checking?

Get a sharpie marker and color the shoulder area completely and back down the body of the GO gauge about halfway. Insert it carefully and close the bolt. Then extract it carefully and see if there is an obstruction mark on the forward surface of the gauge. The ink will be rubbed off.
 
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Mike52793

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The rosco barrel and the lantac enhanced bcg are brand new. This gun has never been fired. I just put my friends brand new bcm and it closed like a dream. Curious if it is a defective lantac
 

Uzi2

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The rosco barrel and the lantac enhanced bcg are brand new. This gun has never been fired. I just put my friends brand new bcm and it closed like a dream. Curious if it is a defective lantac

Just because some part is new ( particularly a barrel ) that doesn't mean it's clean. There could be any type of debris in the chamber from handling, shipping, etc.
Measurements should always be made on a "cleaned" chamber.....as in brushed and patched dry.

Are there any wear marks on the rear of your bolt lugs from engaging the barrel extension?
 
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mac1911

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Just because some part is new ( particularly a barrel ) that doesn't mean it's clean. There could be any type of debris in the chamber from handling, shipping, etc.
Measurements should always be made on a "cleaned" chamber.....as in brushed and patched dry.

Are there any wear marks on the rear of your bolt lugs from engaging the barrel extension?
a new gun is never a clean gun.....if I had digital camera 20 plus years ago I could show you some nasty stuff that came out of a few new guns.
Also these days they put a good amount of rust preventive goo on guns. some is a fine thin film others can be like crusty wax. Clean the shit out of everything and try again.
 

Mike52793

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You can see a little wear on the rear lugs. The 1.4646 nato gauge needs alot of pressure to close and the 1.4636 .223 gauge still needs pressure. Both hard to pull charging handle. The new bcm passes all gauge tests. Also measured the lugs front to rear and its reading 0.278 which i believe is in spec. Ive read that some people have trouble with the NiB/TiN coating versus phosphate or nitride.
 
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Uzi2

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You can see a little wear on the rear lugs. The 1.4646 nato gauge needs alot of pressure to close and the 1.4636 .223 gauge still needs pressure. Both hard to pull charging handle. The new bcm passes all gauge tests. Also measured the lugs front to rear and its reading 0.278 which i believe is in spec. Ive read that some people have trouble with the NiB/TiN coating versus phosphate or nitride.

Did you clean the chamber?
 

mac1911

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You can see a little wear on the rear lugs. The 1.4646 nato gauge needs alot of pressure to close and the 1.4636 .223 gauge still needs pressure. Both hard to pull charging handle. The new bcm passes all gauge tests. Also measured the lugs front to rear and its reading 0.278 which i believe is in spec. Ive read that some people have trouble with the NiB/TiN coating versus phosphate or nitride.
How can there be wear on a new part?
Pull a bullet on a unfired found and see if you can chamber a empty case
 

kope

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Shouldn't the bolt require some pressure to close on a round/gage and aren't the 223/556 go gages the same at 1.4636 ?

I'm sure there is someone local to you with an unfired bolt to try as an option.
 

Uzi2

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How can there be wear on a new part?
Pull a bullet on a unfired found and see if you can chamber a empty case

He stated that the Go gauge was hard closing....that would leave a mark/marks on the rear surface of the bolt lugs as they locked up. It's an indicator from his manipulation not original finish on new part.
 

Mike52793

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So I cleaned the bolt and the chamber. Also removed extractor and ejector. It will close on both 1.4646 and 1.4636 go gauge with finger pressure. But still hard to rip out with charging handle. Im curious if this just needs to break in at the range.
 

Uzi2

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It may need break in.

Upper removed from lower, Without the bolt installed in the carrier, Does your bolt carrier slide easily in the upper and not bind on the gas tube?

Have you inspected the charging handle to make sure it's not bent?

Have you inked the gauges with a sharpie to where the binding is ?
 

Palladin

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I have the exact same issue. Anderson lower Anderson upper, rifle functions fine. Except if you want to extract a live round with the charging handle, it's almost like the charging handle is locked in place, you have to tap it to get it Loose then it'll extract around
 

Mike52793

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this whole rifle is a new build with all new parts minus the preban lower shell. So after without the extractor and ejector, it passes the go gauge like i said just hard pulling handle. Took it to the range and fired 200 rounds flawlessly, not a single hiccup extracting with and without charging handle.
 

Uzi2

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I have the exact same issue. Anderson lower Anderson upper, rifle functions fine. Except if you want to extract a live round with the charging handle, it's almost like the charging handle is locked in place, you have to tap it to get it Loose then it'll extract around

Have you checked to see if the gas key is binding on the end of the gas tube?
Gas key could be cocked to one side, up or down.

School of The American Rifle ( youtube ) covered this in one of his videos. The end of the gas tube looked ok from what could be seen......the binding/wear was on the backside that is towards the upper portion charging handle channel.

Thats why you test a " new to the gun" carrier ( without bolt installed ) to see that it slides freely in the upper receiver.
 

Uzi2

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this whole rifle is a new build with all new parts minus the preban lower shell. So after without the extractor and ejector, it passes the go gauge like i said just hard pulling handle. Took it to the range and fired 200 rounds flawlessly, not a single hiccup extracting with and without charging handle.

Glad it functioned well.

When you say " hard pulling the handle" that is a very subjective term.....really doesn't convey any useable info for diagnosing a problem.
There are several things that add resistance to pulling the charging handle back, buffer spring, cam pin, gas rings, locking lugs, bolt support shoulder, bolt tail, hammer spring, bolt carrier rails, chamber surface roughness, ....all of these things are additive. Any one of them can create additional effort needed to charge the rifle.

As you found out, the rifle functions fine. New parts that are not grossly out of spec will take some firing to wear into eachother. A few hundred rounds is the usual count where things begin to smooth out.

Keep it well lubed until its broken in.
 

Palladin

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Have you checked to see if the gas key is binding on the end of the gas tube?
Gas key could be cocked to one side, up or down.

School of The American Rifle ( youtube ) covered this in one of his videos. The end of the gas tube looked ok from what could be seen......the binding/wear was on the backside that is towards the upper portion charging handle channel.

Thats why you test a " new to the gun" carrier ( without bolt installed ) to see that it slides freely in the upper receiver.
It's the same problem when I switch charging handles, switch bolt carrier groups, Etc. It's something in how the lug is locking to the barrel. Pulled back fine without a round in the chamber. With a round in the chamber you have to actually tap the charging handle with a mallet to break it free. I ran 200 rounds through it yesterday and it functions fine
 

Uzi2

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It's the same problem when I switch charging handles, switch bolt carrier groups, Etc. It's something in how the lug is locking to the barrel. Pulled back fine without a round in the chamber. With a round in the chamber you have to actually tap the charging handle with a mallet to break it free. I ran 200 rounds through it yesterday and it functions fine

If that is the case, then have you checked to see what chamber you actually have with a chamber function gauge?

Have you taken a sharpie and colored a round from the ogive all the way back to halfway on the casing to see where the interference is?

Is your front sight canted? ( indicating a possible bent or broken index pin on the barrel extension)
It only takes being one or two degrees off to misalign the extension locking lugs enough to cause a bind.

Speaking of locking lugs, what do yours look like on the rear portion of the bolt?

When you switched bcg did your upper make tool marks in the alternate bcg?

This isn't difficult to diagnose if you make some observations.
 

teamRR

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Headspace is checked without the extractor or ejector.

This is because the ejectors spring action particularly gets in the way and requires force for chambering, which is confusing. You can do a quick field check with those parts installed just isn't a great check.

Your problem isn't headspace, is likely timing or just some little machining defect. I don't know about lantac or rosco, no idea if they are top quality or bottom of the barrel, but if it was say PSA I would be blaming it on cheap parts and saying you should determine if its bolt or barrel and getting a replacement (which sounds a lot like barrel).

One knowledgeable person told me they grease the lugs and manually cycle any new barrel or bolt 200 times, ie charge it and let it slam shut, repeat. It is broken in enough to shoot when the weight of the BCG alone closes the bolt smoothly sliding down the upper at a 45 degree angle, else more dry cycling or new parts.
 
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mac1911

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It's the same problem when I switch charging handles, switch bolt carrier groups, Etc. It's something in how the lug is locking to the barrel. Pulled back fine without a round in the chamber. With a round in the chamber you have to actually tap the charging handle with a mallet to break it free. I ran 200 rounds through it yesterday and it functions fine
Keep shooting it eventually the problem will show its face in the form of wear or failure.
 
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