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bad headspace


HavasuMike

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I thought I was done. I got the barrel a couple days ago and was ready to finish. When I tested the head space, the bolt closed on the NoGo. Today I borrowed my friends bcg and the same thing happened. I emailed Faxon, but have not heard back from them. The barrel is the 20", Heavy Fluted, .308 WIN, Rifle-Length, 416-R Stainless Steel QPQ. The web page says DPMS LR-308. The bcg is Aim Surplus AIM .308/7.62x51 BDG NiB Bolt Carrier Group. Their web page says DPMS pattern. Since this is my first 308 build, I'm totally confused. I am now assuming that I need a different bcg. Any thoughts?

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  • 2 months later...

Sent the barrel and bcg to Faxon. They checked it and said it was good to go. They asked if the go/nogo was a "match" set. The packaging said that it was so I returned them.  Don't know what the difference is between match and not match. Maybe someone that knows about this stuff can explain. Anyway, I finally got it put together and fired a few rounds.  Every thing seemed to work fine. Now I will add a scope to see how it shoots. Thanks to Faxon for their help.  

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  • 4 weeks later...

Gents,

I have a observation regarding HS on AR type barrels. Lets assume you do have a Ar barrel that is out of limits. The only way I see to correct is to adjust the barrel extension with shims. if that were done wouldn't your gas port be out of alignment , meaning it would not be at the 12 o'clock position. I ask because every AR barrel Ive had checked by a PGS has been good to go ......Just my two cents.

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The barrel doesn't rotate, the barrel nut does. Shims to correct a headspace issue would need to be ridiculously thin. No way you could make them durable.

 

Edit...Re-reading this it looks like you mean shimming between the extension and barrel? That would require the barrel to twist I suppose, but I'd guess the same issue would apply.

Edited by blue109
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 Shims wouldn't help , AR Barrels Head Space is determined by the Barrels Chamber & Barrel's Extension Locking Lugs . Barrels Gas Port is the last thing installed after HS has been determined & set.( If installing an A2 ,Tapered Pin Front Sight , that would be the last thing after Gas Port installed ).

 Head space is measured from Bolt face , but Barrel Extension determines that .

Edited by survivalshop
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13 hours ago, survivalshop said:

 Shims wouldn't help , AR Barrels Head Space is determined by the Barrels Chamber & Barrel's Extension Locking Lugs . Barrels Gas Port is the last thing installed after HS has been determined & set.( If installing an A2 ,Tapered Pin Front Sight , that would be the last thing after Gas Port installed ).

 Head space is measured from Bolt face , but Barrel Extension determines that .

I believe you answered my concern , if the head spacing is set/confirmed before the gas port is drilled then every AR type barrel is set, confirmed by QC at the manufacturer. Meaning that when the consumer has HS checked by a LGS hes just doing that for a extra safety check . 

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 For most builders , it would be wise to purchase a Head Spaced Bolt with the Barrel you order or Purchase . I don't trust a some of Barrel makers any more , its the House hold name ones you can believe the Barrels are properly Head Spaced , still good to check . 

 Also some Coatings on some Bolts have seen issues with hindering or causing HS to be off , even though the Barrel Maker's HS is correct from the Factory .

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Our pleasure to help. 

As many have ascertained, it can be difficult to match headspacing on .308 weapon. With no definitive universal spec, we took to publishing what headspace bolt we look for and guarantee headspace with bolts that meet these dimensions:

http://faxonfirearms.com/blog/technical-interface-documents-faxon-barrels/

Hope this helps!

 

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