AR-15 barrels are self headspacing

golem1961 · 07-23-2007, 10:30 PM

I always hear people say to buy a complete upper to avoid headspace issues and I would like to ask what those issues could possibly be given the fact that AR-15 barrels are self headspacing. There is no adjustment that you can make that will impact headspacing in an AR-15. The only issue that can be addressed by the amount of torque one puts on a barrel/upper receiver combination is whether or not you have a good seat or if you are stripping the threads. The correct amount of torque on the barrel nut is 50 ftpounds. The only thing you have to remember besides that is when aligning the barrel nut with the gas tube opening is to tighten not loosen. I have built ARs for over twenty years and I was tutored by a retired COLT assembler and I'm sure of this information. I hope this helps.

Beer Forever · 07-23-2007, 11:17 PM

That is interesting. I haven't worried too much about head spacing because of the fact that I always get complete uppers, but only because I have found a few really killer deals.

Pred · 07-24-2007, 06:27 PM

It's very, VERY rare that you would get a problem with headspacing on an AR. I have no problem buying an upper(from a good company) and a bolt(from another good company), slapping it together, and taking it right to the range. The AR is a lot like the old Mosin's, in the sense that most any part from most any gun will work in any AR.

lefty o · 07-24-2007, 07:12 PM

i wouldnt go so far as to say ar barrels are self headspacing, cuz it aint so. now because of modern machining, your odds of putting one together and getting correct headspace is pretty good, but not guaranteed. unless of course the pre-chambered barrel you purchased also comes with matching bolt. without a set of guages, you can not guarantee your headspace is in spec. never assume anything.

samuel · 07-24-2007, 08:17 PM

Correct!!!Because the housing is aluminum the bolt lugs must be locked into the steel breech.But with multiple companys making bolts and barrels they should be checked with guages. sam.

golem1961 · 07-25-2007, 12:04 AM

I agree that a go and or no go guage should be used when assembling any upper I am just stating that if you get a no go, there is nothing you can do about it except to swap out the barrel or check the bolt for defects. there is no adjustment that you can make to bring it into spec. the locking lugs are machined into the barrel and that determines the headspace, therefore, it matters not whether the upper was assembled by Colt, Dpms, Bushmaster, etc. or Bubba in his garage. as long as the barrel is seated headspace will not be affected. I know this is probably a hot button issue for some, however I have seen multiple posts from people perpetuating the myth that headspacing can be affected by the manner in which the upper is assembled and that just isnt true. Seat the barrel, torque the barrel nut to 50 ftpounds, and remember to tighten, not loosen to align the gastube and you will never go wrong. If for same reason you have a headspacing issue, send the barrel or bolt back for a replacement.

lefty o · 07-25-2007, 05:14 AM

i think you just need to state what your saying differently. when your dealing with a chrome lined barrel, all you can do is swap bolts and see if you get lucky. with a non lined barrel, as long as the headspace is short, you still have options. might state that chrome lined barrels have non adjustable headspace, instead of self headspacing.

golem1961 · 07-25-2007, 09:46 PM

all I,m saying is that you can not affect headspace by barreling an ar15 upper receiver

lefty o · 07-26-2007, 09:50 AM

but that doesnt mean that it is going to headspace correctly when you slap the parts together. thats all im saying!

Big Dog · 07-26-2007, 06:32 PM

Boys . . . boys . . . please, can't we all just get along?

Beer Forever · 07-26-2007, 07:35 PM

My car is cooler than your car

Some things just don't change.

lefty o · 07-26-2007, 09:47 PM

we are getting along. not a harsh word has been said.

Big Dog · 07-27-2007, 04:42 AM

"More filling!"
"Tastes great!"

Just trying to keep it civil, got my Moderator Hat on . . .

That's one thing great about the Little Black Rifle - ease of assembly! Even more so than the vaunted AK.

samuel · 07-27-2007, 05:28 AM

Headspacing is misunderstood by most.A proper headspacing will not go over .006" and the magic # is .003" The same as Ezaerln stated with the BMG.50.In auto-loaders it may be over .003" but in most cases isnt.If you go under .003" you may find you cant shoot some brands of ammo or neck resize.This goes for any type of action.They have come up with what they call "field size" guages which means you can close the action on rhe "no go" guage but not on the "field" guage.This means you can fire factory cartridges safely but probably wont be able to resize so reloads will chamber.Believe it or not,full resizing does not bring a casing back to original specs.With a "field" headspacing you can reload by using a collet neck resizing die.You just cant chamber those cartridges in any other gun.This is why LeftyO says the headspace might not be right.If you have too much headspace as long as it isnt over .006" they will work but they may be hard to resize.If you are under .003 you may and probably will have chambering problems.Some brands may chamber but others wont. sam.

JoeLee · 07-27-2007, 08:40 AM

golem1961,I had this on file I hope it helps.
-------------------------------------------------
The current military specifications for the M16 series call for headspace of not less than 1.4646” and not more than 1.4706” on a new rifle. The commercial Forster/SAAMI gauges are marked in 1,000ths of an inch instead the 10,000ths of an inch that the dedicated M16 gauges are. When installing a new barrel, the commercial gauge measuring 1.465" can be used in place of the M16 "Go" gauge. Consider the 4/10,000ths of an inch difference an extra margin of safety. The commercial 1.470" gauge (the commercial "Field" gauge) can be used to confirm that the headspace is within spec for a new rifle. Unfortunately, there are no gauges available to measure between 1.470" and 1.4730", the latter being the measurement on the M16 "Field" gauge.

The M16 Field Service gauge measures a dimension of greater than 1.4730”. A rifle with a bolt that does not close on a Field Service gauge is considered safe to fire by the army, but not the Marines who use the military "No-Go" gauge for that measurement. Without using military Go or No-Go gauges, or commercial gauges marked with their measurements, you cannot know whether or not it is truly in spec. An interesting tidbit of information is that the Colt M16/AR15 Field gauge measures a dimension in excess of 1.4736”. It seems that the military has built in a bit more of a safety factor with their gauge.

You should remove the extractor parts and the ejector, which normally requires four hands. Removing the ejector is a two-handed job if you have the proper tools, specifically a Sinclair Bolt Vice for the AR15.

You can’t really reset the headspace on an AR15 with a chrome-lined chamber. That is set when the barrel extension is installed on the barrel. If you have an unlined barrel, with short headspace, a gunsmith can adjust it by cutting the chamber deeper with the appropriate chambering reamers. If the headspace is long, or the chamber chrome-lined, the only option is to try a different bolt until headspace checks good, or you run out of bolts. Then it is time for a new barrel.

To recap, the specs are as follows:

New Rifle Headspace: 1.4646" to 1.4706"
SAMMI headspace gauges to use: 1.465" and 1.470"

Unsafe Rifle Headspace: 1.4736"
Use the Colt M16/AR15 Field Gauge: 1.4736" or,
The US military gauge: 1.4730”

Note: The Forster/SAAMI "No-Go" gauge measures 1.467"

Sources for Gauges -
Brownells: www.Brownells.com SAAMI gauges and a whole lot of new AR15 parts and accessories.
Sarco: www.sarcoinc.com Military “Field” gauge as well as other maintenance items and M16/AR15 parts and accessories.

samuel · 07-27-2007, 08:58 AM

Thanks for looking all of the specs up and the info on where to get guages.Often headspace is the cause of problems in not only AR type but any type of action.Again thanks. sam.

golem1961 · 07-27-2007, 11:55 PM

Okay, how about this. Anyone that can change the headspace on an AR15 by attaching it to a receiver tell me how. You can't rechamber the barrel, you can only attach it to the receiver. Can you do it?

07-23-2007, 10:30 PM	#1
golem1961 Member Join Date: Feb 2007 Location: Woodville tx. Vienna Il. Posts: 73 Trader Rating: (0)	AR-15 barrels are self headspacing I always hear people say to buy a complete upper to avoid headspace issues and I would like to ask what those issues could possibly be given the fact that AR-15 barrels are self headspacing. There is no adjustment that you can make that will impact headspacing in an AR-15. The only issue that can be addressed by the amount of torque one puts on a barrel/upper receiver combination is whether or not you have a good seat or if you are stripping the threads. The correct amount of torque on the barrel nut is 50 ftpounds. The only thing you have to remember besides that is when aligning the barrel nut with the gas tube opening is to tighten not loosen. I have built ARs for over twenty years and I was tutored by a retired COLT assembler and I'm sure of this information. I hope this helps. __________________ Beyond Tactical, Practical!

07-23-2007, 11:17 PM	#2
Beer Forever Senior Member Join Date: Dec 2005 Location: Tucson, AZ Posts: 2,693 Trader Rating: (0)	That is interesting. I haven't worried too much about head spacing because of the fact that I always get complete uppers, but only because I have found a few really killer deals. __________________ Paramedic sks forever Last edited by Beer Forever; 07-24-2007 at 09:03 PM.

07-24-2007, 08:17 PM	#5
samuel Senior Member Join Date: Dec 2006 Posts: 5,050 Trader Rating: (0)	Correct!!!Because the housing is aluminum the bolt lugs must be locked into the steel breech.But with multiple companys making bolts and barrels they should be checked with guages. sam. Last edited by samuel; 07-24-2007 at 08:24 PM.

07-25-2007, 12:04 AM	#6
golem1961 Member Join Date: Feb 2007 Location: Woodville tx. Vienna Il. Posts: 73 Trader Rating: (0)	I agree that a go and or no go guage should be used when assembling any upper I am just stating that if you get a no go, there is nothing you can do about it except to swap out the barrel or check the bolt for defects. there is no adjustment that you can make to bring it into spec. the locking lugs are machined into the barrel and that determines the headspace, therefore, it matters not whether the upper was assembled by Colt, Dpms, Bushmaster, etc. or Bubba in his garage. as long as the barrel is seated headspace will not be affected. I know this is probably a hot button issue for some, however I have seen multiple posts from people perpetuating the myth that headspacing can be affected by the manner in which the upper is assembled and that just isnt true. Seat the barrel, torque the barrel nut to 50 ftpounds, and remember to tighten, not loosen to align the gastube and you will never go wrong. If for same reason you have a headspacing issue, send the barrel or bolt back for a replacement. __________________ Beyond Tactical, Practical!

07-25-2007, 09:46 PM	#8
golem1961 Member Join Date: Feb 2007 Location: Woodville tx. Vienna Il. Posts: 73 Trader Rating: (0)	all I,m saying is that you can not affect headspace by barreling an ar15 upper receiver __________________ Beyond Tactical, Practical! Last edited by golem1961; 07-25-2007 at 10:16 PM.

07-24-2007, 06:27 PM	#3
Pred Banned Join Date: Aug 2005 Location: Kentucky Posts: 3,873 Trader Rating: (0)	It's very, VERY rare that you would get a problem with headspacing on an AR. I have no problem buying an upper(from a good company) and a bolt(from another good company), slapping it together, and taking it right to the range. The AR is a lot like the old Mosin's, in the sense that most any part from most any gun will work in any AR.

07-24-2007, 07:12 PM	#4
lefty o Senior Member Join Date: Mar 2002 Location: mn Posts: 4,672 Trader Rating: (0)	i wouldnt go so far as to say ar barrels are self headspacing, cuz it aint so. now because of modern machining, your odds of putting one together and getting correct headspace is pretty good, but not guaranteed. unless of course the pre-chambered barrel you purchased also comes with matching bolt. without a set of guages, you can not guarantee your headspace is in spec. never assume anything.

07-25-2007, 05:14 AM	#7
lefty o Senior Member Join Date: Mar 2002 Location: mn Posts: 4,672 Trader Rating: (0)	i think you just need to state what your saying differently. when your dealing with a chrome lined barrel, all you can do is swap bolts and see if you get lucky. with a non lined barrel, as long as the headspace is short, you still have options. might state that chrome lined barrels have non adjustable headspace, instead of self headspacing.

07-26-2007, 09:50 AM	#9
lefty o Senior Member Join Date: Mar 2002 Location: mn Posts: 4,672 Trader Rating: (0)	but that doesnt mean that it is going to headspace correctly when you slap the parts together. thats all im saying!

07-26-2007, 06:32 PM	#10
Big Dog Moderator Join Date: Mar 2002 Location: Tallahassee, Florida Posts: 10,020 Trader Rating: (0)	Boys . . . boys . . . please, can't we all just get along? __________________ Moderator of: AR15/M16, M14/M1A, New/Beginning Shooters and Militaria/Collectables.

07-26-2007, 07:35 PM	#11
Beer Forever Senior Member Join Date: Dec 2005 Location: Tucson, AZ Posts: 2,693 Trader Rating: (0)	My car is cooler than your car Some things just don't change. __________________ Paramedic sks forever

07-26-2007, 09:47 PM	#12
lefty o Senior Member Join Date: Mar 2002 Location: mn Posts: 4,672 Trader Rating: (0)	we are getting along. not a harsh word has been said.

07-27-2007, 04:42 AM	#13
Big Dog Moderator Join Date: Mar 2002 Location: Tallahassee, Florida Posts: 10,020 Trader Rating: (0)	"More filling!" "Tastes great!" Just trying to keep it civil, got my Moderator Hat on . . . That's one thing great about the Little Black Rifle - ease of assembly! Even more so than the vaunted AK. __________________ Moderator of: AR15/M16, M14/M1A, New/Beginning Shooters and Militaria/Collectables.

07-27-2007, 05:28 AM	#14
samuel Senior Member Join Date: Dec 2006 Posts: 5,050 Trader Rating: (0)	Headspacing is misunderstood by most.A proper headspacing will not go over .006" and the magic # is .003" The same as Ezaerln stated with the BMG.50.In auto-loaders it may be over .003" but in most cases isnt.If you go under .003" you may find you cant shoot some brands of ammo or neck resize.This goes for any type of action.They have come up with what they call "field size" guages which means you can close the action on rhe "no go" guage but not on the "field" guage.This means you can fire factory cartridges safely but probably wont be able to resize so reloads will chamber.Believe it or not,full resizing does not bring a casing back to original specs.With a "field" headspacing you can reload by using a collet neck resizing die.You just cant chamber those cartridges in any other gun.This is why LeftyO says the headspace might not be right.If you have too much headspace as long as it isnt over .006" they will work but they may be hard to resize.If you are under .003 you may and probably will have chambering problems.Some brands may chamber but others wont. sam.

07-27-2007, 08:40 AM	#15
JoeLee Banned Join Date: Apr 2007 Location: North New York State. Posts: 1,241 Trader Rating: (0)	golem1961,I had this on file I hope it helps. ------------------------------------------------- The current military specifications for the M16 series call for headspace of not less than 1.4646” and not more than 1.4706” on a new rifle. The commercial Forster/SAAMI gauges are marked in 1,000ths of an inch instead the 10,000ths of an inch that the dedicated M16 gauges are. When installing a new barrel, the commercial gauge measuring 1.465" can be used in place of the M16 "Go" gauge. Consider the 4/10,000ths of an inch difference an extra margin of safety. The commercial 1.470" gauge (the commercial "Field" gauge) can be used to confirm that the headspace is within spec for a new rifle. Unfortunately, there are no gauges available to measure between 1.470" and 1.4730", the latter being the measurement on the M16 "Field" gauge. The M16 Field Service gauge measures a dimension of greater than 1.4730”. A rifle with a bolt that does not close on a Field Service gauge is considered safe to fire by the army, but not the Marines who use the military "No-Go" gauge for that measurement. Without using military Go or No-Go gauges, or commercial gauges marked with their measurements, you cannot know whether or not it is truly in spec. An interesting tidbit of information is that the Colt M16/AR15 Field gauge measures a dimension in excess of 1.4736”. It seems that the military has built in a bit more of a safety factor with their gauge. You should remove the extractor parts and the ejector, which normally requires four hands. Removing the ejector is a two-handed job if you have the proper tools, specifically a Sinclair Bolt Vice for the AR15. You can’t really reset the headspace on an AR15 with a chrome-lined chamber. That is set when the barrel extension is installed on the barrel. If you have an unlined barrel, with short headspace, a gunsmith can adjust it by cutting the chamber deeper with the appropriate chambering reamers. If the headspace is long, or the chamber chrome-lined, the only option is to try a different bolt until headspace checks good, or you run out of bolts. Then it is time for a new barrel. To recap, the specs are as follows: New Rifle Headspace: 1.4646" to 1.4706" SAMMI headspace gauges to use: 1.465" and 1.470" Unsafe Rifle Headspace: 1.4736" Use the Colt M16/AR15 Field Gauge: 1.4736" or, The US military gauge: 1.4730” Note: The Forster/SAAMI "No-Go" gauge measures 1.467" Sources for Gauges - Brownells: www.Brownells.com SAAMI gauges and a whole lot of new AR15 parts and accessories. Sarco: www.sarcoinc.com Military “Field” gauge as well as other maintenance items and M16/AR15 parts and accessories.

07-27-2007, 08:58 AM	#16
samuel Senior Member Join Date: Dec 2006 Posts: 5,050 Trader Rating: (0)	Thanks for looking all of the specs up and the info on where to get guages.Often headspace is the cause of problems in not only AR type but any type of action.Again thanks. sam.

07-27-2007, 11:55 PM	#17
golem1961 Member Join Date: Feb 2007 Location: Woodville tx. Vienna Il. Posts: 73 Trader Rating: (0)	Okay, how about this. Anyone that can change the headspace on an AR15 by attaching it to a receiver tell me how. You can't rechamber the barrel, you can only attach it to the receiver. Can you do it? __________________ Beyond Tactical, Practical! Last edited by golem1961; 07-28-2007 at 12:13 AM.