Failed on Clymer Go Gage

[Lunker]

I have a 18" Mega Arms 5.56 barrel on a Midwest PX forged upper. It had several test rounds fired from it by the vendor. For giggles, I checked out headspace with my Clymer go/no go gages. The AIM Surplus bolt would not close on a Clymer Go gage. I swapped it out for my BCM BCG and it still would not close.
From prior searches here I have seen recommendations to simply use the field gage because that is what the TCM says to do. I was under the impression that just let me know when I was at maximum headspace on a worn rifle before it became dangerous.
Anyway, a bolt not closing on a GO gage indicates a short chamber. That seems like a bad idea on a semi-auto rifle. Any recommendations on how I should proceed?

[constructor]

I have a 18" Mega Arms 5.56 barrel on a Midwest PX forged upper. It had several test rounds fired from it by the vendor. For giggles, I checked out headspace with my Clymer go/no go gages. The AIM Surplus bolt would not close on a Clymer Go gage. I swapped it out for my BCM BCG and it still would not close.
From prior searches here I have seen recommendations to simply use the field gage because that is what the TCM says to do. I was under the impression that just let me know when I was at maximum headspace on a worn rifle before it became dangerous.
Anyway, a bolt not closing on a GO gage indicates a short chamber. That seems like a bad idea on a semi-auto rifle. Any recommendations on how I should proceed?

If a chamber is .001" short it will refuse a gauge but not make any difference in how it will shoot especially if you reload and adjust the size die to the chamber. It's obviously not too short because it chambers the ammo. As you shoot it more the bolt and extension lugs will mate and the headspace will grow a little. The go may fit after 50 shots.

[Onyx Z]

Factory ammo is headspaced a few thousandths below SAAMI min. Ammo manufacturers do this so their ammo will cycle 100% in all rifles. If you reload, you can size your brass to each specific chamber, even if they are fairly far out of spec.

This is why your rifle failed the test but will still cycle factory ammo just fine. Your rifle has a short headspace but is fine how it is. You can work around a short headspace (within reason). A longer headspace is what is dangerous.

[cd228]

Did you remove the ejector and extractor prior to gauging? was the chamber clean? Army uses a single field gauge, thats cut to accomodate the extracor/ejector. My COLT/Brownells gauge instructions to strip the bolt. Also, were you using the 5.56mm Go gauge (GO556NATO) or the .223 gauge (G0223REM) ? Not looking to sharp shoot you or any thing. I've also heard competion guns sometimes have tighter chambers. They have/had gauge sets that let you measure the headspace exactly.

[USMC_Anglico]

I'd be more concerned about it failing the no-go or field. Headspace grows with use and wear. Just don't put any M855A1 through it, that stuff is loaded HOT!

[Slvr Surfr]

What cd228 said. Did you strip the bolt first before trying it with the go/no go gauges?

Did you remove the ejector and extractor prior to gauging? was the chamber clean? Army uses a single field gauge, thats cut to accomodate the extracor/ejector. My COLT/Brownells gauge instructions to strip the bolt. Also, were you using the 5.56mm Go gauge (GO556NATO) or the .223 gauge (G0223REM) ? Not looking to sharp shoot you or any thing. I've also heard competion guns sometimes have tighter chambers. They have/had gauge sets that let you measure the headspace exactly.

[Lunker]

What cd228 said. Did you strip the bolt first before trying it with the go/no go gauges?

Hi, I did the second time around after having read CD228's post. It still failed the Clymer 5.56 Go gage.

[cd228]

Hi, I did the second time around after having read CD228's post. It still failed the Clymer 5.56 Go gage.

Hmm, i'd try a field gauge just for safety's sake. I'd also recomend reaching out to the barrell maker.

[Frac]

Hmm, i'd try a field gauge just for safety's sake. I'd also recomend reaching out to the barrell maker.

If it doesn't close on a go gauge, it certainly isn't going to close on a field gauge. What exactly will this resolve?

[cd228]

If it doesn't close on a go gauge, it certainly isn't going to close on a field gauge. What exactly will this resolve?

You are assuming that his go gauge is properly marked and sized. If the go gauge is properly marked , you are right and running the field gauge will tell us nada. Also, if he calls the maker and the maker tell him that they only use field gauges, the OP can say "it failed the field gauge too". Plus, to be honest, I'm Army and we only use the field gauge for headspace (we just did our arms room) so I just typed that in on auto pilot.

What course of action do you recommend?