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Posted: 2/14/2008 7:43:23 PM EDT
| been reading and trying to understand it better. Just bought a used upper and have my own bolt carrier setup I got previously. should I get a gauge to check it? |
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ok, I have only found this one style guage, is this what I need or something more? Where is best place to buy them? I need to put this into barrel or just take bolt out of gun and check? www.brownells.com/aspx/ns/store/ProductDetail.aspx?p=6646&title=5.56mm%20(.223)%20HEADSPACE%20GAUGE |
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On a used set-up, GO and NO-GO gauges won't help you. You'd need to use a FIELD gauge to make sure the gun is safe to fire. GO and NO-GO are more for new set-ups. Chambering a live round will tell you everything a GO gauge will. A NO-GO is a mid-range gauge and will only be helpful if it does not close. If it's a used barrel and bolt combo, which it is, and it swallows a NO-GO gauge, then you still don't know if it's safe or not. FIELD is THE stand-alone safety gauge as it will tell you immediately if the gun's headspace is safe or unsafe. You do not need GO and NO-GO. Something to consider too. .223 and 5.56 have different chamber dimensions, so make sure you know which chamber you have and which chamber the gauge is designed for or you'll get inaccurate results. Thankfully, the inaccuracy will always err on the side of safety. A 5.56 chamber may well swallow a .223 FIELD gauge, but still be quite safe to fire. Just know what you have. |
By that would you mean if got a 223 gauge and it would b e more accurate even used in a 5.56 chamber? Or be best to get the gauge for whatever is on the side of the barrel? |
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this is the one i would need if 223 right? www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=383456 |
If you have a 5.56 barrel, then I would get a 5.56 Field gauge, same with .223. A .223 will work in 5.56, but not the reverse. A .223 chamber is slightly shorter than a 5.56 chamber, so if you use a .223 gauge in a 5.56 chamber, then it will actually go further into the chamber and might indicate a unsafe headspace when in reality the 5.56 headspace is okay. Make sense? If you simply pretend your .223 Field gauge is a 5.56 Field gauge and use it accoirdingly (bolt should not close on a Field gauge), then it will simply mean you have a bit of an added safety margin, though inaccurate. Worst case is that you'll toss out a barrel that actually has a bit more life left in it. Nothing unsafe about that. The gauge you linked will work, but again, if you have a 5.56 barrel I'd get a 5.56 Field gauge just so your readings are clear. |
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Or you could do what I do when goofing around with barrels. Get one of those Hornaday headspace comparators that clamp on to a caliper. Zero the calipers against a known unchambered good factory cartridge, ideally match grade. Strip the bolt of the extractor and firing pin, open the upper and gently close the bolt against the the cartridge. It should close easily. Add laminations of tape to the base of the cartridge and repeat closing the bolt against the cartridge. When you have difficulty closing the bolt or notice resistance, check the cartridge and tape against your zeroed comparitor. You now have a useful headspace dimension you can use instead of a pass/fail that means nothing if you reload everything anyways. |
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Headspace is the distance from the boltface to a datum on the SHOULDER of the non-magnum bottleneck cartridge. It is usually located about halfway down the shoulder. The shoulder is the angled portion of the case just before the neck. The neck is the narrow part where the bullet is seated. Headspace does not, under normal circumstances, change once a chamber is made into the barrel. The onlt way for headspace to change on the AR15, would be to change the bolt, lap the bolt lugs, remove the barrel extension and not index it properly when replacing it, or to replace the barrel extension. The Go/No Go Gages for .223 can be used for the 5.56x45 NATO. They measure headspce, which is, once again, the distance between the bolt face and the datum on the shoulder. The difference between chamber dimensions of the .223 Remington and the 5.56x45 NATO is in the throat, which is not measured by the headspace guage. There is some minor dimensional difference in the chamber length as noted in the link below. The difference in the gages is that the military has greater tolerance range of acceptance for chambers and a slightly longer gage. In other words their tolerances are sloppier than commercial .223 Rem. gages. A Go gage will let you know that the chamber is not too tight and that it will allow the bolt to close on a cartridge that is made to specs. If a Go gage does not "go", then the bolt should not be expected to close on a normal cartridge. A No Go gage will tell you whether or not you have excessive headspace. That means that there is too much distance between the datum on the shounder of the chamber and the bolt face. Too much distance will allow the brass cartridge to stretch to the point of rupture and let out all of that hot expanding gas where it is least desireable. You do not want the bolt to close on the No Go gage. A Field gage stretches the headspace to the undesireable, however safe, absolute maximum distance. So if, in "the field", and the armorer needs to replace a bolt and it goes on the No Go, they will check it with the Fileld gage, and if it does not go on the Field then it is off to the battle field with the absolute sloppiest headspace you can get without blowing up. However, the .223 Field gage is slightly smaller than the 5.56 No Go gage and thus can be adequately used as a 5.56 No Go gage. So, given the accurate information, you can now make the best and safest decision regarding what headspace gage(s) you want to buy. Here is an illustrated depiction of the above: Headspace School Link |
so to sum up what your saying the field gage is the last change to be "safe" whereas if a go / no-go gages are used and it passes those it is definitely good to go, either 223 or 5.56? |
...or not so accurate. A NO-GO gauge DOES NOT indicate unsafe as you state. A bolt closing on a NO-GO gauge requires further investigation before an unsafe head space situation can be determined. The NO-GO gauge should not be swallowed on a new barrel, but again, this is not necessarily indicative of unsafe. There is plenty of barrel/bolt safe life between NO-GO and FIELD. A brand new 5.56 barrel will usually swallow a .223 NO-GO gauge. This isn't because of an unsafe situation but because of the differences in chamber length between 5.56 and .223. |
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I hear and read an awful lot about what is and what isn't "excessive" headspace, and I really have to wonder just how much is hearsay and how much is fact. I read “Hatcher’s Notebook” a number of times, and according to the actual test that he ran, there is an awful lot of smoke being blown by folks that are only going by what they hear from others. The point being that the only “headspace” that really counts is the space between the bolt face and the extractor hook. If the extractor holds the case tight against the bolt face, all you end up with is a longer cartridge case, in effect a wildcat case. If you reload for that rifle and only neck size, you are good to go, but if you have multiple rifles of the same caliber, that’s when you have a problem. If the extractor allows the case to move forward a lot. You can end up with a stretched case, and in really severe cases a ruptured case. A “really severe” case is WAAAAY past any field gauge you have ever seen. You don’t have to believe me, read the book, that chapter starts on page 232. My apologies to those gunsmiths I have offended, but let’s be honest, have you actually seen any of the effects that “excessive headspace” is reported to have, or do you only know about it because of what others have told you? |
The OP asked for an explanation of headspace. Which, since you only addressed the issue of AR15 headspace gages, I provided him with the generally accepted definition of headspace for ALL GUNS using the bottleneck cartridge. A NO GO gage has its dimensions set by SAAMI and since very few chamberings even offer a field gage, it is generally accepted to be used as the final word on chamber safety, as per SAAMI specifications, or perhaps you know better than they do. I do not know any gunsmiths who would let guns out of their shop that go on the No Go. Yes there is some safety factor included in the No Go dimensions, but to send guns that have no Field gage out under those circumstances is a very dangerous and foolish thing to do. If you pass off rifles that go on the No Go that have no Field gage, as safe, then you are fortunate that you haven't yet ended up in court for negligence. So when you get on here and question my accuracy, check youself first. That being said, it is possible to check the actual headspace dimension by taking a few measurements of the bolt and barrel and headspace gages to find out just how out of spec a chamber is and compare those measurements to the SAAMI specs for any given chamber. Then a judgement call must be made whether or not to accept the liability of returning a firearm to a person that is technically out of spec. and may blow up. In addition to the general explanation of headspace, I provided the OP with the information that was specific to the AR 15 5.56 and .223 chambers and provided further specification about the safety of those particular chambers, as well as a link that explained and provided exact dimensions, rather than a vague, use this gage or don't use that gage, as you did. |
A gunsmith must do all he or she can to ensure that safe guns go out of their shop. SAAMI is the Sporting Arms and Ammunition Manufacturers Institute and they have set industry wide standards regarding safe limits of such issues as safe ammunition pressures and chamber dimensions. It is these standars that those in the firearms industry generally refer to as both a legal and physical standard for safety. While it may be true that for Hatcher's testing of the brass available at the time and the guns he used for testing, he was able to go beyond what SAAMI would regard as safe practice, it by no means acceptable for a gunsmith or manufacturer to test SAAMI limits with customers firearms. In short, SAAMI, not gunsmiths, gun writers, or anybody else in this country sets the specs for most headspace applications and those in the industry, follow their guidance for uniformity and safety of standards. |
...as I've been saying from the beginning of the thread. Use a Field gauge. It's the only measurement of value on a used set-up. I don't think you've been reading very carefully or you wouldn't be misrepresenting what I have said nor would you be answering a question so out of context. Remember, we are talking about a used barrel and bolt combo, one that may well test below a NO-GO. Again, doesn't mean unsafe, just used. As long as it passes FIELD, it's safe to fire as far as headspace is concerned. A gunsmith should never allow a new barrel installation out the door that fails NO-GO, not because of safety, but because the customer is being short-changed on barrel longevity. A new barrel that fails NO-GO is one that is born middle-aged and will reach dangerously excessive headspace rather quickly. The customer is losing out on what could amount to many thousands of rounds of use. But, such a barrel is safe to fire provided it passes FIELD. |
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Hey Homeinvader, First off, I apologize for being such an ass in my earlier post. I just got overly sensitive about being challenged for providing inaccurate information. I should have taken it like a man and gone on to prove my point without being an absolute jerk. I'm sorry.  Secondly, I agree with what you are saying. I just wanted to provide more information about headspace, in general, but I guess I did not make that clear. So, I concede that we are in agreement about the use of a field gage. So to the OP: If you want max allowable headspace to still be safe on a .223 chamber AND a 5.56 chamber, then go with the 5.56 Field gage which measures 1.473" of headspace. If you want a tighter tolerance 5.56 chamber or a loose tolerance .223 chamber, then use the .223 Field Gage that measures 1.470". If you want a normal, in spec .223 chamber and an even tighter tolerance 5.56 chamber, use the .223 No Go gage that measures 1.467". Hopefully we are all in agreement on these recommendations. |
I might also add that because of SAMMI, the 7.92 Mauser round which is easily the equal to our 30-06 was neutered to the point of a weak kneed sister. Why. Because they feared that some of the weak minded out there would load the standard .323 dia. bulleted cartridge into an older Gewehr 88 with the smaller bullet diameter. Now tell me that wasn’t due to the fear of being sued because of someone else’s stupidity….. That is just one specific case, there are more, but I’m willing to bet you know that …. |
| I really appreciate all the discussion on headspace in this thread. I now feel well informed on what headspace really is. But on the point of shoulder-to-case head dimension, what about P.O. Ackley's method of blowing the shoulder out and forward to increase case capacity? That, in my mind, would be an unsafe headspace dimension during the fireforming process. I'm not trying to be argumentative here, I just want to make sure I understand everything involved. It seems that headspace only really applies on initial assembly of the barrel-bolt-bolt extension to prevent accidentally ackley-izing our ammunition with full power loads instead of reduced loads. |
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Mercedesman , I see you on your point, and understand in full what you and Hatcher are saying. Your question seemed more directed toward whether everyone just went around regurgitating variations of headspace tales that they have picked up from one place or another, therefore, I addressed that aspect of your prior posting by demonstrating that, no it is not just a bunch of Bubbas sitting around coming up with this stuff but rather an organization whose goal is to ensure a uniform standard so that ammunition from various manufacturers can safely be used in guns from various manufacturers. Yes there is a lot of CYA mentality and justifiably so since almost every trial lawyer in the country would sell their own child to get a piece of a gun company. In regards to the ill affects of SAAMI specs regarding cutting the balls of of some really good cartridges, I agree. One of the most notorious examples is the 45-70 govt. cartridge. It can only be loaded to the highest pressure that the weakest gun chambered for it can handle. So in a modern lever action, this potentially behemoth cartridge, is way under powered. So, either load it up to pressure yourself (outside SAAMI specs), or buy the industry answer, the .450 Marlin ( a slightly different case for the same cartridge loaded to full power). Yes, I agree that excessive headspace, if directed toward the shoulder end, would do nothing more that distort the shoulder, just like blowing the shoulder of a .243 out to a .243 Imp. This is true. EDITED TO ADD: So long as there is not too much unsupporrted case sticking out of the chamber end. On the other hand, I am not going to get on this forum or any other and encourage anyone to do anything but stay within SAAMI specs because all guns are different, and someone may be safe to stretch beyond the limits for their particular application, if they can properly measure their actual headspace deviation, however, this can lead to catastrophinc failure of the gun if imporperly determined. Everything depends on how much and where and at what pressure the stretching takes place. Also without knowing what the actual limits are, one is taking a big gamble. You obviously understand where I am coming from here. And finally, deep breath here, headspace is technically the distance from a datum, to the bolt face. For non-magnum bottlenecks, the datum is somewhere on the shoulder. For collared magnum bottleneck cartridges (such as the .300 Win Mag.) it is the surface that the collar rests on. For rimless straight wall pistol cartridges (such as the .45 ACP), it is the surface that the mouth of the case touches. For rimmed cartridges (such as the .357 Mag.), it is the surface that the rim seats on. You probably already knew all this, but it is the accepted technical definition and a good FYI for those who did not know. Anything we can agree on in there? |
I think pretty much all of it is on the mark.......  My point was, and is, that there is too much myth and hearsay bandied about on headspace on the web. Some people treat it like the Holy Grail when it is only a measurement that can be, and usually is, closer to an arbitrary number then something written in stone. The go, no-go, and field gauges have a place, and should be used as they are designed, but they are not required for every rifle builder on the planet. It seems as though many if not most think that they are required for every upper that they have built whether or not they have assembled the barrel extension to the barrel or not. |
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IVE SEEN IT. i HAVE HAD A NUMBER OF RIFLES, BOLT, LEVER, PUMP, SEMI IN MY SHOP OVER THE YEARS. (damn that caplock) the distance between the extracor hook and bolt face as you say is not the deciding factor on safety. The extractor holding the case? WTF. No way . Use the gauges, You get head seperations gas blow back, incipent head seperations which you cant detect unless you examine the insid eof your brass. Sniperdoc knows of what he speaks. I have been doing bolt guns for 25 years and have threaded, chambered and installed a shitload of barrels. You can get some nasty results with excess headspace. |
I would call them to make sure but I would think that it was done at their shop. On the AR platform, headspace can be checked with the barrel and bolt separated from the gun. It has the locking lugs attached to the barrel with a part called the barrel extension. The bolt locks up on those lugs. The carrier only rotates the bolt and "carries" it back and forth in the upper and therefore is not relevant to headspace. The receiver simply holds the barrel in this situation and is not relevant either. Of course you may already know all this. No insult intended. If it was not done FOR SURE, I would recommend having it done. I personally am not willing to accept the degree of risk associated with not checking it. Odds are that it is fine, but I strongly recommend checking it. BTW it would be easier to do before assembly. Cheers |
Thank you, better safe than sorry. |
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