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Posted: 9/8/2013 11:03:48 AM EDT
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Have finished up my 1st AR build, using a Lilja AR24 barrel.
I have the following Forster headspace gauges- .14636"- bolt closes satisfactorily/easily. .14736"- bolt will NOT close. Ejector pin removed, extractor in place. (Is the extractor also supposed to be removed? I thought just the pin, but just read somewhere about someone also removing the extractor as well) Is this good to go???I thought the bolt should close- but be tough to close on the .14736" gauge?? Thanks for the help/advice Wes |
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A little further thought into this- and re-reading the instructions that came with the gauges I realize the longer one should indeed not close.... that would be an indication of excessive headspace. Would like, however- to confirm the dimensions for these go/no-go gauges though...
Extractor in or out?? Wes |
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I believe both the ejector and extractor should be removed.
Optimally the bolt face should make contact with the base of the gauge. Both extractor and ejector have springs associated with them. It is a matter of feel to a certain degree. Trying to push the extractor over the rim of the gauge gives a false "feel". The extractor is easy to remove compared to the ejector, so take it out. Just my opinion. |
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Quoted:
Have finished up my 1st AR build, using a Lilja AR24 barrel. I have the following Forster headspace gauges- .14636"- bolt closes satisfactorily/easily. .14736"- bolt will NOT close. Ejector pin removed, extractor in place. (Is the extractor also supposed to be removed? I thought just the pin, but just read somewhere about someone also removing the extractor as well) Is this good to go???I thought the bolt should close- but be tough to close on the .14736" gauge?? Thanks for the help/advice Wes I have two videos that cover proper head spacing on an AR-15. The first one is without the barrel installed and the second is with. Please feel free to view them. The general opinion is that if you buy your barrel from a reputable manufacturer, you probably don't have to check head space. On an uninstalled barrel: 
On an installed barrel:
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not trying to hijack, but to add to this question, which headspace gauges are needed to confirm all is well on AR builds? Should a person buy just the go/no go gauges in 223 remington or 5.56 or both? Should a field gauge be used as well?
I'm looking into doing a few builds, and I know most people will say that they aren't needed, but I'd prefer to be cautious and purchase the gauges that I need to check properly. Thanks in advance. |
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not trying to hijack, but to add to this question, which headspace gauges are needed to confirm all is well on AR builds? Should a person buy just the go/no go gauges in 223 remington or 5.56 or both? Should a field gauge be used as well? I'm looking into doing a few builds, and I know most people will say that they aren't needed, but I'd prefer to be cautious and purchase the gauges that I need to check properly. Thanks in advance. Headspace is measured from the bolt face to the datum line of the chamber; therefore, you purchase the correct gauges based on the round your chamber is cut for when dealing with 5.56 NATO vs. .223 Remington. So, if your barrel is an actual 5.56 chamber; check headspace using 5.56 gauges. And, use .223 gauges if your barrel is setup for .223 Remington rounds. The two mil-specifications below, one for the rifle and other for the carbine, have a section in each mil-spec on checking headspace for an unfired bolt/barrel combination. A go gauge checks the minimum safe headspace, a no-go gauge checks maximum headspace for an unfired barrel, and a field gauge checks maximum allowable headspace for a used barrel. MIL-C-71186 / M4 Carbine http://www.biggerhammer.net/ar15/milspec/MIL-C-71186_(AR).pdf MIL-R-71135 / M16A2E3 http://www.everyspec.com/MIL-SPECS/MIL-SPECS-MIL-R/download.php?spec=MIL-R-71135.011740.PDF ArmaLite Tech Note 60: Measuring Headspace http://www.armalite.com/images/Tech%20Notes%5CTech%20Note%2060,%20Measuring%20Headspace%20040113.pdf SAAMI: 5.56 NATO vs .223 Remington http://www.thegunzone.com/556v223.html |
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My understanding was that 5.56 and 223 GO headspace gauges were the same length, and the NO GO gauges between the calibers were different.
A 5.56 will close on a 223 no go gauge but not a 5.56 no go. So it seems to me that the gauges to have on hand would be a 223 go gauge, a 223 and 556 no go gauge, and a colt field gauge. Does this seem correct? or should one just have on hand a 223 go/no go set and the field gauge to check everything? |
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The gages are the same for 223 REM or 5.56 min and max headspace.
The trick is with a new barrel a person does not want it starting with too much headspace and opinions vary on how much that should be. AFAIK the current 5.56 No Go gage is 1.4706 inches and a SAAMI spec 223 REM No Go gage is 1.4666 inches. Personally at the prices we pay for barrels I would not find 70% of the headspace gone before the first shot acceptable (5.56 No Go). Fortunately I have not received any 5.56 barrels that failed the 1.4676 inch gage. |
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How are the min and maximum gauges the same? The measurements are not even the same; that would be like saying the number 1 is also the number 2.
Gauge GO NO-GO FIELD FIELD II Civilian 1.4640" 1.4670" 1.4700" 1.4736" Military 1.4646" 1.4706" 1.4730" N/A http://www.ar15barrels.com/data/headspace.pdf MIL-C-71186 http://www.biggerhammer.net/ar15/milspec/MIL-C-71186_(AR).pdf 3.4.1 Headspace. The headspace shall not be less than 1.4646 inches nor more than 1.4706 inches when measured to the .330 inch datum diameter on the first shoulder of the chamber. Headspace for carbines fired with 30 round magazines shall be measured and recorded at the beginning of the test and at the completion of the 50th cycle. After the 50th cycle, the headspace shall not be more than .0028 inch greater than the initial measurement and shall not exceed .0024 inch over maximum. MIL-R-71135 http://www.everyspec.com/MIL-SPECS/MIL-SPECS-MIL-R/download.php?spec=MIL-R-71135.011740.PDF 3.4.1 Headspace. The head space shall not be less than 1.4646 inches nor more than 1.4706 inches when measured to the .330 inch datum diameter on the first shoulder of the chamber. Headspace for rifles being fired with 30 round maqazines shall be measured and recorded at the begihing o~ the test and at the completion of the 50th cycle using inspection equipment per drawing 8440878. After the 50th cycle, the headspace shall not be more than .0028 inch greater than the Initial measurement and shall not exceed .0024 inch over maximum. |
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Military I am good with your find, but there are NATO marked gages out there marked 1.4636.
I have seen NATO marked gages for max chamber at 1.4736. The last time I looked the SAAMI site 223 REM chamber drawing showed 1.4636 min and 1.4736 max. I also believe you can find 223 REM No Go gages marked 1.4666. I have a set of 223 REM gages marked with your first three civilian measurements I bought more than 30 years ago. I also have a current 223 REM match gage set that starts at 1.4636 and goes to 1.4736 in .001 increments. So we currently have a regular smorgasbord of gages with conflicting measurements floating around. Do you think a barrel that fails the 1.4646 gage and passes a 1.4636 gage is unsafe to fire? At this point in time I see more questions than answers. |
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Military I am good with your find, but there are NATO marked gages out there marked 1.4636. I have seen NATO marked gages for max chamber at 1.4736. The last time I looked the SAAMI site 223 REM chamber drawing showed 1.4636 min and 1.4736 max. I also believe you can find 223 REM No Go gages marked 1.4666. I have a set of 223 REM gages marked with your first three civilian measurements I bought more than 30 years ago. I also have a current 223 REM match gage set that starts at 1.4636 and goes to 1.4736 in .001 increments. So we currently have a regular smorgasbord of gages with conflicting measurements floating around. Do you think a barrel that fails the 1.4646 gage and passes a 1.4636 gage is unsafe to fire? At this point in time I see more questions than answers. The SAAMI drawing for .223 REM is 21 years old; ANSI/SAAMI Centerfire Rifle | Z.299.4 1992 <~~ (21 years ago) http://www.saami.org/specifications_and_information/index.cfm?page=CC |
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Researching the issue further, being that .223 REM is based off of SAAMI Specifications, by the research were setup initially for bolt-action rifles chambered for .223 REM. For a .223 REM match headspace set; 1.4666 to 1.4736 is what SAAMI allows the cartridge to be between breech face and .330 datum line; hence the measurement on the blueprint 1.4666 - .0070. We will find if we add 1.4666 + .0070, it equals 1.4736.
For SAAMI headspace measurements, they allow a minimum of 1.4636 to a maximum of 1.4736 from breech face to .330 datum line. Both MIL-C-71186 and MIL-R-71135 set headspace between a minimum of 1.4646" to a maximum of 1.4706". But, after the 50th cycle for a new barrel they only allow the headspace to increase by .0028" from the initial measurement, and shall not exceed .0024" over the maximum. And, wouldn't you know if we add 1.4706" + .0024" it will equal 1.4730. Howbeit, 1.4730" is the military's field gauge's measurment. Then, if we look at the Colt II Field Gauge; wouldn't we know, its measurement equals 1.4736. As for the No-go gauges, comparing SAAMI with the military's; it is noteworthy to see the military sets its No-go to be 10 thousandths of an inch looser (.001") {1.4646 versus 1.4636} than the SAAMI measurment. I wonder why the military wants an additional thousandth of an inch??? But, I guess the numbers Eugene Stoner set for the AR-15 are wrong; OH WELL! SAAMI Cartridge and Chamber Blueprint http://www.saami.org/pubresources/cc_drawings/Rifle/223%20Remington.pdf |
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The military needs reliable weapons in battlefield environments where maintenance has been less than ideal. I am not surprised they would spec 1.4646 for Go, if anything the surprise is that it is that tight. SAAMI allows the chamber to be as tight as 1.4636 versus the military only allows it to be as tight as 1.4646", which is looser than 1.4636 by .001 or 1 thousandths of an inch. How is the military's minimum headspace then tighter than SAAMI's minimum headspace? |
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Your comment did imply it, being your response was based off the information I presented; which is sourced, so it cannot be claimed as erroneous or opinionated being based off the actual military specifications for the rifle and carbine and SAAMI .223 REM cartridge/chamber dimensions. The facts are the facts nevertheless that the military only allows chambers as tight as 1.4646 which is one thousandth of an inch looser than a SAAMI spec'd chamber. Unless .223 REM and 5.56 NATO do not use the same cartridge outer dimensions??? Clearly they do.
If you or anyone else can read and can count; it adds up. |
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This is the first time ever I have been able to imply the opposite of what I said, imagine that.
I am getting you love the mil-spec? The math of the 1.4706” gage plus the fifty round test has not passed me by. Of course my take is that means the military could get weapons that have very little headspace left before failing the field gage. I am sure that is great for the military, but as a civilian my expectations are somewhat tighter than that for the barrels I buy. |
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This is the first time ever I have been able to imply the opposite of what I said, imagine that. I am getting you love the mil-spec? The math of the 1.4706” gage plus the fifty round test has not passed me by. Of course my take is that means the military could get weapons that have very little headspace left before failing the field gage. I am sure that is great for the military, but as a civilian my expectations are somewhat tighter than that for the barrels I buy. The mil-spec is more specific than that (its a worthy read; the entire specification that is), after the 50th cycle not 50th round for a new barrel they only allow the headspace to increase by .0028" from the initial measurement, and shall not exceed .0024" over the maximum. Which obviously it's a given that the initial measurement will vary from one chamber to the other due to machining and tolerances. Also, 1 cycle for the 50 cycle endurance test equals twenty 30 round magazines; making 600 rounds equal to 1 cycle. Therefore, the 50th cycle equals 30,000 rounds. An almost 3 thousandths of an inch increase in headspace from the initial measurement after 30,000 rounds doesn't seem extreme to me by the round count achieved. Also, clearly you wouldn't use a Ford Factory Repair Manual for specifications of a General Motors Engine right? So, if you are going to maintain an AR-15, why would you disregard the measurements that was specified for the weapon? Whether a citizen uses an AR-15 or a citizen-soldier uses a M-16/M-4; both their cartridges outer dimensions are the same. Which leads me to ask why do you prefer the minimum headspace to be 1 thousandth of an inch tighter going off a SAAMI Go gauge versus 1 thousandth of an inch looser with the military's Go gauge? |
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The mil-spec is more specific than that (its a worthy read; the entire specification that is), after the 50th cycle not 50th round for a new barrel they only allow the headspace to increase by .0028" from the initial measurement, and shall not exceed .0024" over the maximum. Which obviously it's a given that the initial measurement will vary from one chamber to the other due to machining and tolerances. Also, 1 cycle for the 50 cycle endurance test equals twenty 30 round magazines; making 600 rounds equal to 1 cycle. Therefore, the 50th cycle equals 30,000 rounds. An almost 3 thousandths of an inch increase in headspace from the initial measurement after 30,000 rounds doesn't seem extreme to me by the round count achieved. Also, clearly you wouldn't use a Ford Factory Repair Manual for specifications of a General Motors Engine right? So, if you are going to maintain an AR-15, why would you disregard the measurements that was specified for the weapon? Whether a citizen uses an AR-15 or a citizen-soldier uses a M-16/M-4; both their cartridges outer dimensions are the same. Which leads me to ask why do you prefer the minimum headspace to be 1 thousandth of an inch tighter going off a SAAMI Go gauge versus 1 thousandth of an inch looser with the military's Go gauge? Quoted:
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This is the first time ever I have been able to imply the opposite of what I said, imagine that. I am getting you love the mil-spec? The math of the 1.4706” gage plus the fifty round test has not passed me by. Of course my take is that means the military could get weapons that have very little headspace left before failing the field gage. I am sure that is great for the military, but as a civilian my expectations are somewhat tighter than that for the barrels I buy. The mil-spec is more specific than that (its a worthy read; the entire specification that is), after the 50th cycle not 50th round for a new barrel they only allow the headspace to increase by .0028" from the initial measurement, and shall not exceed .0024" over the maximum. Which obviously it's a given that the initial measurement will vary from one chamber to the other due to machining and tolerances. Also, 1 cycle for the 50 cycle endurance test equals twenty 30 round magazines; making 600 rounds equal to 1 cycle. Therefore, the 50th cycle equals 30,000 rounds. An almost 3 thousandths of an inch increase in headspace from the initial measurement after 30,000 rounds doesn't seem extreme to me by the round count achieved. Also, clearly you wouldn't use a Ford Factory Repair Manual for specifications of a General Motors Engine right? So, if you are going to maintain an AR-15, why would you disregard the measurements that was specified for the weapon? Whether a citizen uses an AR-15 or a citizen-soldier uses a M-16/M-4; both their cartridges outer dimensions are the same. Which leads me to ask why do you prefer the minimum headspace to be 1 thousandth of an inch tighter going off a SAAMI Go gauge versus 1 thousandth of an inch looser with the military's Go gauge? My bad. However the mil-spec I did read showed 120 rds as a cycle. I don’t necessarily prefer min headspace, but I do think it is safe. I like the headspace tight (pass a 1.4656” gage) on a rifle I am trying to get MOA or better from. I like SHTF/SD/HD weapons a little looser. |
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I had my headspace checked at a shop and I believe they only checked the go gage (which means the bolt will close on a round). Is there any other indication of excessive headspace besides usingf a gauge? Popping primers, a lot of smoke coming out of the wrong end of the weapon?? Gages are the sure fire way and gages are not that expensive if one considers the potential downside. I have seen a number of posts where experienced people did not know they had a weapon problem because they thought it was the ammo. |
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My bad. However the mil-spec I did read showed 120 rds as a cycle. I don’t necessarily prefer min headspace, but I do think it is safe. I like the headspace tight (pass a 1.4656” gage) on a rifle I am trying to get MOA or better from. I like SHTF/SD/HD weapons a little looser. Quoted:
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This is the first time ever I have been able to imply the opposite of what I said, imagine that. I am getting you love the mil-spec? The math of the 1.4706” gage plus the fifty round test has not passed me by. Of course my take is that means the military could get weapons that have very little headspace left before failing the field gage. I am sure that is great for the military, but as a civilian my expectations are somewhat tighter than that for the barrels I buy. The mil-spec is more specific than that (its a worthy read; the entire specification that is), after the 50th cycle not 50th round for a new barrel they only allow the headspace to increase by .0028" from the initial measurement, and shall not exceed .0024" over the maximum. Which obviously it's a given that the initial measurement will vary from one chamber to the other due to machining and tolerances. Also, 1 cycle for the 50 cycle endurance test equals twenty 30 round magazines; making 600 rounds equal to 1 cycle. Therefore, the 50th cycle equals 30,000 rounds. An almost 3 thousandths of an inch increase in headspace from the initial measurement after 30,000 rounds doesn't seem extreme to me by the round count achieved. Also, clearly you wouldn't use a Ford Factory Repair Manual for specifications of a General Motors Engine right? So, if you are going to maintain an AR-15, why would you disregard the measurements that was specified for the weapon? Whether a citizen uses an AR-15 or a citizen-soldier uses a M-16/M-4; both their cartridges outer dimensions are the same. Which leads me to ask why do you prefer the minimum headspace to be 1 thousandth of an inch tighter going off a SAAMI Go gauge versus 1 thousandth of an inch looser with the military's Go gauge? My bad. However the mil-spec I did read showed 120 rds as a cycle. I don’t necessarily prefer min headspace, but I do think it is safe. I like the headspace tight (pass a 1.4656” gage) on a rifle I am trying to get MOA or better from. I like SHTF/SD/HD weapons a little looser. I reread the information and just realized I misread the information; 6,000 rounds equals 50 cycles which based off the 120 rounds a cycle; an increase in headspace by .0028" from the initial measurement is still a small increase off the round count of 6,000 rounds. |
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I have two videos that cover proper head spacing on an AR-15. The first one is without the barrel installed and the second is with. Please feel free to view them. The general opinion is that if you buy your barrel from a reputable manufacturer, you probably don't have to check head space. On an uninstalled barrel:  http://youtu.be/-fJbezHgGBA
On an installed barrel: http://youtu.be/IWTpPMYW-CASince nobody else did, I'll say thanks the video links! |
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