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Posted: 9/10/2019 10:16:20 AM EDT
[#1]
The chances of decent quality parts ending up with an out of spec headspace on an AR15 is incredibly low. I'd wager than 99% of home builders never even check it. I know I never have on new parts.
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Posted: 9/10/2019 10:24:51 AM EDT
[#2]
It’s a good idea to check it, but as posted: quality parts = most likely good.
In the case of what you saw at FN, if the bolts are tp print and the barrel extension is to print and installed on the barrel correctly (which can all be inspected prior), then it good. What can yo do if it out? Nothing: headspace is set by the bolt + extension; if headspace is out there’s nothing most “hobbyists can do except replace parts...and find ones that are to print. More important to me is to start checking for wear several thousand rounds down the road. |
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Posted: 9/10/2019 11:23:06 AM EDT
[#3]
Quoted:
When checking head space, you are supposed to do it with the ejector removed, correct? Recently, I watched M-4s being built at FN America and they were checking head space on fully assembled rifles just prior to sending them to the test range. Complete bolt carrier groups were coming out of a box at random, so no way the bolt and barrel had been checked for head space prior to assembly. Are there head space gauges that are designed to be used with fully assembled bolts? So you check head space and it is out of spec. either tight or loose. What do yo do? Buy random bolts until you get one that puts you in spec? Does not sound like a great option for hobbyist builders... Yes there are gauges to do it assembled but not commercially available anywhere I know of right now. You used to could buy the surplus field gauge made for it but I have not seen any for sale lately. Here is a pic of a min. gauge that was sold for a while.  Attached File |
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Posted: 9/10/2019 1:19:30 PM EDT
[#4]
Quote HistoryQuoted:
It’s a good idea to check it, but as posted: quality parts = most likely good. In the case of what you saw at FN, if the bolts are tp print and the barrel extension is to print and installed on the barrel correctly (which can all be inspected prior), then it good. What can yo do if it out? Nothing: headspace is set by the bolt + extension; if headspace is out there’s nothing most “hobbyists can do except replace parts...and find ones that are to print. More important to me is to start checking for wear several thousand rounds down the road. |
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Posted: 9/11/2019 7:39:01 AM EDT
[#5]
Quote HistoryQuoted:
As you put thousands of rounds through rifle headspace can become a issue? If it is can you give me an example of what parts you had to change. Thanks A conventional (i.e. not enhanced like LMT for example) AR-15 bolt can develop cracks as early as 3-5,000 rounds...after that, it’s on borrowed time; it may go another 10,000 rounds, it might go 100...so you’ll be replacing bolts relatively frequently (along with recoil springs) compared to the barrel (ammunition dependent). |
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Posted: 9/11/2019 11:32:53 AM EDT
[#6]
According to Forster with ejector and extractor removed.
Another manufacturer may have different requirements. It is certainly possible for a manufacturer to have gauges compatible with assembled bolts. Some civilian manufacturers try to keep their headspace tight which can result in Go gauge failures. Someone like FN is going to keep their barrels in a range that will work with any in spec bolt. Since I have several bolts on hand for spares, I just pick a bolt that gets the headspace where I want it. If I cannot match a barrel with a bolt the barrel gets sent back. |
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Posted: 9/11/2019 3:43:10 PM EDT
[#7]
To check for (excessive) wear you use a FIELD gauge, which has the maximum allowable headspace dimensions. Once a gun fails a field gauge test you replace the barrel.
I’m kinda confused but I specifically use Daniel defense & spikes fn’s Chrome lined barrels. When should I start to check head spacing for failure? |
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Posted: 9/12/2019 3:43:57 AM EDT
[#8]
Quote HistoryQuoted:
To check for (excessive) wear you use a FIELD gauge, which has the maximum allowable headspace dimensions. Once a gun fails a field gauge test you replace the barrel. I’m kinda confused but I specifically use Daniel defense & spikes fn’s Chrome lined barrels. When should I start to check head spacing for failure? Upwards of twice that with copper jacketed projectiles. It is also dependent upon your firing schedule: the hotter you get your barrel, the faster it wears. |
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Posted: 9/12/2019 7:25:01 AM EDT
[#9]
Quoted:
When checking head space, you are supposed to do it with the ejector removed, correct? Recently, I watched M-4s being built at FN America and they were checking head space on fully assembled rifles just prior to sending them to the test range. Complete bolt carrier groups were coming out of a box at random, so no way the bolt and barrel had been checked for head space prior to assembly. Are there head space gauges that are designed to be used with fully assembled bolts? So you check head space and it is out of spec. either tight or loose. What do yo do? Buy random bolts until you get one that puts you in spec? Does not sound like a great option for hobbyist builders... You can make relief cuts in the base of your head space gauge to clear the ejector/extractor if you wish to do so. Archived Thread on that |
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Posted: 9/12/2019 9:01:44 PM EDT
[#10]
Quote HistoryQuoted: To check for (excessive) wear you use a FIELD gauge, which has the maximum allowable headspace dimensions. Once a gun fails a field gauge test you replace the barrel. A conventional (i.e. not enhanced like LMT for example) AR-15 bolt can develop cracks as early as 3-5,000 rounds...after that, it’s on borrowed time; it may go another 10,000 rounds, it might go 100...so you’ll be replacing bolts relatively frequently (along with recoil springs) compared to the barrel (ammunition dependent). The Army, even with a steady diet of M855A1, figures the bolt life at 10,000 rounds, in an M4 and 15,000 in an M16. |
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Posted: 9/12/2019 9:30:41 PM EDT
[#11]
Quote HistoryQuoted: You can make relief cuts in the base of your head space gauge to clear the ejector/extractor if you wish to do so. Archived Thread on that |
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Posted: 9/12/2019 10:34:42 PM EDT
[#12]
Quote HistoryQuoted:
5000 is a little short for a bolt's life. The Army, even with a steady diet of M855A1, figures the bolt life at 10,000 rounds, in an M4 and 15,000 in an M16. Quote HistoryQuoted:
Quoted: To check for (excessive) wear you use a FIELD gauge, which has the maximum allowable headspace dimensions. Once a gun fails a field gauge test you replace the barrel. A conventional (i.e. not enhanced like LMT for example) AR-15 bolt can develop cracks as early as 3-5,000 rounds...after that, it’s on borrowed time; it may go another 10,000 rounds, it might go 100...so you’ll be replacing bolts relatively frequently (along with recoil springs) compared to the barrel (ammunition dependent). The Army, even with a steady diet of M855A1, figures the bolt life at 10,000 rounds, in an M4 and 15,000 in an M16. |
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Posted: 9/13/2019 3:17:35 PM EDT
[#13]
Quote HistoryQuoted: Read what I wrote carefully: the Army also found that M4 bolts can develop cracks as early as 3,000 rounds and are subject to failure at any point thereafter...may go 10,000 as you stated; might fail at 3,001. There is a huge difference between, "the average life of a bolt is 10,000 rounds", and "5000 rounds...after that, it’s on borrowed time.." Statistically speaking, less than 1% should fail that early....unless they have been abused. Wups, now we're down to 3000.... |
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Posted: 9/13/2019 9:05:24 PM EDT
[#14]
Quote HistoryQuoted:
It’s Ammo dependent: bi-metallic projectiles will render a barrel useless with respect to accuracy/keyholing as early as 10,000 rounds. Upwards of twice that with copper jacketed projectiles. It is also dependent upon your firing schedule: the hotter you get your barrel, the faster it wears. Quote HistoryQuoted:
Quoted:
To check for (excessive) wear you use a FIELD gauge, which has the maximum allowable headspace dimensions. Once a gun fails a field gauge test you replace the barrel. I’m kinda confused but I specifically use Daniel defense & spikes fn’s Chrome lined barrels. When should I start to check head spacing for failure? Upwards of twice that with copper jacketed projectiles. It is also dependent upon your firing schedule: the hotter you get your barrel, the faster it wears. |
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Posted: 9/14/2019 11:33:10 AM EDT
[#15]
Quote HistoryQuoted:
I did. There is a huge difference between, "the average life of a bolt is 10,000 rounds", and "5000 rounds...after that, it’s on borrowed time.." Statistically speaking, less than 1% should fail that early....unless they have been abused. Wups, now we're down to 3000.... I guess you’d better hope you your bolt isn’t one of the 1%. |
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Posted: 9/14/2019 11:34:15 AM EDT
[#16]
Quote HistoryQuoted:
So when a barrel manufacturer says to expect at least 20,000 rounds plus out of a barrel is not entirely accurate? That is why I’ve been spending more on spikes & DD barrels to get most longevity out of them. I don’t mag dump and I switch rifles after a few mags to cool rifle down. |
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