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Posted: 5/30/2012 6:02:06 AM EDT
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Ok, I have read, read and re-read and am still a little fuzzy on this. The following was taken from the OP for head spacing information:
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" I have built the following with all new mil-spec parts: LMT bolt (bought as complete-built) and Daniel Defense hammer forged barrel. (and DD receiver) 5.56 Now for the questions: It appears that I can use either a accurately spec'd dummy round or a correctly spec'd 5.56 round to check "go". Is this correct? For the "no go" since everything is new and there is zero wear I don't necessarily need a field gage. I can use use the "no go" gage. Is this correct? Brownells has "5.56mm (.223) HEADSPACE GAUGE, Factory Specified Size Measures M16/AR-15 Maximum Headspace" Made to the Colt factory’s special dimensions for M16/AR-15 rifles. Measures the maximum factory acceptable headspace; essential on well-used guns or those that have been rebarreled. SPECS: Hardened and ground steel. 1.65" (4.2cm) overall (this is NOT the “headspace” dimension). .3655" (9.3mm) diameter. Can I use this as my "no go" gage? This is half the price of the Forster below. Same thing? Forster website has the following - HG556NATOMax 5.56 NATO––1.4736" length plus zero minus .0003" (maximum chamber). Or is this the way to go? TIA for all help. |
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Quoted:
Ok, I have read, read and re-read and am still a little fuzzy on this. The following was taken from the OP for head spacing information: 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" I have built the following with all new mil-spec parts: LMT bolt (bought as complete-built) and Daniel Defense hammer forged barrel. (and DD receiver) 5.56 Now for the questions: It appears that I can use either a accurately spec'd dummy round or a correctly spec'd 5.56 round to check "go". Is this correct? For the "no go" since everything is new and there is zero wear I don't necessarily need a field gage. I can use use the "no go" gage. Is this correct? Brownells has "5.56mm (.223) HEADSPACE GAUGE, Factory Specified Size Measures M16/AR-15 Maximum Headspace" Made to the Colt factory’s special dimensions for M16/AR-15 rifles. Measures the maximum factory acceptable headspace; essential on well-used guns or those that have been rebarreled. SPECS: Hardened and ground steel. 1.65" (4.2cm) overall (this is NOT the “headspace” dimension). .3655" (9.3mm) diameter. Can I use this as my "no go" gage? This is half the price of the Forster below. Same thing? Forster website has the following - HG556NATOMax 5.56 NATO––1.4736" length plus zero minus .0003" (maximum chamber). Or is this the way to go? TIA for all help. I use the Colt II Field gauge (1.4736) which is the current military NO-GO gauge. If the bolt closes on this gauge the rifle is considered unsafe to fire. If you need more chamber/bolt info, you'll have to buy a couple of the shorter gauges. Pull the extractor and ejector if you are using a non-rebated rim gauge. Never let the bolt fall on a headspace gauge. |
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This question comes up fairly often.
The proper gauge, and knowing how to use it correctly, is a very good thing to have. The one Direct-Drive mentioned is the correct one, and also the one I have. Here is pretty much a direct copy and paste of a post made by BCM several years ago regarding headspace..... ....A little knowledge is dangerous, but if you must mess around with a headspace gauges get a FIELD gauge.
That is the only one you will need. That is the only one you will need. Not just any field gauge, get the NATO one that Colt recommends........ (.1.4736”).......(Brownells #319-418-033). You are not building barrels, you are not fitting bolts. You are in “the field”, and that is your gauge. Double check the measurements on your gauge. I have seen many gauges with text and not marked with a numeric measurement and even mis-marked dimensions. Get rid of them. Just keep the Colt FIELD Gauge I hope this helps. |
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Quoted:
This question comes up fairly often. The proper gauge, and knowing how to use it correctly, is a very good thing to have. The one Direct-Drive mentioned is the correct one, and also the one I have. Here is pretty much a direct copy and paste of a post made by BCM several years ago regarding headspace..... ....A little knowledge is dangerous, but if you must mess around with a headspace gauges get a FIELD gauge.
That is the only one you will need. That is the only one you will need. Not just any field gauge, get the NATO one that Colt recommends........ (.1.4736”).......(Brownells #319-418-033). You are not building barrels, you are not fitting bolts. You are in “the field”, and that is your gauge. Double check the measurements on your gauge. I have seen many gauges with text and not marked with a numeric measurement and even mis-marked dimensions. Get rid of them. Just keep the Colt FIELD Gauge I hope this helps. I like that. The next time that .223 SAAMI guy shows up I'll C&P that up for him. 
He's back v v v....... 
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Quoted:
With a new bolt and new barrel I expect my headspace to fall between the SAAMI Go and NoGo gages. And, that would be as it it should. But again, for the purpose of "checking" headspace, one doesn't need either a GO nor a NO-GO gauge. Use a Go gage, they are not that expensive. Neither is the recommended FIELD gauge. And again, that's all that is needed to "CHECK" headspace. For me failing the SAAMI Field gage means it is time for a tune up. Good point. And failing the "FIELD" gauge test means the same. GO and NO-GO gauges are used to adjust headspace, the FIELD gauge is used to determine (check) if headspace is within acceptable limits. Since we're dealing with 5.56 NATO, not .223, and we have no practical means of adjusting the headspace, there is no reason to own any gauge other than the one recommended by BCM. That same gauge is also used and recommended by many other reputable builders. We can buy as many gauges we want, including a complete master set in 5.56 NATO, but the FIELD gauge would still be the only one we would need for our purposes. |
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Quoted:
Quoted:
With a new bolt and new barrel I expect my headspace to fall between the SAAMI Go and NoGo gages. And, that would be as it it should. But again, for the purpose of "checking" headspace, one doesn't need either a GO nor a NO-GO gauge. Use a Go gage, they are not that expensive. Neither is the recommended FIELD gauge. And again, that's all that is needed to "CHECK" headspace. For me failing the SAAMI Field gage means it is time for a tune up. Good point. And failing the "FIELD" gauge test means the same. GO and NO-GO gauges are used to adjust headspace, the FIELD gauge is used to determine (check) if headspace is within acceptable limits. Since we're dealing with 5.56 NATO, not .223, and we have no practical means of adjusting the headspace, there is no reason to own any gauge other than the one recommended by BCM. That same gauge is also used and recommended by many other reputable builders. We can buy as many gauges we want, including a complete master set in 5.56 NATO, but the FIELD gauge would still be the only one we would need for our purposes. If that works for you then stick with it. Personally I would like a little warning before hitting the fail point. When I check headspace I want to know what it is within the range of the gages I have. As a reloader SAAMI Field is as far as I want my brass stretched. Also a person can usually adjust headspace some by using a different bolt and with access to right equipment adjustments can be made that would not be cost effective to have done by a shop. |
| Thing is. If is not right there is nothing you can do about it short of a new bolt or barrel. That is a shot in the dark too. Ya don't know if it will fix it or not until you try. It is not like you can by different bolt sizes and know what you need to get your rifle running. It is a binary equation. We are at the mercy of the makers of the parts to do it right. |
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Quoted:
Gentlemen, I appreciate all of your input. I went ahead and ordered stock # 319-418-033WB from Brownells. Thanks for the information it pretty much confirmed what I thought. I love this forum, Most knowledgeable way to learn how to build / work on rifles. Fixed. 
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