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Posted: 7/8/2010 12:36:54 PM EDT
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I have the "go" and "no go" gauges ... would it be safe to assume that if I had a new "mil-spec" bolt that was stripped and with it and the gauges I could tell if the head space was good or no good on any barrel. The reason I ask is a friend of mine keeps telling me if the barrel is used then I should be using the used bolt that was in it to check the head spacing of that barrel.
Am I wrong here? ETA .. sorry forgot to mention this is on the AR platform |
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The gages measure whatever parts you put together; the barrel, barrel extension, and bolt. Change one, and the actual headspace dimension is different.
The real question is whether the bolt closes on the Go gage, and doesn't close on the No Go gage. I'm interested in hearing the difference in length of your gages. |
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The bolt has to be stripped. The ejector will jam the gages into the chamber. Close the bolt easy - not that hard, easy, it should almost close itself on the go gage. The bolt will close on your No Go gage with a push; that's no good.
You might find some combination of parts where the No Gage will close, then swap the bolt out and find out it won't close on the No Go gage with that bolt. Especially with used parts. |
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The bolt has to be stripped. The ejector will jam the gages into the chamber. Close the bolt easy - not that hard, easy, it should almost close itself on the go gage. The bolt will close on your No Go gage with a push; that's no good. You might find some combination of parts where the No Gage will close, then swap the bolt out and find out it won't close on the No Go gage with that bolt. Especially with used parts. +1 Totally agree, the bolt really does have to be stripped to do a proper job of it. Checking headspace is very "feel" sensitive & you have to eliminate any varibles. lots of people will tell you it doesn't matter much but it does. MLG |
| I know the bolt has to be stripped before you check and have checked several of my own to get the :feel" part of a new bolt in a new barrel .... the reason I ask is a friend has a used barrel w/2-3k rnds and wanted me to check the head space on it. So I take my new already stripped bolt and gages and go over there and with my "new" stripped bolt the barrel checks out GTG. locks to the go no force required and won't lock to the no go even with a "push". He says "no no no you have to use the bolt that was with the barrel to check head space" ... so I oblige him and strip his bolt .. and it locks up on both gages tight on no go but it locks and he thinks the barrels shot .. I keep telling him to just get a new bolt and shoot it. |
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The barrel on an AR that has only shot 3000 rounds should be solid unless it has been abused with lots of hot loads or the parts are substandard.
The problem you have to answer is whether your pal's bolt is bad. But I would also look at the bolt extension right away, too. Put the bolt from his rifle into one of yours. If the bolt closes on the No Go gage, then maybe all he needs to do is buy a new bolt. But I would go over the barrel extension with a fine tooth comb looking for cracks, galling, or any other damage. You'll have to take the barrel out of the receiver to get a good enough look, and then you can put the old bolt in to see how badly it rattles around. |
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The bolt closing on a no-go does not usually mean it's unsafe to fire, just that it's got unacceptably large headspace for a new barrel. Since it's not a new barrel, that point is already moot.
The actual "dispose of" test is the bolt closing on a field gauge. That would indicate potentially unsafe excessive headspace. |
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Just pointing out for clarity that headspace is not a measurement of the barrel, it is a measurement of the relationship between the bolt, barrel and receiver. I understand that ... ... but to me if your checking head space with a used bolt and it locks up to a "no go" then all that is really telling you is "something" or a combination of "somethings" is worn ... but If your checking it with a new bolt and it locks up to the "no go" then that would tell me that there is definitely an issue with the barrel right? ... or ... if the new bolt locked up to the "go" and not the "no go" then that would say to me the barrel is GTG. Or am I completely wrong here? |
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Just pointing out for clarity that headspace is not a measurement of the barrel, it is a measurement of the relationship between the bolt, barrel and receiver. I understand that ... ... but to me if your checking head space with a used bolt and it locks up to a "no go" then all that is really telling you is "something" or a combination of "somethings" is worn ... but If your checking it with a new bolt and it locks up to the "no go" then that would tell me that there is definitely an issue with the barrel right? ... or ... if the new bolt locked up to the "go" and not the "no go" then that would say to me the barrel is GTG. Or am I completely wrong here? Using a different bolt that was not used when the rifle was chambered will not tell you anything other than if that bolt will work with that barrel or not. It could be that the rifle had a long chamber from the get go. You would have to inspect the parts for wear yourself like described already to see if something is wrong. eta: to answer your question after re-reading the OP, no you cannot just have a stripped bolt to test any barrel on. You need a bolt that you know has headspaced good before hand to make any real assumptions about what is happening/has happened. The tolerances involved here are very small and with multiple parts coming together changing any one of them can change headspace dramatically. I know of guys that have a pile of AR bolts, and they just keep trying one until it headspaces correctly. Many times this is easier that putting the barrel back into a lathe and re-cutting, especially if there is a chrome lined bore. The AR platform is different from many others because it has a barrel extension that the bolt locks up into. Most other guns the bolt locks up into the receiver and the barrel is screwed into the receiver. The AR system is better in a lot of ways, but for fixing headspace issues it isn't. Good luck |
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Simple version:
Bolt must close on "Go" Bolt should not close on "No Go" Bolt must not close on "Reject" Worn/New bolt barrel ect,,,doesn't matter. You are checking the relationship of those specific parts together :) Keep a factory new bolt in your drawer to check against barrels. If the bolt you are checking fails to check against your barrel, use the new bolt and check again. If that fails, you know the barrel is in question, not the bolt. Maybe even have a spare set of headspace gauges that have not bee used a bunch, check again with those as all tools can wear out. 
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Just pointing out for clarity that headspace is not a measurement of the barrel, it is a measurement of the relationship between the bolt, barrel and receiver. I understand that ... ... but to me if your checking head space with a used bolt and it locks up to a "no go" then all that is really telling you is "something" or a combination of "somethings" is worn ... but If your checking it with a new bolt and it locks up to the "no go" then that would tell me that there is definitely an issue with the barrel right? ... or ... if the new bolt locked up to the "go" and not the "no go" then that would say to me the barrel is GTG. Or am I completely wrong here? Using a different bolt that was not used when the rifle was chambered will not tell you anything other than if that bolt will work with that barrel or not. It could be that the rifle had a long chamber from the get go. You would have to inspect the parts for wear yourself like described already to see if something is wrong. eta: to answer your question after re-reading the OP, no you cannot just have a stripped bolt to test any barrel on. You need a bolt that you know has headspaced good before hand to make any real assumptions about what is happening/has happened. The tolerances involved here are very small and with multiple parts coming together changing any one of them can change headspace dramatically. I know of guys that have a pile of AR bolts, and they just keep trying one until it headspaces correctly. Many times this is easier that putting the barrel back into a lathe and re-cutting, especially if there is a chrome lined bore. The AR platform is different from many others because it has a barrel extension that the bolt locks up into. Most other guns the bolt locks up into the receiver and the barrel is screwed into the receiver. The AR system is better in a lot of ways, but for fixing headspace issues it isn't. Good luck Sir, for cutting the bolt on the lathe, you are taking a small amount off of the rear of the bolt lugs to get the boltface further from the chamber extension? Thank you. |
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Just pointing out for clarity that headspace is not a measurement of the barrel, it is a measurement of the relationship between the bolt, barrel and receiver. I understand that ... ... but to me if your checking head space with a used bolt and it locks up to a "no go" then all that is really telling you is "something" or a combination of "somethings" is worn ... but If your checking it with a new bolt and it locks up to the "no go" then that would tell me that there is definitely an issue with the barrel right? ... or ... if the new bolt locked up to the "go" and not the "no go" then that would say to me the barrel is GTG. Or am I completely wrong here? Using a different bolt that was not used when the rifle was chambered will not tell you anything other than if that bolt will work with that barrel or not. It could be that the rifle had a long chamber from the get go. You would have to inspect the parts for wear yourself like described already to see if something is wrong. eta: to answer your question after re-reading the OP, no you cannot just have a stripped bolt to test any barrel on. You need a bolt that you know has headspaced good before hand to make any real assumptions about what is happening/has happened. The tolerances involved here are very small and with multiple parts coming together changing any one of them can change headspace dramatically. I know of guys that have a pile of AR bolts, and they just keep trying one until it headspaces correctly. Many times this is easier that putting the barrel back into a lathe and re-cutting, especially if there is a chrome lined bore. The AR platform is different from many others because it has a barrel extension that the bolt locks up into. Most other guns the bolt locks up into the receiver and the barrel is screwed into the receiver. The AR system is better in a lot of ways, but for fixing headspace issues it isn't. Good luck Sir, for cutting the bolt on the lathe, you are taking a small amount off of the rear of the bolt lugs to get the boltface further from the chamber extension? Thank you. I've never chambered an AR, but when we were doing chambering in school I looked at one and remember thinking it wouldn't be fun. I suppose you could cut of the back of the lugs if you were short on the headspace, I don't know how they are hardened off the top of my head, and if you took too much then your headspace is way off. Wouldn't you want to get the rear of the lugs into as much contact with extension as possible before cutting the chamber anyway? That is how I was taught for other rifles. Get the rear locking lug engagement with the receiver to near 100% I'd have to get my hands on one to see and I don't have my own because of heath issues right now. |
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