First build, and already planning another one, but that's what happens when the wife DVR's a sniper thing on the military channel and gets all excited.  Anyway, I have ordered a set of .223 Go No-Go Gauges from Midway.  Then I read that without 'true' 5.56 gauges I could still be in trouble and that I need the exact 5.56 gauges.

I get it that the neck areas of them are supposed to be slightly different.  Therefore the barrel (still not acquired if you have an extra to sell) is slightly different.  Therefore, I need a 'real' 5.56 chambering in that regard.  It is my understanding though that the cases head space off the shoulder.  Or, am I missing something here?

Now I've been a reloader from way back, and since there is no external difference in the dimensions of the 2 cases I don't see an issue, but since this is my first build I was hoping for some guidance from some more experienced builders out there.

Thanks
Dan

It is my understanding that both cartridge cases have identical outside dimensions.  I know a 5.56 chamber has a longer throat, but does that affect head-space?  I'm thinking not.  I was under the impression that both carts head-space off the datum line.

Either way, what you really need is a Field gauge.  Unless you are cutting the chamber yourself with a chamber reamer, you shouldn't need the go or no-go.  The Field gauge is just for a safety check.

You can use your go and no-go gauges for the safety check, but what happens when the go goes and the no-go goes?  You still don't know if the bolt/barrel combination are safe to shoot.

Remember to strip the bolt of the ejector and extractor before using your gauges.  I would get them (and did), cheap insurance you built it safe.

If the bolt rotates on a no-go gauge then I'm not shooting it.  In that case send the barrel with the bolt back to the barrel manufacturer and tell them to make it right.

I'm still confused.  Can I use the .223, or do I have to buy 5.56 guages?

Dan

If the bolt closes on a no-go, that does not indicate an unsafe condition or that the barrel somehow defective.

I do not know definitively if .223 and 5.56 headspace gauges are completely interchangeable.  I assume that they are based on my current working understanding.  Lord knows I've been wrong before.

Even if the bolt closes on a Field gauge, that does not indicate an issue with the barrel.  It could just as easily be an issue with the bolt.

Check out this thread: http://www.ar15.com/forums/topic.html?b=3&f=118&t=482709

ETA: If you don't want to remove the extractor and ejector, check out the Bill Ricca link in the thread above.

That thread states that there is a difference, but does not describe what the difference is.

What exactly is different between a .223 and a 5.56 field gauge?

The 5.56 field gage allows more wear before rejection.

I don't understand it myself. Forster makes the following claim in their Headspace Gage instruction sheet that comes with their 5.56 gage.



I personally had problems using .223 gages on my 5.56 chambered barrel. So I do believe there is a difference.

Ah, OK.  So the 5.56 Field gauge is ever so slightly longer.  So you CAN use a .223 gauge, the .223 gauge is shorter, there is no safety concern.

I have seen stuff on the net showing a difference in lengths of a 5.56 Go gauge and a 223 Go gauge.

Yea, but the important thing is that it is perfectly safe to use a .223 Field gauge to check for excessive head space on a 5.56 chamber.

I thought about buying the guages and then started checking local gunshops and they would only charge $20 for the check, so I did not buy. I used all new parts and did not get it checked and have had no problems. It's my understanding that if you are using used parts, either old barrel with new bolt or old bolt with new barrel you should have the headspace checked. It is also my understanding that 223 guages cannot be used to headspace the 5.56 chamber and 5.56 guages cannot be used in a 223 chamber.

Thanks for all the input. I found this on the Forster Sight that explains it.  Now I can't decide whether to keep the .223 or exchange/return them.  OOOPS.

http://www.forsterproducts.com/client_images/catalog19938/pages/files/NATO_Headspace_Gage_NHG001-001.pdf

Google and reading is your friend. If I was going to spend my money on gauges, I certainly would want to buy the right tool for the job. If Go gauges are the minimum and Field gauges are the maximum, why would you use a .223 in a 5.56 or a 5.56 in a .223 ? Get them mixed up and your not checking anything right. Doesn't make sense to me. There is just a small amount of difference in the gauges. I don't have a .223 chamber, but I have 5.56 nato, Wylde and Match. The fired brass that comes out of each is different in headspace by only .004". The 5.56 is the longest, then the match and the wylde being the tightest. Just my take on the subject. YMMV.

When I bought my .223 gauges the write-up in the description said they were the same. They at least said .223 could be used in 5.56. They are Forester; the link above seems to be a statement meant to cover some prior miss information.

All that being said, I have checked a dozen rifles with mine. Up until the last one all 5.56 rifles I checked closed on both the go and no-go, but not on the field. Good enough. Now I have one Saber Defense target barrel that is chambered for .223. On that barrel the go closed, but not the no-go or field, just what you are told should happen. So far I have been disappointed with this barrel, despite trying many hand loads and a 25 power scope on a solid bench rest my best groups have been just under 2 MOA.

Anyway I had a 20” DPMS bull barrel in inventory chambered for 5.56. I recently put it on an upper, and checked the spacing. The bolt would NOT close on ANY of the .223 gages??? Now everything I’ve read said if the barrel extension was put on by a reputable manufacture don’t worry about it. So I took it out and very carefully test fired it (with a string from behind a truck).
 Disclaimer “I don’t recommend this to anyone” but it shot just fine. I have used both .223, and 5.56 factory ammo with NO problems. In fact this rifle with a 9-power scope shoots circles around any I’ve shot. Well under 1 MOA. So I guess what they say about the tighter the chamber the tighter the groups is true.  
BUT what does this say about headspacing gauges???