AR-15 Head Space

7.62x39Lover

June 11, 2012 17:33

When I am done with the build, I will have to check head space. The Brownell's video has the guy using a "field" guage only. Is there any use for the "go", "no go" guages? I have never checked head space. Any pointers would be much appreciated.

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  Mobuck

  June 11, 2012 18:27

  AR headspace is usually set when the barrel extension is fitted to the barrel. Waiting to"check the headspace?" until you've already assembled the rifle is NOT the best procedure.

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  rufe-snow

  June 11, 2012 20:31

  When I did my build last year, I looked into the headspace aspect. As I recall, it is controlled as the previous poster noted, by the barrel extension where the locking lugs of the bolt engage. If your using a new barrel and bolt, and assemble the barrel assembly to the upper correctly, headspace shouldn't be a problem.
  
  As far as headspace gauges are concerned if you feel the need to use them for a build using new parts,(see the above). There are specific headspace gauge(s) that should be used for a AR build. These are not the same headspace gauges that are used for a bolt action .223/5.56 X 45 caliber rifle. Perhaps this is reason that the guy in Brownell's video was only using a "field" gauge?

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  tsr1965

  June 12, 2012 01:51

  7.62x39,
  
  As above, you can check the headspace, when installing the barrel extension, using the bolt ONLY(no need to use the bolt carrier, as it is not part of the lock up), that you are using. There is no need to wait untill the barrel assembly is installed on the upper.
  
  Best

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  asphalt cowboy

  June 12, 2012 07:11

  As tsr1965 stated, it's much easier to check head-space before installing the barrel to the upper receiver.
  
  As for the "Field" gauge. IMHO Field is , or should be, reserved for battle rifles which Must be returned to battle without proper head-space adjustment being done.
  
  As a 45B I replaced many M16A1 barrels for various reasons and don't recall seeing even one failing the Go/No-Go gauges.
  
  As rufe-snow said, it would be best if you have gauges to match the chamber. 5.56 for 5.56 or .223 for .223
  
  You're going to want a dry chamber to check head-space. Use a patch eye on your rod and a patch or piece or rag large enough to fit the chamber and wipe as much oil out as possible.
  
  Place your barrel in a padded vise in a vertical position and insert a Dry head-space gauge. You don't want oil in the chamber or on the gauge as it can lead to a False reading.
  
  Next insert the Dry bolt into the barrel extension keeping the extractor 90 degrees to the Right of the front sight position and attempt to turn it into a Locked position. Do Not push down on the bolt, just the weight of the bolt itself should be applied to the gauge. With the Go gauge the bolt should turn in with no resistance or just a bare hint of resistance. The bolt should not come anywhere near the locked position with the No-Go gauge.

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  7.62x39Lover

  June 12, 2012 18:14

  Thanks again guys!

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