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Old July 25, 2012, 01:05 AM   #1
Metal god
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I need help on AR head spacing issue

Hi , can you guys help me ? . I need to know if changing the barrel nut on a AR or torquing it down to a different spec then it originaly came at will change the head spacing ?

I just installed a YHM free float quad rail . Everything seems to have went well and it apears to be working right . Im taking it out on friday to test it . I'd hate for it to blow up in my face . Can you help .

If changing the barrel nut or installing a new free foating hand gaurd does not change the head spacing . Then how do you head space a AR ? Do you need to be a gun smith to do so ?

Thanks, Metal
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Old July 25, 2012, 02:10 AM   #2
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No, head space is set by the barrel extension.
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Old July 25, 2012, 06:43 AM   #3
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No, head space is set by the barrel extension.
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Old July 25, 2012, 08:16 PM   #4
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When changing barrels on M16s for the US army in the 70s, all we used was a "field" gauge to check the headspace. With the field gauge in the chamber, the bolt carrier had to stick out past the end of the uppre reciever. If it did, the rifle "passed" and was returned to service.

If it did not pass, we replaced the bolt and tried again. If two (or three) bolts did not pass, we junked the barrel and started over.

In the AR system, the headspace is essentially "fixed" by the fit of the bolt in the barrel extension. There is no provision for adjustment. Unlike a bolt action (and some semis) the barrel cannot be "turned" and rechambered to get in spec. A short chamber might be able to be reamed into spec. One that is too "long" can only be replaced barrel/bolts until in spec is achieved.

Note: not a current AR builder, so today some different things might be possible. Was an Army Small Arms Repairman (NOT AN ARMORER) in the 70s.

Barrel nut tension has no effect on headspace.
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Old July 26, 2012, 09:39 AM   #5
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If the barrel extension, and the bolt are within specs, you're GTG as stated above.

Setup is no different than quick-change barrel setups on other semi's and even bolt guns.

For me, if I were changing barrels on a bolt that had a lot of rounds on it, it would be a good time to check. Headspace will increase from wear on the lugs on any rifle.

However, I have no idea of what kind of round count would be necessary to cause any appreciable wear of the lugs on an AR bolt, would probably depend on the quality of the bolt, as well. If anyone knows, it would be interesting to find out.

Keep in mind, also- that all parts have a range of acceptable "tolerances"- so if you happen to have a bolt, and a barrel, that are on the "margins", there would be less safety margin.
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Old July 28, 2012, 02:43 AM   #6
Metal god
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I took the gun out to the range today .We were going to some BLM land today but they closed it do to brush fire danger . Its been hot and dry around here so its ok . We ended up going to Southbay rod & gun club .

I did a bunch to the gun in the last two weeks . New grip , stock , free float quad , gas block , bi-pod , red dot and mag well grip . The gun worked great , its a little heavy . I would not want to carry it all day on a hunt ,but going out and just plinking with it was fun . I'll post a photo or two of the before and after as soon as i down load them. It came out good , and it looks mean .

Thanks for helping me understand the headspacing issue .




Last edited by Metal god; July 31, 2012 at 07:12 PM.
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