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Posted: 6/19/2014 7:14:17 PM EDT
| I've heard that to check the headspace I need to remove the extractor claw and ejector pin from the bolt. When done, I should insert the Go gauge into the chamber and then insert the bolt and see if I can turn it. If yes, it's a Go. Repeat process with the No Go gauge and if I can turn it it's a No Go. If I can't turn it, it's a Go. All this is done without even attaching the barrel, which makes sense to me. What I don't understand is why I need to remove the ejector pin. I performed the above tasks without removing the ejector pin and completed both tests for a Go--I could turn the bolt with the Go gauge in and could not turn the bolt with the No Go gauge in. The question is, then, why should I remove the ejector pin when it appears I can complete both tests without doing so? What am I not seeing? TIA |
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The ejector pushes against the back of the gauge and can cause a faulty result.
Military gauge sets have a relief cut so the removal of the ejector is no longer required. Saves time when you don't have to punch out the roll pin and remove the spring and plunger everytime. Think of the ejector pushing the gauge unevenly and you can see why its a good idea to get it out of play. |
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I'm building an upper in 5.45x39 and I have run into something that has me scratching my head. The barrel and bolt were purchased from the same vendor. Being thorough I checked the headspace with go/no-go gauges from Brownells. They both allow the bolt to go into battery (lock) without resistance. That is great for the go gauge but I thought that was an issue for the no-go gauge. I took the bolt from my M&P 15 in 5.45x39, disassembled it and had the same problem. I headspaced the new bolt in my M&P15 and the go gauge went and the no-go gauge did not. I sent the barrel back and they sent me a replacement. I checked the replacement barrel and I got the same results as I did with the first one they sent me. I read somewhere on here that some Mil-spec barrels will headspace where the go AND no-go gauge will both allow the bolt to go into battery. Now I am confused. everything I read says headspace is important and bad things happen if it's not right now I read that on an AR it may be okay if the no-go locks into battery. Can someone please explain this to me?
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| A Go and No Go give you limits on each end of the headspace specs. If the bolt won't close on a Go gauge, chamber is too short. Some folks just use a Go and Field. If it closes on the Go and not the Field, you're GTG. When fitting threaded bbls., I would adjust headspace so the bolt just closed on a Go gauge. When fitting the bbl. extension on an AR bbl., they might allow for a tad looser tolerance just due to the manner in which bbls. are interchanged. On a bolt rifle, you can be a little more picky as the bbl. is usually on there for the long haul. |
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Quoted:
so, for normal folks that are only checking headspace, wouldn't a cartridge be a suitable Go-Gauge? Yes. But for safety sake, I use a .223 snap cap as a Go gauge. I'm not going to put a live round in a chamber and have it pointing at things that I don't want to destroy, as miniscule as the possibility might be. |
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Go and No-go gages are for new bolts and barrels.
If you fail the No-go gage the weapon may be safe to shoot, but may also fail a field/max chamber gage before the barrel would be considered shot out. 223 REM and 5.56mm have different specifications for Go, No-go, and field. If you look at the SAAMI chamber drawing they have set the max chamber to 1.4736”, but a 223 REM Field gage is actually close to the US mil-spec No-go. A person can use 223 REM gages to check a 5.56mm chamber, but he must go by the measurement marked on the gage not the nomenclature. Example: My last DD 5.56mm chamber closed on a 1.4646” gage and did not close on a 1.4656” gage; so this weapon will pass either 223 REM specs or US mil-spec. If instead it had closed on a 1.4666” (223 REM No-go spec) gage and not closed on a1.4676” gage it would not pass 223 REM No-go specs, but would pass US mil-spec No-go. Using a case for a gage can be very misleading. The tolerance for cases is several thousandths the tolerance for the gages in the tenths of thousandths. Go to the SAAMI web site and look at the 223 REM chamber/cartridge drawing. |
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There is a nice chart floating around in the archives somwhere showing the dimensional differences between the .223 and 5.56 headspace gauges, along with the dimensional ranges of .223, .223 Wylde, 5.56 and M249 barrels. The headspaces get a little larger as you go from .223 --> M249, with M249 chamber being very generous with the headspace.
Basically, I don't worry unless it closes on a .223 Field gauge, and even then if it's a M249 barrel, I probably wouldn't worry much if it seems like it's barely closing. I don't remove the ejector either. Only the extractor, and do the check with the bbl installed and BCG assembled without ejector. Because believe it or not, I'm at the conclusion that the barrel install can slightly effect headspeace by tweaking the barrel extention a little as the receiver deforms a little from the torque. High torque or galling from lack of grease can make the receiver / extension deformation worse. The deformation is slight so it's within the elastic zone of the metal, therefore the receiver and extension return back to original shape when disassembled and the torque relieved (in case you ever need to fix one that's been tweaked). That's why use of grease is important on the barrel nut and receiver threads. It reduces the galling and torsional force imparted onto the receiver threads from tightening the nut. |
| Loaded rounds (and snap caps) are NOT suitable substitutes for GO gages. The GO gage measures minimum chamber headspace. Loaded rounds are made somewhere between minimum and maximum cartridge headspace dimensions. They are NOT equivalent. Any random loaded round (or snap cap, or dummy round) will be sized to chamber easily, and may easily chamber in a sub-minimum headspaced chamber. Spend the $30 and get a real headspace gage, or find a buddy who has one. Really. |
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IMO GHPorter got it exactly right.
A weapon can be short chambered and a person would never know until he loads up some ammo that is max tolerance. Ever wonder why only some weapons KB with bad ammo instead of every weapon the bad ammo is fired in? I have never run across a 5.56 NATO barrel that failed the 1.4706” No-go gage. On the other hand I have run across several barrels that failed a 1.4636” Go gage. Keep in mind the US mil-spec is 1.4646” for Go. Most of the time this can be fixed by using a bolt that is on the loose side of the tolerance range for bolts. |
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okay, so use a go, then no-go, and if no-go fails-use a field?
if go or field fail, then you have an unsafe headspace? and, you must remove extractor for proper measurement? and lastly, where do I get them? Fulton Armory has a set for the cheapest I've seen, but they look like they're marked 223. I intend to be able to utilize both .223 and 5.56 in my 5.56 chamber. |
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Quoted:
okay, so use a go, then no-go, and if no-go fails-use a field? if go or field fail, then you have an unsafe headspace? and, you must remove extractor for proper measurement? and lastly, where do I get them? Fulton Armory has a set for the cheapest I've seen, but they look like they're marked 223. I intend to be able to utilize both .223 and 5.56 in my 5.56 chamber. If your bolt does not close on a GO gauge, your chamber is smaller than minimum and is not safe. If your bolt closes on a NO-GO gauge, your chamber is past maximum and is unsafe. A FIELD gauge is supposed to be used on military rifles "in the field," and if that fails, your chamber is grossly unsafe. With a GO gauge, remove the extractor AND ejector for the best sensitivity in testing. You can leave the ejector in and give it a try, but if you have ANY doubt whether or not the bolt closed with LIGHT finger pressure, take out the ejector and try again. With a NO GO or FIELD gauge, always remove the extractor. If you can't tell whether the resistance you feel is because the bolt doesn't want to lock or because of the ejector, pull the ejector and try again. For me, it's easier just to remove both extractor and ejector before this test. I have both gauges, and I do first the GO, then the NO GO gauge. Never had one fail, and since you really don't do this test all that often (I HOPE!), it's not that much of a pain. |
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So, I just ordered some Forster gages for 5.56 NATO chamber. Only they are labeled minimum 1.4636 and maximum 1.4736
This seems to correspond roughly to a civilian Go gage and precisely to a Colt Field 2 gage? Will these be fine, or should I have gotten go-no/go ? |
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Quoted:
So, I just ordered some Forster gages for 5.56 NATO chamber. Only they are labeled minimum 1.4636 and maximum 1.4736 This seems to correspond roughly to a civilian Go gage and precisely to a Colt Field 2 gage? Will these be fine, or should I have gotten go-no/go ? Go ahead and call them "GO" and "NO-GO" (or "FIELD") for your convenience. Any headspace gauge is made to a specific headspace dimension length, and the ones you ordered are, as you noted, roughly equivalent to "civilian" values for GO and Colt's FIELD gauge, so they'll do the job. (I just noticed that I've been switching back and forth between using "gage" and "gauge." A quick visit to the Oxford English Dictionary tells me that they are functionally equivalent... Sorry to be inconsistent with this.) |
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The gages are the same for 223 Rem and 5.56mm.
The difference is in the specifications for Go, No-go, and Field. A 1.4636” gage measures 1.4636” in 223 REM and 5.56mm. The 1.4636” measurement is the SAAMI Go (minimum chamber headspace), however the US mil-spec for Go is 1.4646”. The US mil-spec for No-go is 1.4706”. The US mil-spec also specifies a maximum amount of change in the headspace that is allowed for a specific number of test firing cycles. These two specs insure military M16/M4 weapons will meet a minimum service life before failing the Field gage. The 223 REM spec for No-go is 1.4666”. Most of the 5.56 NATO barrels I have checked will pass the 223 REM No-go gage, but not all did. The last 223 REM Field gage I bought measures 1.4696”, which is very close to the US mil-spec 1.4706” No-go gage. I have not personally checked a new 5.56 NATO barrel that failed the 1.4696” 223 REM Field gage. IMO for a new unfired weapon the 223 REM spec three gage set will work for a 5.56 NATO chambered barrel. However for the long run a person would want to add a 1.4736” gage as this is currently considered the maximum safe headspace. There is also an additional complication to the headspace issue. The headspace is measured from the bolt face to a datum line in the chamber. Bolts also have manufacturing tolerances. My experience is different bolts with a given barrel can cause up to a couple of thousandths change in headspace. |
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