Rifle test fired fine but would not close/lock on a "GO" gauge (forster). This is with the ejector and ejector spring removed from bolt.  Also tried multiple bolts, same results.  Did not close/lock with "NO GO" as expected. Will it close after so many rounds fired? Thanks.

oops

Hi Snake,
I don't want to tell you something you already know but I can't tell from your post what your experience is, and don't want to assume wrongly, so I'll build from the base.

Headspace measures the distance between the face of the bolt and the point that stops forward motion of the cartridge in or at the chamber.
In an AR15 the critical parts are the bolt and the barrel extension.
If you have correctly checked headspace, and it sounds like you have removed the ejector, and you have checked multiple bolts, then you might have an out of spec barrel extension.
However, it is entirely possible to have a hard time with a Go gauge if the extractor is not removed, and I suggest you try removing both the ejector and the extractor and see if your problems persist.

If your problem persists, then you have a decision:  To shoot it anyway or not?
In answer to your question whether the tolerances will open up, the answer is "yes" but it will take many rounds (thousands).  If you really have a headspace issue you can run into serous problems with dangerous overpressure and bad things.  If your barrel extension is causing a headspace issue I would not use the weapon and would contact the barrel manufacturer.  They will want to know of such a situation.

If you find the problem resolves when you check the headspace without the ejector or extractor then you are golden.

Just for completeness, there are many who do not check headspace and would just tell you that if it closes on a round and fires and ejects then you are golden.  While I respect that experience and position,  I am enough of a geek that that does not work for me and I check headspace on every build.  

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Hi Rick,
Yes both ejector and extractor were removed prior to checking the head space. I manually cycled some dummy rounds, it fed and extracted with no problem. I had already contacted the manufacture, we'll see what they had to say. Thank you for the response it was very informative.

You should measure your bolts.
If the distance from the rear of the locking lugs to the face of the bolt is .153” (min spec) on a bolt that fails the Go gage then your barrel has a problem.
AFAIK the current US mil-spec for Go is 1.4646” and the SAAMI Go spec is 1.4636”, there is also an older SAAMI spec gage that is 1.4640”.

Thanks, never would have thought of doing that.

Measure your fired case headspace. Hornady's Lock-N-Load, RCBS Precision Mic or Mo DeFina's Precision mic work great and will give you a measurement when you resize your brass. Fired case measurement -.003" is considered the minimum shoulder set-back for use in a semi-auto.

Different headspace gages read differently from other brands. Your rifle closes on new ammo which isn't surprising, almost all of it comes from the factory shorter than it needs to be.

Manufacturing tolerances exist on both ends, the barrel maker's and the headspace gage maker and you may be seeing that in your circumstances.

All rifles need to close on a go-gage before it can leave the factory. The question becomes who's go gage did they use? If you think you have problem contact the barrel maker for resolution.