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Posted: 8/31/2012 3:45:41 PM EDT
| I just finished building my first AR build. I was attempting to check the headspace using the Brownells "Go" and "No Go" Headspace Gauges. The bolt closes on both gauges and I'm not sure what that means. I assumed the bolt would close on the "go" gauge and not on the "no go" gauge. Any information on if me firearm is safe to shoot and how do I fix the headspace if needed. |
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I just finished building my first AR build. I was attempting to check the headspace using the Brownells "Go" and "No Go" Headspace Gauges. The bolt closes on both gauges and I'm not sure what that means. I assumed the bolt would close on the "go" gauge and not on the "no go" gauge. Any information on if me firearm is safe to shoot and how do I fix the headspace if needed. You'll have to specify the length marked on these gauges for anyone to be able to comment. |
| Which soecific gauges are you using? Brownells sells a number of different headsoace gauges, so as DirectDrive mentioned, we'd need to know what their specified lengths were. Also, did you follow the instructions with the gauges exactly? That makes a big difference. |
| The gauges are both Clymer gauges. The "Go" gauge is 5.56 NATO and measures 1.4696" and the "No Go" gauge is 5.56 NATO and measures 1.4636". They didn't come with any directions. I removed the extractor, reinserted the complete bolt and bolt carrier minus the extractor, extractor spring and roll pin and tried both gauges out 1 at a time and the bolt closes with finger pressure. If I'm doing this wrong or missed something please let me know. |
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The gauges are both Clymer gauges. The "Go" gauge is 5.56 NATO and measures 1.4696" and the "No Go" gauge is 5.56 NATO and measures 1.4636". They didn't come with any directions. I removed the extractor, reinserted the complete bolt and bolt carrier minus the extractor, extractor spring and roll pin and tried both gauges out 1 at a time and the bolt closes with finger pressure. If I'm doing this wrong or missed something please let me know. I realize it's late but how can the "No Go" gauge be smaller than the go? I've been doing this machinist thing for 25 years and 1.4636 IS less than 1.4696. If this is a steel tool that mimics a cartridge case and the "go" is longer than the "no go" then something is wrong. |
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The gauges are both Clymer gauges. The "Go" gauge is 5.56 NATO and measures 1.4696" and the "No Go" gauge is 5.56 NATO and measures 1.4636". They didn't come with any directions. I removed the extractor, reinserted the complete bolt and bolt carrier minus the extractor, extractor spring and roll pin and tried both gauges out 1 at a time and the bolt closes with finger pressure. If I'm doing this wrong or missed something please let me know. The "NO GO" gauge should be the longer one. And you need to take out the EJECTOR, not just the extractor. Since you mention the roll pin, maybe you did that, but maybe not. My gauges are Forster's, but basically the same thing, and yours should work properly with a good chamber. |
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I guess with all gauges you need to remove the extractor, etc, for them to work correctly. Is there no other way other than to check it with a gauge of some sort? There are gauges which are machined to allow checking headspace without disassembling the bolt. Since the headspace is defined by face of the bolt and the shoulder of the chamber, no, there is no other way to accurately check headspace than with a gauge. Guns will often headspace differently even with two brand-new bolts, owing to minute tolerance changes in mass-manufactured parts - though it's extremely rare for new parts to be so out of tolerance as to be dangerous. |
| There are three headspace gauges, go, no go, and field. Go gauge measures the minimum length of the chamber. No go is the larger measurement while field is the amount where a chamberi s not safe to fire. I've made some AR barrels and chambered them to close on a go gauge but not on a no go. This tells me the length of the chamber is the minimum amount. I've bought some commercial barrels where the bolt would close on a no go but not on a field gauge. That tells me the chamber is a little larger and should not have any issues with all ammo, as long as the ammo is made correctly. I believe you should buy a field gauge and see if your bolt closes on that one. If so, do not use it. The length is too large and not safe. Is your barrel new as well as the bolt? I always use a new bolt when chambering a barrel. |
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not trying to high jack or get off topic but...whats the worst that could happen if someone fired a rifle and the chamber was unsafe to fire like that(field gauge test fail)? KABOOM As in case failure, separation, and damage to/destruction of the rifle and/or the SHOOTER. There is a reason for that gauge to be used to reject barrel and bolt combinations. |
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There are three headspace gauges, go, no go, and field. Go gauge measures the minimum length of the chamber. No go is the larger measurement while field is the amount where a chamberi s not safe to fire. I've made some AR barrels and chambered them to close on a go gauge but not on a no go. This tells me the length of the chamber is the minimum amount. I've bought some commercial barrels where the bolt would close on a no go but not on a field gauge. That tells me the chamber is a little larger and should not have any issues with all ammo, as long as the ammo is made correctly. I believe you should buy a field gauge and see if your bolt closes on that one. If so, do not use it. The length is too large and not safe. Is your barrel new as well as the bolt? I always use a new bolt when chambering a barrel. I'm feeling dumb with this. But if I get a Field gauge and it closes on it, don't use it. I got that much. I have an upper and barrel on the way from Rainier Arms and will be using an RRA bolt until Rainier Arms has one back in stock. Hopefully I won't have any problems since I'm using quality parts. Are the gauges from Brownell's the way to go or can I find cheaper ones somewhere? I just placed an order and would hate to pay more shipping. |
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Go and No-Go gauges are not all that useful to a general shooter, practically speaking, and are of almost no value on a used rifle.
The Field gauge is the one you should concern yourself with since this is the safety threshold, as stated in a post above. A chamber that swallows a No-Go gauge is not a safety issue unless that chamber also swallows a Field gauge. |
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Even if the weapon will pass the Colt max chamber gage (1.4736”) now it may not after a few hundred rounds. If this is true, then Colt is negligent in creating the Colt II Field Gauge. Our troop's M16s and M4s are checked with a gauge of that dimension. A "few hundred rounds" could be expended on one mission. |
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Even if the weapon will pass the Colt max chamber gage (1.4736”) now it may not after a few hundred rounds. If this is true, then Colt is negligent in creating the Colt II Field Gauge. Our troop's M16s and M4s are checked with a gauge of that dimension. A "few hundred rounds" could be expended on one mission. You quoted out of context. You are not allowing for breakin with new components. Mil acceptance tests allow up to .0028” increase in headspace in the first 50 rounds I don’t know which field gage is in general issue, but judging from posts I have read the 1.4730” gage is still present. |
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Even if the weapon will pass the Colt max chamber gage (1.4736”) now it may not after a few hundred rounds. If this is true, then Colt is negligent in creating the Colt II Field Gauge. Our troop's M16s and M4s are checked with a gauge of that dimension. A "few hundred rounds" could be expended on one mission. You quoted out of context. I quoted you directly. You are not allowing for breakin with new components.
Mil acceptance tests allow up to .0028” increase in headspace in the first 50 rounds So according to you, a rifle needs to be fired 50 times before a headspace check is even valid ? Where did you get this information ? If this were true it would show up in the Tech Manuals. It does not. I don’t know which field gage is in general issue, but judging from posts I have read the 1.4730” gage is still present.
That's the old Colt gauge. The current gauge is the Colt II (1.4736") |
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You half quoted me and in the process changed the context of what I posted.
As you should well know any given lot of weapons is checked for compliance before being accepted by the government. As this information has nothing to do with maintenance or repair procedures there is no reason for it to be in the TM. AFAIK the only connection between the initial headspace test and the growth test is that in order to know how much headspace has changed they have to know what it was initially. |
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You half quoted me and in the process changed the context of what I posted. As you should well know any given lot of weapons is checked for compliance before being accepted by the government. As this information has nothing to do with maintenance or repair procedures there is no reason for it to be in the TM. AFAIK the only connection between the initial headspace test and the growth test is that in order to know how much headspace has changed they have to know what it was initially. No thanks. I'll stick with what's been working.....standard, approved procedure. |
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You half quoted me and in the process changed the context of what I posted. As you should well know any given lot of weapons is checked for compliance before being accepted by the government. As this information has nothing to do with maintenance or repair procedures there is no reason for it to be in the TM. AFAIK the only connection between the initial headspace test and the growth test is that in order to know how much headspace has changed they have to know what it was initially. No thanks. I'll stick with what's been working.....standard, approved procedure. 
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You half quoted me and in the process changed the context of what I posted. As you should well know any given lot of weapons is checked for compliance before being accepted by the government. As this information has nothing to do with maintenance or repair procedures there is no reason for it to be in the TM. AFAIK the only connection between the initial headspace test and the growth test is that in order to know how much headspace has changed they have to know what it was initially. No thanks. I'll stick with what's been working.....standard, approved procedure. So the counseling didn't work ? 
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From AR15.com :
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" 
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