First build, barrel is marked 5.56.  Got the go no go gauges today, but they are marked .223. Wil this cause a problem?

What brand of gauges, and most likely no it will not be a problem.  

 

Forster

And forster is the brand that is a different dimension.  Waiting for somebody smarter than me, PFC should be along sometime, he find the headspace threads regularly.  

I think Forster is 1.4636” on the go and you need a minimum 1.4640" on a 5.56 civilian go, 1.4646" for a milspec go.  This is not gospel.  But I believe it is close the case.

5.56 no go gauge is slightly longer than a 223.  I can't remember the exact difference but most 223 no go gauges will close on a 5.56 chamber that is close to the max.  If the go gauge fits and it doesn't close on a field gauge  don't worry about it.   Most problems I have seen are with barrels that are short chambered and  the bolt will not close on a go gauge.  You can also put a layer of  scotch tape on the end your 223 gauge that will add a couple of thou.

Thanks for the helpful response guys, I really appreciated. Everything seems to be AA-OK.  Put the go gauge in and bolt closed then no go gauge and bolt doesn't close no matter how hard I pushed.  This is with the ejector pin/spring and extractor removed from bolt.  All that's left is to test fire it when time permits.

I have NATO Forster 5.56 gages that are:

Minimum-1.4636

Maximum-1.4736

I don't think that it makes any difference if it's marked 223 or 5.56 - it's the actual length assigned on the gage that means anything, but I'm not sure.

My old (35 years) Forster 223 REM Go gage is 1.4640”.
My current Forster 223 REM Go gage is 1.4636”.
My current Forster 223 REM No-go gage is 1.4666”.
My current Forster 223 REM Field gage is 1.4696”.

The last time I looked SAAMI chamber spec for 223 REM was 1.4636” min to 1.4736” max.
Mil-spec for 5.56mm rifles is 1.4646” min to 1.4706” No-go on a new barrel.
A 5.56mm chamber may fail a 223 REM No-go gage and still be in mil-spec for a new barrel in which case a 223 REM 1.4696” Field gage is close enough to work.
After all who would want a barrel that has 70% of the headspace range gone before the first shot.
I like my headspace tight so personally I am OK with the 223 REM 1.4636” Go for my 5.56mm AR’s.