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Posted: 7/8/2009 12:28:54 PM EDT
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First, I've searched and read the forum on headspace topics.
Now - I have a surplus 5.56 M16A1 20" upper & have a new BCM bcg to go with it. I don't have HS gauges so I stopped by a local gunsmith today and asked him to check the headspace ($10 what the heck). He used .223 gauges - closed on the GO - THEN - closed on the NO-GO  . He seemed to think it would be ok with a field gauge - but he didn't have one. The whole thing makes me wonder, as he checked it with the ejector and extractor installed  . Came home, mated it to a lower - it will chamber a live M193 round no problem.
Question is: what would you do? Buy a field gauge and check it? Or other input? |
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The headspace dimension is the same for both 223 Rem and 5.56.
The difference between GO and NOGO is 0.003" The difference between GO and FIELD REJECT is 0.006" If the bolt closed snugly on the NOGO, then you're OK. This just means that the chamber is near the max dimension. Yes, it is a bit more difficult to make this determination with the ejector and extractor in place. As I understand it, NATO chambers are intentionally near the max dimension to decrease dirt/crud/crap related malfunctions. |
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Quoted:
Thanks for your input. He said although it closed on the No-Go - he felt friction, it wasn't as if it swallowed up the gauge. That means it is at the NOGO dimension, not beyond. This is not a problem for the AR. If you require maximum accuracy from the rifle, and you can get excellent accuracy from the AR, you may want to go with a custom barrel and a chamber size closer to the minimum GO dimension. This also helps improve case life; an important consideration for match-prepped brass. If you are not expecting better than MOA accuracy, your chamber is just fine. An MOA rifle is certainly a keeper for all but the pickiest shooters. |
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Quoted:
I'm betting that the Field Ga. won't even close. It's obvious when that happens. You should be good to go. Barrels are inexpensive if you need one someday down the road. SpecOps-13, you would have won the bet! Got the field headspace gauge in today (by the way - as advertised: New USGI in wrapper). Popped her in - bolt would NOT close! I am good-to-go!!! |
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I'm betting that the Field Ga. won't even close. It's obvious when that happens. You should be good to go. Barrels are inexpensive if you need one someday down the road. SpecOps-13, you would have won the bet! Got the field headspace gauge in today (by the way - as advertised: New USGI in wrapper). Popped her in - bolt would NOT close! I am good-to-go!!! Also, a field gauge should have a releif cut and should be able to be used with the ejector/extractor in place. |
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I'm betting that the Field Ga. won't even close. It's obvious when that happens. You should be good to go. Barrels are inexpensive if you need one someday down the road. SpecOps-13, you would have won the bet! Got the field headspace gauge in today (by the way - as advertised: New USGI in wrapper). Popped her in - bolt would NOT close! I am good-to-go!!! Also, a field gauge should have a releif cut and should be able to be used with the ejector/extractor in place. Exactly - the field gauge I got from Bill Ricca is used with the ejector and extractor in place. $35 bucks well spent. |
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Quoted:
First, I've searched and read the forum on headspace topics. Now - I have a surplus 5.56 M16A1 20" upper & have a new BCM bcg to go with it. I don't have HS gauges so I stopped by a local gunsmith today and asked him to check the headspace ($10 what the heck). He used .223 gauges - closed on the GO - THEN - closed on the NO-GO . He seemed to think it would be ok with a field gauge - but he didn't have one. The whole thing makes me wonder, as he checked it with the ejector and extractor installed . Came home, mated it to a lower - it will chamber a live M193 round no problem.
Question is: what would you do? Buy a field gauge and check it? Or other input? Check out http://www.brownells.com/.aspx/pid=6646/Product/5_56mm___223__HEADSPACE_GAUGE http://www.brownells.com/.aspx/pid=19183/Product/FORSTER_HEADSPACE_GAUGES http://www.brownells.com/.aspx/sid=15878/pid=19183/sku/NO_GO___223_Rem http://www.brownells.com/.aspx/sid=15881/pid=19183/sku/Field___223_Rem http://www.brownells.com/.aspx/sid=51827/pid=27266/sku/NO_GO__5_56_NATO http://www.midwayusa.com/Search/Default.aspx#headspace%205.56____-_1-2-4_8-16-32 God bless Wyr |
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For those interested (I have no connection with).
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 Scroll down, you'll find it. My experience, he was a good guy to deal with. |
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