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Posted: 1/3/2021 9:59:07 AM EDT
[#1]
Something doesn't make sense. I have never heard of Forster gauges being wrong, and the fact you have two is even more suspect that the problem is with something you are doing. Are you reading the measurements from the gauge itself? It's possible you got the wrong gauge or mixed up the packaging?
Describe the process you are using when testing the headspace with the gauge. Have you removed the extractor and ejector from your bolt? |
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Posted: 1/3/2021 10:54:59 AM EDT
[#2]
Yea i removed the extractor and ejector, so just a stripped bolt. The gauges i got have the measurment stamped right on them. One is stamped “Forster 223 Rem Go 5.56 Nato Min 1.4636” and the other is stamped “Forster 5.56 Nato 1.4736 Max”. The method im using is the one were i have just the bolt itself and the barrel and all u do is drop the gauges into the barrel to see if the bolt closes or not on the gauges.
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Posted: 1/3/2021 12:18:08 PM EDT
[#3]
Honestly, I've come across this a couple of times. Put an actual cartridge in it, or if that's not possible a resized case. Everyone I have seen that had an issue closing on a go-gage has closed and functioned fine with an actual cartridge.
YMMV, B |
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Posted: 1/3/2021 12:30:41 PM EDT
[#4]
Thanks, ill try that. Unfortunetly i dont have any 556 yet so looks like ill be hunting some down earlier than i thought. Will definetly update
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Posted: 1/3/2021 12:34:04 PM EDT
[#5]
Get a mic/caliper, mic the gauges.
Did you try rotating the gauges? I would send the gauges back asap, ask them to check them, send new ones. |
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Posted: 1/3/2021 12:53:19 PM EDT
[#6]
Yea i need to mic the gauges. I have a set of mics at work so ill check them when i get there tmrw. I just find it hard to believe i got bad gauges. From what ive read, Forster is pretty decent. I just cant figure out what else could possibly be the issue though. One solid fact from this is that the GO gauge is stamped 1.4636 and the MAX gauge is stamped 1.4736. It doesnt close on the shorter one but closes on the longer one? Makes zero sense
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Posted: 1/3/2021 1:54:15 PM EDT
[#7]
Measuring a headspace gauge, although possible, is not simple. Measurements for most shouldered, rimless rifle chambers are referenced from the datum line, 0.330" for the 5.56 That diameter falls between the shoulder and the neck (tapered part) of the chamber, cartridge or gauge. You can verify (not measure) headspace gauges using a cartridge length gauge used in reloading.
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Posted: 1/3/2021 2:07:26 PM EDT
[#8]
Quote HistoryQuoted: Measuring a headspace gauge, although possible, is not simple. Measurements for most shouldered, rimless rifle chambers are referenced from the datum line, 0.330" for the 5.56 That diameter falls between the shoulder and the neck (tapered part) of the chamber, cartridge or gauge. You can verify (not measure) headspace gauges using a cartridge length gauge used in reloading. mic'ing the gauges for round & dia might reveal something. Since HS is on a datum line that lands on the angled cut, it's almost impossible for diy'er to check that. HS gauges may or may not have same OL, thus the OL # means not much in context of HS. I do prefer one gauge be longer than the other so you can better easily identify which one should be GO vs NO-GO (the OL published by gauge maker). This would at least allow you to check OL to see if perhaps they marked the gauges wrong, etc. What is the OL on this problem set of gauges? Curious to know if they finished the tip to same OL or not, which is an indicator as to how the gauges are cut & finished. And as suitcase mentions, is the bolt side of the gauges nice & flat? My guess is, the gauges were marked wrong. S_it happens. |
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Posted: 1/3/2021 2:10:43 PM EDT
[#9]
Let's assume the gages are correct and start from there. Also, let's assume that the barrel is really chambered for 223/556 NATO.
You said this is a new build so have you cleaned the chamber, the bolt face and the lugs in the barrel extension and the bolt? Have you checked the surfaces above for burrs, metal chips, etc? Are you inserting the bolt into the barrel extension in the same orientation every time and in the same orientation the bolt carrier will present it to the extension? You can try blackening the gage with a Sharpie and seeing where it contacts. There should only be contact at the shoulder area and bolt face. Now, look at the gage and see if it is clean and free of any burrs, chips, etc. Drop it in the chamber and does it center on the shoulder taper and somewhat stick (a taper in a taper should center and sit steady) in position? If it rocks around there is something between the gage and the shoulder taper. Take the gage and fit it to the bolt face. Does it go all the way in to the bolt face or does it catch on the counterbore? It should also sit flat on the bolt face and not rock around but it still may a little as the bolt face may still have some machining marks in it. Hopefully you have found the problem by now. |
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Posted: 1/3/2021 2:40:22 PM EDT
[#10]
Quote HistoryQuoted: Honestly, I've come across this a couple of times. Put an actual cartridge in it, or if that's not possible a resized case. Everyone I have seen that had an issue closing on a go-gage has closed and functioned fine with an actual cartridge. YMMV, B This. |
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Posted: 1/3/2021 5:06:25 PM EDT
[#11]
I don't know what features you intend to measure to try to determine whether the gages were mis-labeled. You probably need an optical comparator, since the relevant dimension is from the base to a point on the shoulder.
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Posted: 1/3/2021 7:01:46 PM EDT
[#12]
True. Yea a micrometer might not actually help determine what the deal is with the gauges since the datum is basically in the middle of the shoulder. I need to get some brass to figure this out i think. Hopefully it’ll just give me a broader picture about what is going on
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Posted: 1/3/2021 7:09:31 PM EDT
[#13]
Quote HistoryQuoted: I don't know what features you intend to measure to try to determine whether the gages were mis-labeled. You probably need an optical comparator, since the relevant dimension is from the base to a point on the shoulder. Dia many times, and OL. A goofy Dia might be culprit. OL might mean mis-labeled if the maker specs a OL for each gauge, etc. Rim flatness could also cause issue. |
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Posted: 1/3/2021 8:03:56 PM EDT
[#14]
A method to check the gauges is to have the BCG out, drop one gauge in the chamber, and using a depth micrometer, and measure from the back of the upper to the back side of the gauge.
Then do the same to the other one. The measurement should be less on the no-go, the go should be a larger distance. If not, the gauges are snafu, send them back. |
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Posted: 1/3/2021 8:45:29 PM EDT
[#15]
Quote HistoryQuoted: Dia many times, and OL. A goofy Dia might be culprit. OL might mean mis-labeled if the maker specs a OL for each gauge, etc. Rim flatness could also cause issue. Quote HistoryQuoted: Quoted: I don't know what features you intend to measure to try to determine whether the gages were mis-labeled. You probably need an optical comparator, since the relevant dimension is from the base to a point on the shoulder. Dia many times, and OL. A goofy Dia might be culprit. OL might mean mis-labeled if the maker specs a OL for each gauge, etc. Rim flatness could also cause issue. When you say "OL" do you mean OAL - which is the reloading term for overall length? If so - there is NO difference in OAL for case gauges. I have the full master set from Forster in 0.001" increments, and they are roughly all the same length. There is no simple way to measure them yourself. The best thing you could do is use a case gauge for reloading, then measure them that way, or use similar headspace gauge reloading tools such as the one from Hornady. |
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Posted: 1/4/2021 10:39:10 AM EDT
[#16]
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Posted: 1/4/2021 10:44:46 AM EDT
[#17]
So not the best picture, but the go gauge shoulder starts higher than the no go gauge. Meaning the base to datum distance is longer on the go gauge making it not close. I dont know, im in the weeds now, this shouldnt be guesswork.
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Posted: 1/4/2021 11:04:19 AM EDT
[#18]
Did you buy these new or used?
From where? Can you show a picture of their markings, the whole gauge, and possibly the packaging they came in? I know you keep using the term "NO GO" but technically that's not correct - the 1.4736 gauge is a FIELD gauge (Colt Field II gauge) and Forster refers to this as a FIELD gauge or a "5.56 NATO MAX". Regardless, there is no way a new barrel and bolt should close on any sort of FIELD gauge. That's defective. But I suspect your gauges right now. At least one of them, and likely your FIELD gauge. |
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Posted: 1/4/2021 11:40:23 AM EDT
[#19]
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Posted: 1/4/2021 12:02:18 PM EDT
[#20]
Bought them brand new from Forster
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Posted: 1/4/2021 12:02:54 PM EDT
[#21]
 Here is your photo hosted properly - I don't think you can link to icloud. Honestly, at this point, I'd call Forster. Can you answer my other questions too? For reference, here is how an older set is marked:  FWIW - there are some being sold on Amazon and Ebay and have horrible reviews of being wrong. I'm wondering if they are counterfeiting these already. That seems odd. But that's what several reviews are saying. I'm guessing you did not buy yours from Brownells or a reputable dealer? https://www.amazon.com/product-reviews/B07TZM3ZN9/ref=acr_dp_hist_1?ie=UTF8&filterByStar=one_star&reviewerType=all_reviews#reviews-filter-bar We have been informed by Forster that there are counterfeit gauges being brought into the country and were originally distributed by third party sellers on Amazon and being resold by other sellers around the internet. Indications of counterfeit Forster gauges are incorrect markings on some gauges and too low prices. Some listings picture actual Forster gauges but counterfeit gauges are sent instead. I think you bought fakes. |
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Posted: 1/4/2021 12:35:33 PM EDT
[#22]
Wow! Thanks so much for help with all this! Yea i actually did buy them from amazon
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Posted: 1/4/2021 1:33:22 PM EDT
[#23]
There are a LOT of items I will not buy on Amazon. The problem is how any seller can introduce counterfeit products into their supply, so it doesn't even matter who you purchase them from. Ships and sold from Amazon contains a LOT of counterfeit products.
Auto parts are one - I never purchase those on Amazon anymore, unless I know its something that isn't counterfeit. It's amazing that gauges are sold enough to be bothered with - it just shows how they will counterfeit anything. Here is another possible giveaway. These gauges are final ground finished to size - not machined. Yours are machined:  |
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Posted: 1/4/2021 2:05:11 PM EDT
[#24]
Quote HistoryQuoted: A method to check the gauges is to have the BCG out, drop one gauge in the chamber, and using a depth micrometer, and measure from the back of the upper to the back side of the gauge. Then do the same to the other one. The measurement should be less on the no-go, the go should be a larger distance. If not, the gauges are snafu, send them back. Excellent suggestion. |
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Posted: 1/4/2021 2:18:02 PM EDT
[#25]
Wow, I really dont know what to say. This is some great research. I never would have thought this was even a thing. Thanks so much for taking the time! Guess Ill think twice when buying parts and tools from Scamazon or any other non firearm website. Ill try Brownells for some legit gauges before I carry on. I appreciate all these suggestions but being this is my first build i just want to do it by the book on this first go with proper gauges. I will update as soon as I get a new set. Thanks!
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Posted: 1/5/2021 12:06:25 AM EDT
[#26]
Quote HistoryQuoted: When you say "OL" do you mean OAL - which is the reloading term for overall length? If so - there is NO difference in OAL for case gauges. I have the full master set from Forster in 0.001" increments, and they are roughly all the same length. There is no simple way to measure them yourself. The best thing you could do is use a case gauge for reloading, then measure them that way, or use similar headspace gauge reloading tools such as the one from Hornady. Yeah, OAL. I add this exaggerated pic for clarity. If they cut OAL with obvious diff, you can then ID which is supposed to be which (eg; GO is the shorter gauge per maker), this would then be a check for mix-up markings, etc. 
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Posted: 1/5/2021 7:18:19 AM EDT
[#27]
I put calipers on them just to get an idea and they were roughly the same OAL. About +/- .0001 of each other. Although like i said the go gauge shoulder started visibly higher meaning the datum would be a longer distance to the base giving it the longer heaspace measurement. At least this is how my brain is processing this. I went and ordered a ptg go gauge right off the phone from ptg should be here by end of the week. It was a 5 week lead time for a no go and a field gauge unfortunetly.
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Posted: 1/5/2021 11:33:23 AM EDT
[#28]
It was a 5 week lead time for a no go and a field gauge unfortunetly. Two pieces of Scotch tape on the back of your go will serve as no-go. |
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Posted: 1/5/2021 11:59:36 AM EDT
[#29]
Quote HistoryQuoted: Two pieces of Scotch tape on the back of your go will serve as no-go. Tape can vary. Layers of tape can vary. And then you are stacking on the tolerances of another gauge. Not my choice for checking HS. Is 4.5thou the right # ?? My 3M Scotch (the wide translucent stuff) is 2.25thou. ~4-5 thou does seem reasonable, but this # is a datum #, not a # to be stacked. Why? Because the GO could be on the low side of the tolerance. see http://ar15barrels.com/data/headspace.pdf SAMMI spec is 10thou(max) on no-go (in gauge cut) ? This is a decent read, see https://eabco.com/Reports/Head_Space_Gauges.htm |
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Posted: 1/5/2021 12:40:30 PM EDT
[#30]
Quote HistoryQuoted: Tape can vary. Layers of tape can vary. And then you are stacking on the tolerances of another gauge. Not my choice for checking HS. Is 4.5thou the right # ?? My 3M Scotch (the wide translucent stuff) is 2.25thou. ~4-5 thou does seem reasonable, but this # is a datum #, not a # to be stacked. Why? Because the GO could be on the low side of the tolerance. see http://ar15barrels.com/data/headspace.pdf SAMMI spec is 10thou(max) on no-go (in gauge cut) ? This is a decent read, see https://eabco.com/Reports/Head_Space_Gauges.htm No-go is really a non-issue anyway, but 2 pieces of Scotch tape will serve the purpose. You can even put it on the back of a FL sized case and forego gauges entirely. If it chambers and fires, you have go. Sooo much over-thinking here. |
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Posted: 1/5/2021 1:53:10 PM EDT
[#31]
Quote HistoryQuoted: No-go is really a non-issue anyway, but 2 pieces of Scotch tape will serve the purpose. You can even put it on the back of a FL sized case and forego gauges entirely. If it chambers and fires, you have go. Sooo much over-thinking here. Wouldn't the "no-go" or field gauge be the one that is desirable for the exact reason you just stated? You could use a empty casing or dummy round as a go. The nogo or field gauges are the ones out spec to say something is wrong and potentially dangerous. I don't know a lot about headspacing but I've always understood that the nogo/field is the one to pay attention too. |
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Posted: 1/5/2021 2:03:32 PM EDT
[#32]
Quote HistoryQuoted: Wouldn't the "no-go" or field gauge be the one that is desirable for the exact reason you just stated? You could use a empty casing or dummy round as a go. The nogo or field gauges are the ones out spec to say something is wrong and potentially dangerous. I don't know a lot about headspacing but I've always understood that the nogo/field is the one to pay attention too. Quote HistoryQuoted: Quoted: No-go is really a non-issue anyway, but 2 pieces of Scotch tape will serve the purpose. You can even put it on the back of a FL sized case and forego gauges entirely. If it chambers and fires, you have go. Sooo much over-thinking here. Wouldn't the "no-go" or field gauge be the one that is desirable for the exact reason you just stated? You could use a empty casing or dummy round as a go. The nogo or field gauges are the ones out spec to say something is wrong and potentially dangerous. I don't know a lot about headspacing but I've always understood that the nogo/field is the one to pay attention too. NO-GO does NOT measure safety. NO-GO measures the maximum chamber size that a NEW chamber should be. If a NEW bolt and barrel close on a NO-GO gauge - something is out of spec. However, some 5.56 NATO chambered barrels will still close on a SAAMI NO-GO gauge.... they are simply being chambered longer than they really need to be. A FIELD gauge measures the maximum chamber dimension considered to be serviceable. It is not necessarily a safety issue, it simply means the chamber size has worn beyond what is considered serviceable and should be replaced. When barrels and bolts are NEW, the chamber dimension should be somewhere between a GO and a NO-GO gauge to be considered within specification. When a chamber can lock on a FIELD, it simply means it is worn beyond its service life, and should be replaced. This is not a "safety" issue really, as the M249 shoots the same ammunition, and will SWALLOW a FIELD gauge when brand new, by design. When your chamber is longer than a FIELD gauge, you do increase the chance of a case head separation, however, because the long chamber allows for the brass to stretch much, much more. The problem with a barrel that will close on a FIELD gauge, is you have no idea how long the chamber is. The reality is, most people should not bother with headspace gauges on an AR-15. It is largely a waste of time, as there is nothing you can really do about it as the headspace is set by the barrel manufacturer. If swapping bolts solves your problem, you never really had one, as you were right on the edge of the GO or NO-GO measurement. Either of which are fine. Buy reputable parts from reputable manufacturers, and go shooting. |
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Posted: 1/5/2021 2:47:23 PM EDT
[#33]
Quote HistoryQuoted: https://i.postimg.cc/JzTgw1Kq/screenshot-374.png Here is your photo hosted properly - I don't think you can link to icloud. Honestly, at this point, I'd call Forster. Can you answer my other questions too? For reference, here is how an older set is marked: https://i.postimg.cc/kMcvYTTN/screenshot-375.png FWIW - there are some being sold on Amazon and Ebay and have horrible reviews of being wrong. I'm wondering if they are counterfeiting these already. That seems odd. But that's what several reviews are saying. I'm guessing you did not buy yours from Brownells or a reputable dealer? https://www.amazon.com/product-reviews/B07TZM3ZN9/ref=acr_dp_hist_1?ie=UTF8&filterByStar=one_star&reviewerType=all_reviews#reviews-filter-bar I think you bought fakes. They may be fakes but I suspect they are correct. Notice in the listing the one marked "NO-GO" has a visibly longer shoulder at the head. His that is visibly longer is marked "GO". So I think they may be correct, just mis-marked. |
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Posted: 1/5/2021 3:08:26 PM EDT
[#34]
Quote HistoryQuoted: They may be fakes but I suspect they are correct. Notice in the listing the one marked "NO-GO" has a visibly longer shoulder at the head. His that is visibly longer is marked "GO". So I think they may be correct, just mis-marked. Quote HistoryQuoted: Quoted: https://i.postimg.cc/JzTgw1Kq/screenshot-374.png Here is your photo hosted properly - I don't think you can link to icloud. Honestly, at this point, I'd call Forster. Can you answer my other questions too? For reference, here is how an older set is marked: https://i.postimg.cc/kMcvYTTN/screenshot-375.png FWIW - there are some being sold on Amazon and Ebay and have horrible reviews of being wrong. I'm wondering if they are counterfeiting these already. That seems odd. But that's what several reviews are saying. I'm guessing you did not buy yours from Brownells or a reputable dealer? https://www.amazon.com/product-reviews/B07TZM3ZN9/ref=acr_dp_hist_1?ie=UTF8&filterByStar=one_star&reviewerType=all_reviews#reviews-filter-bar I think you bought fakes. They may be fakes but I suspect they are correct. Notice in the listing the one marked "NO-GO" has a visibly longer shoulder at the head. His that is visibly longer is marked "GO". So I think they may be correct, just mis-marked. The original gauges are fakes. The photo you are commenting on isn't a real photo - it was edited to make a point, and not a very good one as what he is proposing doesn't exist. And it has NOTHING to do with the actual gauges being discussed here. This is just further evidence that headspace threads are the worst.  |
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Posted: 1/5/2021 3:23:24 PM EDT
[#35]
Quote HistoryQuoted: Wouldn't the "no-go" or field gauge be the one that is desirable for the exact reason you just stated? You could use a empty casing or dummy round as a go. The nogo or field gauges are the ones out spec to say something is wrong and potentially dangerous. I don't know a lot about headspacing but I've always understood that the nogo/field is the one to pay attention too. All a no-go tells you is that the chamber is cut too large. There is nothing "dangerous" about it. The worst that can happen is the brass may split or bulge, possibly making it less than desirable for reloading, or a case head separation in extreme cases which could leave the body in the chamber rendering the gun non-operational. Or, the gun my not fire due to the case seating too deeply for the firing pin to get a good hit on the primer. Also, velocity may drop slightly as the case expands to fill the chamber before the projectile begins travelling down the barrel. Nothing is more over-stated in these forums and over-reacted to, than go/no-go. I can assure you there are a lot of people shooting the shit out of rifles that have chambers that would fail a no-go, but those are also the people who leave their brass on the range floor and don't even bother to look at it. The one thing that will cause a "dangerous" situation is lack of freebore or leade, and gauges will not indicate this. Everybody should take a sharpie and blacken the bullet on a round of ammo and then chamber/eject that round and inspect it. If you see scratches from the lands, or rifling, you indeed have a "potentially dangerous" situation. |
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Posted: 1/5/2021 3:35:07 PM EDT
[#36]
Quote HistoryQuoted:This is not a "safety" issue really, as the M249 shoots the same ammunition, and will SWALLOW a FIELD gauge when brand new, by design. When your chamber is longer than a FIELD gauge, you do increase the chance of a case head separation, however, because the long chamber allows for the brass to stretch much, much more. The problem with a barrel that will close on a FIELD gauge, is you have no idea how long the chamber is. The M249 will not "SWALLOW" a FIELD gauge by design. The build headspace for an M249 is actually shorter than an M16. M16/M4 - - - - - - - - MIN: 1.4646" - - - - - MAX 1.4706" - - - - - FIELD 1.4730" M249* - - - - - - - - - MIN: 1.4611"- - - - - - MAX 1.4649" - - - - - FIELD 1.4688" * The M249 headspace is actually defined as |
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Posted: 1/5/2021 3:43:59 PM EDT
[#37]
Quote HistoryQuoted: The M249 wil not "swallow" a field gauge by design. The build headspace for an M249 is actually shorter than an M16. M16/M4 - - - - - - - - MIN: 1.4646" - - - - - MAX 1.4706" - - - - - FIELD 1.4730" M249* - - - - - - - - - MIN: 1.4611"- - - - - - MAX 1.4649" - - - - - FIELD 1.4688" * The M249 headspace is actually defined as 38.000 +/- 0.08mm and against a 7.663mm (0.3017") reference diameter, I have converted these dimensions to inches against a 0.3300" reference diameter used by the M16/M4 and SAAMI for comparison purposes. Quote HistoryQuoted: Quoted:This is not a "safety" issue really, as the M249 shoots the same ammunition, and will SWALLOW a FIELD gauge when brand new, by design. When your chamber is longer than a FIELD gauge, you do increase the chance of a case head separation, however, because the long chamber allows for the brass to stretch much, much more. The problem with a barrel that will close on a FIELD gauge, is you have no idea how long the chamber is. The M249 wil not "swallow" a field gauge by design. The build headspace for an M249 is actually shorter than an M16. M16/M4 - - - - - - - - MIN: 1.4646" - - - - - MAX 1.4706" - - - - - FIELD 1.4730" M249* - - - - - - - - - MIN: 1.4611"- - - - - - MAX 1.4649" - - - - - FIELD 1.4688" * The M249 headspace is actually defined as 38.000 +/- 0.08mm and against a 7.663mm (0.3017") reference diameter, I have converted these dimensions to inches against a 0.3300" reference diameter used by the M16/M4 and SAAMI for comparison purposes. Cite the source? This data differs completely.... which is what I was basing that off of.  http://www.ar15barrels.com/data/headspace.pdf |
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Posted: 1/5/2021 5:20:49 PM EDT
[#38]
Quote HistoryQuoted: Cite the source? This data differs completely.... which is what I was basing that off of. https://i.postimg.cc/GmDbxP3P/screenshot-378.png http://www.ar15barrels.com/data/headspace.pdf That chart is not correct. He has just converted the metric to inches without taking into account the change in reference diameter. 38.155mm = 1.50216", but this length is against the 7.663mm diameter, not the 0.330 inch diameter used by US designers. Source #1 - DWG 9348200 - Machine Gun, 5.56mm, M249 (19200) (C2):  Source #2 - DWG 9350102 - Gage, Headspace, Reject (19200)  And, a something to show why people mess up when the quote the M249 headspace as longer than an M16 headspace: 
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Posted: 1/5/2021 5:44:28 PM EDT
[#39]
Quote HistoryQuoted: That chart is not correct. He has just converted the metric to inches without taking into account the change in reference diameter. 38.155mm = 1.50216", but this length is against the 7.663mm diameter, not the 0.330 inch diameter used by US designers. Source #1 - DWG 9348200 - Machine Gun, 5.56mm, M249 (19200) (C2): https://i.imgur.com/ICFcB4T.png?1 Source #2 - DWG 9350105 - Gage, Headspace, Reject (19200) https://i.imgur.com/BDfEORN.png And, a something to show why people mess up when the quote the M249 headspace as longer than an M16 headspace: https://i.imgur.com/uRSL4aX.png?1 Quote HistoryQuoted: Quoted: Cite the source? This data differs completely.... which is what I was basing that off of. https://i.postimg.cc/GmDbxP3P/screenshot-378.png http://www.ar15barrels.com/data/headspace.pdf That chart is not correct. He has just converted the metric to inches without taking into account the change in reference diameter. 38.155mm = 1.50216", but this length is against the 7.663mm diameter, not the 0.330 inch diameter used by US designers. Source #1 - DWG 9348200 - Machine Gun, 5.56mm, M249 (19200) (C2): https://i.imgur.com/ICFcB4T.png?1 Source #2 - DWG 9350105 - Gage, Headspace, Reject (19200) https://i.imgur.com/BDfEORN.png And, a something to show why people mess up when the quote the M249 headspace as longer than an M16 headspace: https://i.imgur.com/uRSL4aX.png?1 Thank you! I have searched for that first one and could not find it. |
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Posted: 1/5/2021 5:57:11 PM EDT
[#40]
And, I don't know where he got that 1.4949 - .0002" dimension, the drawing gives 37.96 -.005 mm, or 1.4945 -.0002". Or, converted to US standard: 1.4611"
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Posted: 1/5/2021 6:31:37 PM EDT
[#41]
Oh, and one more thing about that chart, some of the other information is not totally correct either. The specification for an M16 are not the only ones now-a-days, and according to SAAMI's latest information the headspace for .223 Remington is shown below:
M16/M4 - - - - - - - - MIN: 1.4646" - - - - - MAX 1.4706" - - - - - FIELD 1.4730" M249* - - - - - - - - - MIN: 1.4611"- - - - - - MAX 1.4649" - - - - - FIELD 1.4688" H&K 416 (M27)** - - MIN: 1.4646" - - - - - MAX 1.4660" - - - - - FIELD UNK SAAMI- - - - - - MIN: 1.4636"- - - MAX 1.4666"- - - FIELD 1.4736" _ _ _ _ _ _ __ _ _ _ * The M249 headspace is actually defined as 38.000 +/- 0.08mm and against a 7.663mm (0.3017") reference diameter, I have converted these dimensions to inches against a 0.3300" reference diameter used by the M16/M4 and SAAMI for comparison purposes. ** The H&K's headspace in defined in a more complicated German way, and has been converted to US standard for comparison purposes. |
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Posted: 1/5/2021 7:05:49 PM EDT
[#42]
Closing on a no-go can still be ok. It's why you also need a Field gauge. The irony of it all, "closing on a no-go, can still be a go".
Per PTG Pacific Tool and Gauge offers three lengths of headspace gauges per rifle caliber. In order from the shortest to longest, they are: GO, NO-GO, and FIELD: GO: Corresponds to the minimum chamber dimensions. If a rifle closes on a GO gauge, the chamber will accept ammunition that is made to SAAMI’s maximum specifications. The GO gauge is essential for checking a newly-reamed chamber in order to ensure a tight, accurate and safe chamber that will accept SAAMI maximum ammo. Although the GO gauge is necessary for a gunsmith or armorer, it usually has fewer applications for the collector or surplus firearms purchaser. NO-GO: Corresponds to the maximum headspace Forster recommends for gunsmiths chambering new, bolt action rifles. This is NOT a SAAMI-maximum measurement. If a rifle closes on a NO-GO gauge, it may still be within SAAMI specifications or it may have excessive headspace. To determine if there is excessive headspace, the chamber should then be checked with a FIELD gauge. The NO-GO gauge is a valuable tool for checking a newly-reamed chamber in order to ensure a tight and accurate chamber. FIELD: Corresponds to the longest safe headspace. If a rifle closes on a FIELD gauge, its chamber is dangerously close to, or longer than, SAAMI’s specified maximum chamber size. If chamber headspace is excessive, the gun should be taken out of service until it has been inspected and repaired by a competent gunsmith. FIELD gauges are slightly shorter than the SAAMI maximum in order to give a small safety margin. |
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Posted: 1/5/2021 11:14:42 PM EDT
[#43]
Quote HistoryQuoted: Oh, and one more thing about that chart, some of the other information is not totally correct either. The specification for an M16 are not the only ones now-a-days, and according to SAAMI's latest information the headspace for .223 Remington is shown below: M16/M4 - - - - - - - - MIN: 1.4646" - - - - - MAX 1.4706" - - - - - FIELD 1.4730" M249* - - - - - - - - - MIN: 1.4611"- - - - - - MAX 1.4649" - - - - - FIELD 1.4688" H&K 416 (M27)** - - MIN: 1.4646" - - - - - MAX 1.4660" - - - - - FIELD UNK SAAMI- - - - - - MIN: 1.4636"- - - MAX 1.4666"- - - FIELD 1.4736" https://i.postimg.cc/GmDbxP3P/screenshot-378.png _ _ _ _ _ _ __ _ _ _ * The M249 headspace is actually defined as 38.000 +/- 0.08mm and against a 7.663mm (0.3017") reference diameter, I have converted these dimensions to inches against a 0.3300" reference diameter used by the M16/M4 and SAAMI for comparison purposes. ** The H&K's headspace in defined in a more complicated German way, and has been converted to US standard for comparison purposes. The M249 uses a substantial amount of crush-up, does it not? The maximum case length is several thousandths longer than the shortest chamber, to mitigate case stretching due to thermal expansion? |
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Posted: 1/5/2021 11:52:14 PM EDT
[#44]
Quote HistoryQuoted: No-go is really a non-issue anyway, but 2 pieces of Scotch tape will serve the purpose. You can even put it on the back of a FL sized case and forego gauges entirely. If it chambers and fires, you have go. Sooo much over-thinking here. Quote HistoryQuoted: Quoted: Tape can vary. Layers of tape can vary. And then you are stacking on the tolerances of another gauge. Not my choice for checking HS. Is 4.5thou the right # ?? My 3M Scotch (the wide translucent stuff) is 2.25thou. ~4-5 thou does seem reasonable, but this # is a datum #, not a # to be stacked. Why? Because the GO could be on the low side of the tolerance. see http://ar15barrels.com/data/headspace.pdf SAMMI spec is 10thou(max) on no-go (in gauge cut) ? This is a decent read, see https://eabco.com/Reports/Head_Space_Gauges.htm No-go is really a non-issue anyway, but 2 pieces of Scotch tape will serve the purpose. You can even put it on the back of a FL sized case and forego gauges entirely. If it chambers and fires, you have go. Sooo much over-thinking here. You have no way of knowing how long the corresponding headspace dimension on the brass case is, as it is allowed to vary by up to .006" per the government drawing. You have no way of knowing if a case in your possession actually falls within that range, and the OP has no way of knowing if his counterfeight GO-gage actually gages what it says it does - it almost certainly does not. You are under-thinking OP's problem. |
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Posted: 1/6/2021 12:07:42 AM EDT
[#45]
Quote HistoryQuoted: OP has no way of knowing if his counterfeight GO-gage actually gages what it says it does - it almost certainly does not. You are under-thinking OP's problem. So now we need to not only buy and use go and no-go gauges, but we also need to buy a go and no-go gauge checker to make sure the gauges we bought are true? I have more faith in my RCBS sizing die (or a round of ammo from a reputable manufacturer) and some Scotch tape. As I said, if a round will chamber and fire you have your GO. Just shoot it! |
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Posted: 1/6/2021 12:13:52 AM EDT
[#46]
Getting ready to change into someone more comfortable. Name changes coming.
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Posted: 1/6/2021 12:20:07 AM EDT
[#47]
Quote HistoryQuoted: Maybe I am looking at something incorrectly but the Min: 1.4636" looks to be shorter than the max length the case can be? Quote HistoryQuoted: Quoted: Oh, and one more thing about that chart, some of the other information is not totally correct either. The specification for an M16 are not the only ones now-a-days, and according to SAAMI's latest information the headspace for .223 Remington is shown below: M16/M4 - - - - - - - - MIN: 1.4646" - - - - - MAX 1.4706" - - - - - FIELD 1.4730" M249* - - - - - - - - - MIN: 1.4611"- - - - - - MAX 1.4649" - - - - - FIELD 1.4688" H&K 416 (M27)** - - MIN: 1.4646" - - - - - MAX 1.4660" - - - - - FIELD UNK SAAMI- - - - - - MIN: 1.4636"- - - MAX 1.4666"- - - FIELD 1.4736" https://i.postimg.cc/GmDbxP3P/screenshot-378.png _ _ _ _ _ _ __ _ _ _ * The M249 headspace is actually defined as 38.000 +/- 0.08mm and against a 7.663mm (0.3017") reference diameter, I have converted these dimensions to inches against a 0.3300" reference diameter used by the M16/M4 and SAAMI for comparison purposes. ** The H&K's headspace in defined in a more complicated German way, and has been converted to US standard for comparison purposes. Maybe I am looking at something incorrectly but the Min: 1.4636" looks to be shorter than the max length the case can be? It is. A lot of machine guns and rapid-fire weapons use "crush-up", meaning the longest case can be compressed in the shortest chamber. The M240's crush-up is like .010" - quite a lot. It is to mitigate case stretch as the chamber grows due to thermal expansion, or in the case of the M240, due a spongy breach that deflects during firing. |
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Posted: 1/6/2021 6:01:14 PM EDT
[#48]
For reference, 7.62mm NATO headspaces:
M14 - - - - - - - - - - - MIN: 1.6355" - - - - - MAX 1.6385" - - - - - FIELD 1.6455" FAL - - - - - - - - - - - MIN: 1.6315" - - - - - -MAX 1.6380" - - - - - FIELD 1.6400" T48 - - - - - - - - - - - MIN: 1.6305" - - - - - MAX 1.6340" - - - - - FIELD 1.6455" M60 - - - - - - - - - - -MIN: 1.6265" - - - - - -MAX 1.6315" - - - - - FIELD 1.6455" M240 - - - - - - - - - - MIN: 1.6253" - - - - - MAX 1.6336" - - - - - FIELD 1.6400" M110 - - - - - - - - - - -MIN: 1.6300" - - - - - MAX 1.6340" - - - - - FIELD 1.6400" Test Barrel - - - - - - MIN: 1.6280" - - - - - -MAX 1.6310" Oh, and the M240 only has 0.0027" crush with military spec cases and 0.0037 with commercial spec cases, almost the same as the M249 . . . |
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Posted: 1/6/2021 6:47:34 PM EDT
[#49]
Quote HistoryQuoted: For reference, 7.62mm NATO headspaces: M14 - - - - - - - - - - - MIN: 1.6355" - - - - - MAX 1.6385" - - - - - FIELD 1.6455" FAL - - - - - - - - - - - MIN: 1.6315" - - - - - -MAX 1.6380" - - - - - FIELD 1.6400" T48 - - - - - - - - - - - MIN: 1.6305" - - - - - MAX 1.6340" - - - - - FIELD 1.6455" M60 - - - - - - - - - - -MIN: 1.6265" - - - - - -MAX 1.6315" - - - - - FIELD 1.6455" M240 - - - - - - - - - - MIN: 1.6253" - - - - - MAX 1.6336" - - - - - FIELD 1.6400" M110 - - - - - - - - - - -MIN: 1.6300" - - - - - MAX 1.6340" - - - - - FIELD 1.6400" Test Barrel - - - - - - MIN: 1.6280" - - - - - -MAX 1.6310" Oh, and the M240 only has 0.0027" crush with military spec cases and 0.0037 with commercial spec cases, almost the same as the M249 . . . A 7.62x51 case has a headspace dimension of 1.634-.006 on a .400 reference diameter, does it not? Is there a reference diameter discrepancy between the case and the chamber? |
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Posted: 1/7/2021 3:50:59 PM EDT
[#50]
Quote HistoryQuoted: A 7.62x51 case has a headspace dimension of 1.634-.006 on a .400 reference diameter, does it not? Is there a reference diameter discrepancy between the case and the chamber? All of those are against a .4000" reference diameter. Well, I suppose technically the FAL and the M240 is against a 10.16mm reference diameter, being metric and all . . . . (10.16mm = .4000") The thing with the M249 and the HK is that the Europeans, (C.I.P.) define the chamber/case length off the theoretical point of the cone formed by the shoulder. Now, this is an impossible measurement to gauge, so they are free to pick their own reference diameter that actually lies in the shoulder cone. SAAMI defines the case length against a 0.330" diameter, so everybody uses that diameter over here. |
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