Headspacing issues

[number1olddog]

Alright guys here's my issue. I purchased a Sabre Defense Surplus complete barrel (16" CL) from Brownells and installed it on a Aero stripped upper (45ft lbs torque) and the Bolt carrier group is a new BCM. I am using Forster and Clymer Go and No Go headspace gauges. With the ejector and extractor out it will NOT close on the Go and as well as the No Go as it should. This is the first barrel I have installed where the bolt would not close on the Go gauge. I loaded up 5 rounds of M855 LC and checked the COL at 2.25" and with the barrel pointing in a safe direction cycled them through 5 times total on each round and re-checked the COL and it remained at 2.25". The chamber looks nice with no burrs or obstructions and is clean. Should I go ahead and shoot it or send it back. With the live rounds and some dummy rounds it functioned as it should (dry runs) with no problem.

[Iraqgunz]

Are you using .223 gages or 5.56 gages?


Alright guys here's my issue. I purchased a Sabre Defense Surplus complete barrel (16" CL) from Brownells and installed it on a Aero stripped upper (45ft lbs torque) and the Bolt carrier group is a new BCM. I am using Forster and Clymer Go and No Go headspace gauges. With the ejector and extractor out it will NOT close on the Go and as well as the No Go as it should. This is the first barrel I have installed where the bolt would not close on the Go gauge. I loaded up 5 rounds of M855 LC and checked the COL at 2.25" and with the barrel pointing in a safe direction cycled them through 5 times total on each round and re-checked the COL and it remained at 2.25". The chamber looks nice with no burrs or obstructions and is clean. Should I go ahead and shoot it or send it back. With the live rounds and some dummy rounds it functioned as it should (dry runs) with no problem.

[number1olddog]

5.56 Clymer

[number1olddog]

Just some more on this. I have a buddy who bought a DPMS AP4 barrel that I installed last week that he hasn't picked up yet so I went ahead and headspaced it with these same gauges and sure as crap it closed on the Go and not on the No Go. His BCG is a Centurion Arms. Of all the barrels to show mine up it's a damn DPMS.

ETA: When I headspaced his when I put it together all I had were Forster .223 gauges. I just got these Clymers in so this was my first test with them.

[Iraqgunz]

I only use the military Field gage, so I probably won't be able to help much on this.

[Iraqgunz]

DPMS chambers are well known for being .223 and not 5.56.


Just some more on this. I have a buddy who bought a DPMS AP4 barrel that I installed last week that he hasn't picked up yet so I went ahead and headspaced it with these same gauges and sure as crap it closed on the Go and not on the No Go. His BCG is a Centurion Arms. Of all the barrels to show mine up it's a damn DPMS.

ETA: When I headspaced his when I put it together all I had were Forster .223 gauges. I just got these Clymers in so this was my first test with them.

[number1olddog]

I only use the military Field gage, so I probably won't be able to help much on this.

So in your professional opinion (and I was hoping you were one of the ones to answer my question) if I can get a field gauge (5.56) and test it and it won't go on it would you fire it? Or better question if it was your gun that you assembled and it would not go on a field gauge(5.56) would you fire it?

ETA: I take it back. I just re-read what I wrote. If you knew that it would not go on a 5.56 (Go) and also would not go on a Field either would you shoot it?

[Iraqgunz]

If I used my Field gage, and I knew that I had legit parts and true 5.56 chamber and it failed, I would not shoot it.

In the military when a rifle/carbine fails headspace we replaced the bolt first and re-checked it. If it passed then it was good. If it failed again then it would be re-barreled.

I would suggest that you double check everything and make sure that it is the parts. The easy way to tell is to get another completely assembled upper and barrel and re-test it.


So in your professional opinion (and I was hoping you were one of the ones to answer my question) if I can get a field gauge (5.56) and test it and it won't go on it would you fire it? Or better question if it was your gun that you assembled and it would not go on a field gauge(5.56) would you fire it?

ETA: I take it back. I just re-read what I wrote. If you knew that it would not go on a 5.56 (Go) and also would not go on a Field either would you shoot it?

[number1olddog]

Iraqgunz,

Thanks for your input, it is greatly appreciated. Unfortunately I do not have another legit barrel or upper besides the DPMS and it's BCG. I can however borrow a field gauge tomorrow which I believe should be a 5.56 but unsure of Manufacturer. I cannot however check my chamber to see if it is a legit 5.56 chamber just going off of Sabre's rep in the past as this is my first barrel from that Manufacturer. I am thinking that if I check with a field gauge and it does not go I can test fire it on Saturday with some 855 and see how it goes or I could just send it back to Brownells and get the DD middy barrel that's in stock and probably should have gone that route instead.

[Iraqgunz]

Every company has made bad parts. It's entirely possible that something is wrong with the chamber. This is also one of those times where I hate to diagnose stuff via the net.

I do know that Sabre did have some barrel issues before but they also made quite a few that were perfectly fine.


Iraqgunz,

Thanks for your input, it is greatly appreciated. Unfortunately I do not have another legit barrel or upper besides the DPMS and it's BCG. I can however borrow a field gauge tomorrow which I believe should be a 5.56 but unsure of Manufacturer. I cannot however check my chamber to see if it is a legit 5.56 chamber just going off of Sabre's rep in the past as this is my first barrel from that Manufacturer. I am thinking that if I check with a field gauge and it does not go I can test fire it on Saturday with some 855 and see how it goes or I could just send it back to Brownells and get the DD middy barrel that's in stock and probably should have gone that route instead.

[Clint]

Olddog,

If I'm reading you right, NONE of the gauges would close.

The field is even larger than the no go, so that won't solve anything.

It sounds like your headspace is at or below minimum, especially since the live rounds chambered without issue.

Since you have access to the DPMS BCG, try swapping them and checking headspace on both.

Your chamber/bolt combo may be right at minimum and may pass with a different bolt.

[Todd.K]

I would not shoot a rifle that won't close on the GO gauge. You don't know how much shorter the HS is.

Clean the chamber and gauge very carefully and try again. Try to get a couple of different bolts to check with next.

[Blankwaffe]

See post #13 in thread below.

https://www.m4carbine.net/showthread.php?t=28296&highlight=headspace

[Eric D.]

Good info there.


See post #13 in thread below.

https://www.m4carbine.net/showthread.php?t=28296&highlight=headspace

OP, is your GO gage marked with its actual headspace dimension, IE: 1.4636 or something close to that?

[Blankwaffe]

In my limited experience,if the rifle easily chambers and extracts/ejects rounds normally without issues or damage to the cartridge(i.e. change to COL,leade marking bullet ogive,deformed cartridge shoulder etc.).I call it good to go.

As Bill Alexander detailed expertly in that post I linked,the barrel/bolt combo's Ive had that wouldn't close on a GO,but will chamber rounds without issue, all settle in after a few hundred rounds to near match quality in regards to headspace.I actually prefer a combo a bit on the tight side right out of the box.

That said,if there is doubt always investigate for other issues such as short leade/throat,but if none are found, I'd bet the parts wear into near perfect headspace in regards to the GO gauge.

If it bothers you,and the parts are in spec and no defects,swap bolts around until you get a good match on the GO.

[Clint]

A couple notes on the headspace gauges:

The GO is the shortest. It represents the min length for a new chamber.

The NO GO is 3-6 thou longer than the GO and represents the max length for a new chamber.

A new barrel/bolt that doesn't pass the GO/NO GO check should not leave the factory.

The FIELD is the longest. It is 3 thou longer than the NO GO and represents the maximum limit of serviceability.

A used barrel/bolt that doesn't pass the FIELD check should be removed from service and replaced.

As a barrel/bolt is used, mating surfaces wear in and headspace slowly grows.

The 3 thou difference between the maximum factory check and the field check allows a useful service life for the weapon.

Obviously, an assembly at the upper limit of factory headspace will reach the field limit more quickly than one that started at the lower limit.

It is generally desirable for a new assembly to be just above the min spec.

[number1olddog]

thanks for all the replies Gents. I suppose to just be on the safe side I will send it back for a replacement. It's kind of funny because first the Shield had to go back recently, then another part from Mesa Tactical and now this. Talk about a strange last two months:mad:

[Failure2Stop]

It is also possible to have headspace gauges that are oversized.


Typos brought to you via Tapatalk and autocorrect.

[Clint]

Yes, and sometimes this is purposeful.

A certain well known high end barrel manufacturer, uses graduated sets of headspace gauges.

So instead of a 2 piece set that checks min and max, they use something like a 6 piece set that checks the exact headspace in .0005" increments.

They have a specific target for headspace length and can swap and measure until they hit it.


It is also possible to have headspace gauges that are oversized.


Typos brought to you via Tapatalk and autocorrect.

[K.L. Davis]

Jack and Clint summed it up pretty well... I have had barrels that would not close on a GO gauge from company X, but would close on a gauge from company Z

The pisser is when you check a barrel with an X gauge and it does not close... so you send it back to the manufacturer, who checks it with a Z gauge and says it is fine... 0.0005 is next to nothing, but that much metal will keep you from twisting a bolt closed with you fingers.

Lots of times, when the bolt will not close, you can put an allen wrench or something in the cam pin hole and close it with that little extra mechanical advantage... often it is a little chrome build up in the throat area... or a burr or something... I polish the chambers on every rifle I build and have had many that would not close on the X gauge, then I polish the chamber and all is well... it is impossible to tell you if it is okay or not without having it in hand though.

Bottom line is you have to be comfortable with it... do what it takes to make that so.

[MarkG]

Putting manufacturing tolerances aside, there is no difference in external dimensions between a SAAMI .223 Remington and a Lake City M855 cartidge case. If you believe there is, I would love to see the numbers.

That being said, I'd argue that a headspace gage marked 5.56 NATO is nothing more than marketing 3-Card-Monty. The various chambers are only different in front of the case mouth.

I'm also calling bullshit on any manufacturer or retailer selling a gage that claims to be accurate to ten thousandths. That's an aerospace quality dimension and requires that the gage be manufactured and used at specific temperatures. Truncating the headspace dimensions at a thousandths would have zero impact on safety or function of the weapon.

To accurately gage head space, the barrel has to be removed from the upper receiver and both the extractor and ejector have to be removed from the bolt. It's nothing more than mental masturbation if you aren't.

If you just have to buy a gage and unless you are a barrel manufacturer, IG is correct that a field gage is all you need. A max/reject is preferable but they are hard to find.

[number1olddog]

Fired the weapon today with the "suspect" barrel and all is well. No stuck casings and ejection was as to be expected. Thanks for all the replies from everyone.

[number1olddog]

Ammo used was M855 and my handloads.

[Clint]

Great.

How many rounds did you get through it?

If you're bored, you might want to try rechecking the headspace to see if it passes now.

[Eric D.]

Take a look in the reloading section at the thread titled "Weird things happening with LC brass". I agree there are no differences in exterior dimensions between .223 and 5.56 cases but one poster in that thread points out that a 5.56 NATO chamber has longer headspace limits than a .223 chamber. For my purposes, I consider the maximum HS to be 1.4736, the Colt Field II dimension, for both. I also have a .223 chamber drawing that calls out the max HS as 1.4736.

As to the only differences between the chambers being ahead of the case mouth, it looks like the 5.56 chamber is slightly fatter at the base (Ref C) and the diameter of the chamber 'neck' is slightly larger (Ref F) and the 'neck' length is slightly longer (Ref M).

Picture taken from Luckygunner writeup on .223 vs 5.56
http://i.imgur.com/T9BHb7Z.png


Putting manufacturing tolerances aside, there is no difference in external dimensions between a SAAMI .223 Remington and a Lake City M855 cartidge case. If you believe there is, I would love to see the numbers.

That being said, I'd argue that a headspace gage marked 5.56 NATO is nothing more than marketing 3-Card-Monty. The various chambers are only different in front of the case mouth.

I'm also calling bullshit on any manufacturer or retailer selling a gage that claims to be accurate to ten thousandths. That's an aerospace quality dimension and requires that the gage be manufactured and used at specific temperatures. Truncating the headspace dimensions at a thousandths would have zero impact on safety or function of the weapon.

To accurately gage head space, the barrel has to be removed from the upper receiver and both the extractor and ejector have to be removed from the bolt. It's nothing more than mental masturbation if you aren't.

If you just have to buy a gage and unless you are a barrel manufacturer, IG is correct that a field gage is all you need. A max/reject is preferable but they are hard to find.