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Posted: 1/27/2010 8:40:34 PM EDT
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I had Adco put a new Daniel Defense barrel and free float handguard on a Colt HBAR upper I had. Before shooting the gun I decided to check the headspace. I could not close the original Colt bolt on a Forster "GO" gauge. I also tried a number of other bolts that I have (BCM, LMT, other Colts and a Bushmaster) and only the Bushmaster bolt would close on the GO gauge. The Bushmaster bolt has run about 3000 rounds and in its original BM upper it will close on a NO GO gauge so I'm thinking it may be a bit worn. This is the first time I have checked headspace on the BM upper so I don't know what it was like when new.
I believe it should be safe to shoot the Colt/DD upper with the Bushmaster bolt but it seems odd that there is insufficient headspace with all the other bolts, many of them new or close to it. I am wondering if there is a problem with the upper/barrel being out of spec. I emailed Adco and they said not to shoot the upper with a bolt that won't close on the Go gauge. That seems obvious but I am wondering if there is a bigger problem with the upper/barrel. I would appreciate any comments from folks knowledgeable about AR headspace. If the headspace is tight, will the chamber/barrel extension "wear in" so that I could use other bolts after it's been shot a while? Thanks, Bowmanh |
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I am using a .223 gauge. I discussed this with the tech at Brownells when I ordered and he said to use a .223 gauge. He said the actual chamber dimensions are the same between .223 and 5.56 even though the leade is different. The GO/NO GO gauges measure the chamber and not
the leade according to him. Besides, the issue I have is that the DD 5.56 chamber is too tight, not too loose according to the gauge. If the 5.56 gauge were longer I would presumably have even more of a problem. |
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"I would appreciate any comments from folks knowledgeable about AR headspace. If the headspace is tight, will the chamber/barrel extension
"wear in" so that I could use other bolts after it's been shot a while?" Yes. I think your other bigger issue is the barrel starting out tight. Is it chrome lined? If not a turn on a reaming tool will open it up a bit and make it work better with the other bolts. You should contact the barrel maker and see how they address this issue. Please let us know. |
| I did not remove the ejector. I was using the process described by Walt Kuleck and Clint McKee in "The AR-15 Complete Assembly Guide". They do not say anything about removing the ejector. I followed this process with my other AR's and they all close on the GO gauge so the problem is only with this upper. |
Oh my gosh, there is your problem  . Your barrel is more than likely in good shape.
Please remove the ejector when using the headspace gage. Most gages do not have a cut-out to allow for the ejector. (Military gages do.) The ejector will push against the base of your gage and throw off the reading, it takes up space that will throw off your measurement. Make sure you do not allow the gage to be chambered by the rifle spring. Use only finger pressure to push the bolt carrier into the chamber,,,,, Brownells sells a tool to make removal/installation of the bolt ejector & spring easy. http://www.brownells.com/.aspx/pid=18759/Product/AR_15_M16_BOLT_EJECTOR_TOOL Let us know how it works out sir. edited for spelling |
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Quoted:
I can see the logic in what you are saying but if you can't get accurate readings with the ejector in why do all my other bolts close on the GO gauge? Dude, the procedure calls for removing the ejector and the extractor from the bolt. As the other poster stated you should only use finger pressure to close the bolt on the gauge. Do you understand how an AR bolt locks up in the barrel extension? It really isn't the same as a bolt gun. You ask for advice and then argue against. Follow the procedure and only use a stripped bolt. Make sure the chamber, barrel extension, and bolt face are immaculate. I sure hope you haven't been letting the bolt slam home under spring pressure. If so I bet you have a slightly shaved vertical line down the length of your headspace gauge. Here is a less expensive bolt disassembly tool from Brownells. http://www.brownells.com/.aspx/sid=52203/sku/AR_15_M16_Bolt_Vise You don't need the tool to disassemble the bolt but it comes in handy during reassembly. |
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A long answer to why some of your bolts fit and some don't......I am sure someone more knowledgeable can chime in and help.
As I understand the bolt/chamber issues on the AR15 Quality made parts are constructed using a specific process with specific metals, finishing & inspection. That can change slightly from each maker due to their process and tooling. Parts are inspected and tested to meet the specifications within a certain range + or - . When your parts (bolt/chamber) are constructed and held to tight standards, they each have a certain amount of measurement to allow fitting to function. If a bolt measures a bit on the + side, it may still work in a chamber that measures a little on the - side. Too much difference (bolt way + and chamber way -) and you get fitting issues. Brand new and unused bolts/barrels will most times fit and function together if they were well made and inspected. Once you start using a bolt/barrel combination, the parts start to wear together and can reach a point that they can not be swapped amongst other rifles. Several manuals have skull & crossed bones to describe the practice of swapping used bolts with other rifles. Your bolts from Colt, LMT, Bravo Co. etc....all inspected and tested for flaws. Others I don't know,,,,,, A bunch of people will say AR15 rifles do not need headspace checked when throwing them together. I check headspace so I don't blow myself up with an unsafe chamber. In short, if you use parts from well known and quality makers, building rifles goes a lot easier. If you go with unknowns, you get the pleasure of fitting parts and trying to get things to work. |
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I am not arguing. I am just trying to understand what look like conflicting obsevations to me. If removing the ejector is critical, why am I able to get my other guns to close on the Go Gauge? Why is it only with this one? If the problem is the ejector then logic would say that I should have the same problem with all the guns.
BTW, I am doing this with finger pressure only and I was following the procedure in the book mentioned above. I just emailed Adco and according to Steve you don't need to remove the ejector to get an accurate headspace reading. So apparently different folks have different takes on the proper procedure. Just trying to problem solve. I appreciate the comments. |
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The "expert" at Brownells is correct that there is a difference in the "leade" between 5.56&.223rem but there is also a difference between what is acceptable headspace between the bolt face and shoulder of the chamber. There is even a difference between gauges of different manufacturers and chamber reamers of different manufacturers. And there is a difference between .223 & 5.56 headspace gauges.
If you can close the bolt in your chamber with a Forster .223 gauge and then can't pull it back without extreme force your chamber is tight. *edit* this assuming your bolts are in spec and from what you say it sounds like the bolts are all good. |
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I called Daniel Defense and they are sending me a shipping label so that I can send in the upper w/ the Colt bolt. They will look at it and fix any problems. They were extremely helpful and I really appreciate their excellent service and attitude. DD is an excellent company. Why would DD get involved? Great that they will. Good service. But why? Thought you stated ADCO installed the barrel and FFT 458 |
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Quoted:
I am using a .223 gauge. I discussed this with the tech at Brownells when I ordered and he said to use a .223 gauge. He said the actual chamber dimensions are the same between .223 and 5.56 even though the leade is different. The GO/NO GO gauges measure the chamber and not the leade according to him. He is wrong. .223 gauges can show failure in 5.56 chambers. Colts & Bushmasters have 5.56 chambers. The ONLY gauge you need is the military Field gauge. That gauge will show if you have excessive headspace, works in 5.56 chambers, and you don't have to disassemble the bolt like you have to with the civilian gauges. The military Field Headspace Gauge is available from Fulton-Armory. |
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Quoted:
I did not remove the ejector. I was using the process described by Walt Kuleck and Clint McKee in "The AR-15 Complete Assembly Guide". They do not say anything about removing the ejector. I followed this process with my other AR's and they all close on the GO gauge so the problem is only with this upper. The purpose of removing the ejector is that the entire process is very "feel" sensitive. When using the process you mentioned, the ejector is applying forward pressure against the gauge that "Can" affect how the process feels. Even using this process, you should be able to close the bolt using finger pressure, just a little more than normally needed. Some will say that this is too much pressure & that you could damage the chamber. Like any feel test, its subjective. An easy thing to do to make your gauge work properly with the ejector in the bolt (eliminate the varible) is to take a dremel tool with a thin grinding disk and cut out a releif notch large enough for the ejector to freely fit into. Then carefully de-burr the cut. This will eliminate that specific varible. It is very possible that your bolt/bbl combination has a chamber that is slightly short, thus your issue. The fix may be as simple as trying a few different bolts & purchasing the one that works properly. Something to check is how perfectly the bolt fits into the bbl extension without a gauge or cartridge. Remove the bolt from the carrier & just with your fingers insert it and turn it to engauge the locking lugs. It should go right in with no resistance at all and have little or no fore & aft slop. If its tight & the chamber is too, that could be enough to prevent fully closing on a gauge. Then, do a through cleaning of the chamber, bbl extension, bolt face & altered gauge (or don't alter the gauge & remove the ejector from your bolt). Apply a light coat of light oil & test the headspace using just your fingers (i.e, the prefered method). It will do one of several things. 1) goes in - OK. 2) starts closing but doesn't quite completely lock up fully - not enough headspace but barely, you might be able to fix it your self by lapping either the locking lugs or the bolt face as we're talking about less than .001". 3) starts to turn/close but barely, doesn't really come close to closing - headspace is out of spec, try another bolt or send it back to who assembled it. 4) Don't even start to close - chamber is way short and will most likely have to be sent back. And, there is one more test if you haven't done it yet. Take it out & run a few mags out of it & see how it functuns. Most commercial ammo is looser than a GO gauge & a little usage/pounding might be all you need to get it worn into specs (break in). MLG |
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