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Posted: 8/18/2016 11:30:30 AM EDT
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Who here has properly checked a bolts head spacing on a new quality build and found that it was off spec? If so, is it the barrel or bolts fault?
In the process of building a RECCE style and plan on using a Young NM complete BCG. I will be getting a high quality precision barrel, but plan to pass on a mil-spec bolt / barrel combo. |
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^^^^ have you done the no/go gauge with the extractor taken out? I once had it fail because I was too lazy to take the extractor out at the time, but once I took it out it worked. This was with a reliability though and it doesn't happen with every bolt.
I've since the beginning of the year I've been custom smithing all my ARs besides the pin/weld and cerakote. I've used several different bolt, carrier, upper, and carriers with no issues with headspace. I guess it comes down to reputable manufacturers. I can definitely vouch for Anderson, LMT, Adam's Arms/VDI, and Sharps. |
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FIELD is the only gauge if it fails where you need to be concerned, and if you reload, not even then really. You can always adjust the cartridge headspace to fit your chamber by adjusting your sizing die to not bump back the shoulder as far.
I've built dozens of rifles, mostly wildcats, and never had a bolt fail except one one 5.56 which failed GO, and while it never caused a problem, another bolt brought it back into spec. The old bolt probably would have passed GO after a few thousand rounds once it got settled in, and in fact was used in another build without issue so it was probably a burr that caused it to fail GO in the first place. |
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Im currently working with a manufacturer on their barrel failing a no-go gauge. Several bolt/carrier combos have failed so im thinking its the barrel. Im thinking the things ive read on these and other forums concerning not needing to check headspace on new AR builds has been poor advice. My barrel has maybe 5 to 6 hundred rounds through it and it fails the no-go gauge, thats half the life of the barrel headspace on an essentially new barrel, I feel i bought an expensive upper with a used barrel.
Would you pay for new tires on your truck and settle for half bald treads. You would never know this if you used a field gauge on a new build. |
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Quoted:
Im currently working with a manufacturer on their barrel failing a no-go gauge. Several bolt/carrier combos have failed so im thinking its the barrel. Im thinking the things ive read on these and other forums concerning not needing to check headspace on new AR builds has been poor advice. My barrel has maybe 5 to 6 hundred rounds through it and it fails the no-go gauge, thats half the life of the barrel headspace on an essentially new barrel, I feel i bought an expensive upper with a used barrel. Would you pay for new tires on your truck and settle for half bald treads. You would never know this if you used a field gauge on a new build. Out of curiosity, did you check headspace BEFORE firing those few hundred rounds? If so, was it in or out of spec? If it was out, why did you start shooting it? I have to assume that you didn't, so what made you decide to check headspace on it after you had successfully fired hundreds of rounds? Failing a no-go, but passing a field gauge is not a failure, it just means that you don't have "match grade" headspace. It isn't the bolt's fault, or the barrels fault, it's tolerance stacking between both. If you want a NO-GO pass and match grade accuracy, you should buy bolt and barrel as a combination with that guarantee, instead of mixing and matching parts. No manufacturer is going to replace a barrel that is within tolerances, unless they sold you the set with a guarantee. Most will lean towards looser fitting tolerance in a semi-auto for reliability, anyway. For the record, throat erosion will affect a barrel LONG before headspace will "wear out" on it. As far as the tire analogy, I have to go back to comparing mix-n-match components versus a matched barrel/bolt set. Buying separate components is like putting tires from different manufacturers on each of your rims and wondering why it pulls a little to the side.  Likewise, checking headspace after a few hundred rounds might be like balancing your tires after you've driven as many miles on them.
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I expect barrel manufacturers to build barrels that will pass a no-go gauge when new. A NO-GO gauge failure says you have excessive headspace not that you dont have a "Match Chamber ".
Did not check headspace. Fell into the comfort zone of many that new parts and a AR dont need headspace checked. At the time of this build i was helping build a few AKs an M1a and M1 Garand,so this AR didnt get much range time. After getting out of years of collecting surplus rifles and pistols and the builds i got interested again in the AR. I decided to replace the no name bolt and carrier i had for a name brand combo and use the old one as a back up. I got playing around with measuring bolt dimensions with a new bolt/carrier i bought and found some measurements that got me curious. I bought a n0-go gauge and I was surprised to find the poor headspace which should take thousands of rounds to achieve. My two other new Ar's - DD MK18 and Centurion barrel build have very good headspace and do not fail the no-go gauge . I tried several bolt /carrier combos on this barrel with the no-go gauge ,with and without using the carrier.Two bolts turned with ease and locked ,two others locked half way.I found my PTG no-go gauge is listed as 1.463 GO to 1.469 NO-GO. Thats .006 difference,thats alot for a new barrel . Quoted:
Out of curiosity, did you check headspace BEFORE firing those few hundred rounds? If so, was it in or out of spec? If it was out, why did you start shooting it? I have to assume that you didn't, so what made you decide to check headspace on it after you had successfully fired hundreds of rounds? Failing a no-go, but passing a field gauge is not a failure, it just means that you don't have "match grade" headspace. It isn't the bolt's fault, or the barrels fault, it's tolerance stacking between both. If you want a NO-GO pass and match grade accuracy, you should buy bolt and barrel as a combination with that guarantee, instead of mixing and matching parts. No manufacturer is going to replace a barrel that is within tolerances, unless they sold you the set with a guarantee. Most will lean towards looser fitting tolerance in a semi-auto for reliability, anyway. For the record, throat erosion will affect a barrel LONG before headspace will "wear out" on it. As far as the tire analogy, I have to go back to comparing mix-n-match components versus a matched barrel/bolt set. Buying separate components is like putting tires from different manufacturers on each of your rims and wondering why it pulls a little to the side. Likewise, checking headspace after a few hundred rounds might be like balancing your tires after you've driven as many miles on them.Quoted:
Quoted:
Im currently working with a manufacturer on their barrel failing a no-go gauge. Several bolt/carrier combos have failed so im thinking its the barrel. Im thinking the things ive read on these and other forums concerning not needing to check headspace on new AR builds has been poor advice. My barrel has maybe 5 to 6 hundred rounds through it and it fails the no-go gauge, thats half the life of the barrel headspace on an essentially new barrel, I feel i bought an expensive upper with a used barrel. Would you pay for new tires on your truck and settle for half bald treads. You would never know this if you used a field gauge on a new build. Out of curiosity, did you check headspace BEFORE firing those few hundred rounds? If so, was it in or out of spec? If it was out, why did you start shooting it? I have to assume that you didn't, so what made you decide to check headspace on it after you had successfully fired hundreds of rounds? Failing a no-go, but passing a field gauge is not a failure, it just means that you don't have "match grade" headspace. It isn't the bolt's fault, or the barrels fault, it's tolerance stacking between both. If you want a NO-GO pass and match grade accuracy, you should buy bolt and barrel as a combination with that guarantee, instead of mixing and matching parts. No manufacturer is going to replace a barrel that is within tolerances, unless they sold you the set with a guarantee. Most will lean towards looser fitting tolerance in a semi-auto for reliability, anyway. For the record, throat erosion will affect a barrel LONG before headspace will "wear out" on it. As far as the tire analogy, I have to go back to comparing mix-n-match components versus a matched barrel/bolt set. Buying separate components is like putting tires from different manufacturers on each of your rims and wondering why it pulls a little to the side. Likewise, checking headspace after a few hundred rounds might be like balancing your tires after you've driven as many miles on them. |
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I think I'll just leave this from Forster's Headspace Gauge product information here.
NO-GO: Corresponds to the maximum headspace recommended for gunsmiths chambering new firearms. This is NOT a SAAMI-maximum measurement. If a rifle closes on a NO-GO gage, 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 gage. The NO-GO gage is essential 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 gage, 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 gages are slightly shorter than the SAAMI maximum in order to give a small safety margin. Note: Not my words, but those of someone who manufactures measurement products and is required for liability reasons to know SAAMI requirements. |
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Quoted:
I think I'll just leave this from Forster's Headspace Gauge product information here. Note: Not my words, but those of someone who manufactures measurement products and is required for liability reasons to know SAAMI requirements. Quoted:
I think I'll just leave this from Forster's Headspace Gauge product information here. NO-GO: Corresponds to the maximum headspace recommended for gunsmiths chambering new firearms. This is NOT a SAAMI-maximum measurement. If a rifle closes on a NO-GO gage, 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 gage. The NO-GO gage is essential 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 gage, 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 gages are slightly shorter than the SAAMI maximum in order to give a small safety margin. Note: Not my words, but those of someone who manufactures measurement products and is required for liability reasons to know SAAMI requirements. This is arfcom, gather up your facts and get the hell out of here. 
Some people should not be allowed to play with tools. 
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