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Posted: 4/1/2011 1:31:51 PM EDT
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A while back, someone posted excellent step-by-step instructions for using
headspace gauges and measuring headspace. I could not find this post through searching. Can anyone point me in the right direction? |
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Strip your bolt of the extractor and ejector. You do not want them to influence the reading. Insert the gauges and close the bolt using finger pressure only. Don't let the bolt slam into battery, the gauge can be damaged. Go- Gauge allows bolt to close=Good. Gauge stops short of allowing bolt to close=Bad (short headspace, try a used bolt) No Go - Gauge allows bolt to almost close=Good. Gauge allows bolt to close=Bad (Headspace getting long but will still work for a while, as long as not Field Reject) Field - Gauge prevents bolt from closing=Good. Gauge allows bolt to close=Bad (Headspace long, time for new bolt or maybe barrel, should not shoot further) If you get a reading that is bad, try another bolt. New parts all around should be good, and if they are not good, they need to be returned for good parts. Buy quality parts unless you can make them fit 
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I guess I should have been more specific.
My friend has an upper from an unknown manufacturer. He has only shot .223 ammo through it. I told him to check headspace before running 5.56 ammo. I think that if chambered for .556, the bolt should close on a .223 no-go gauge. Is this wrong? Should the bolt "almost" close, but not quit on a .223 "no-go"? |
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In that case: If the bolt/barrel combination has been working well and passes headspace issues using .223 gauges............. Just check the combination using a military 5.56 Field Reject gauge. They may be hard to locate but have been available from several sources. The 5.56 case would be a problem if you had a tight chamber, passes Go but barely closes on No-Go. If it almost closes on a No-Go, you may have a 5.56 chambering. Only way to know for sure is to have your gunsmith check the chamber, possibly make a chamber casting with Cerosafe and good measuring. The "hold my beer" method of checking would to be- shoot some 5.56 and look for high pressure signs on the brass, hard extraction, etc.  http://ar15barrels.com/data/headspace.pdf EDIT: Here you go : M16 Maximum Headspace Gage, Ordnance Part Number 7799734, NSN 4933-00-070-7814. Disassembly of bolt not needed, gage is cut for extractor and ejector clearance. Each gage is new, in US GI pack. $35.00 PHOTO http://www.billricca.com/collectors_corner.htm |
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