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Posted: 11/13/2025 3:38:27 PM EDT
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I purchased a Faxon big gunner barrel, and a Brownells hard chromed 308 bcg to complete it. I’ve got a set of Forester 308 go/nogo/field gauges; go is 1.6300, nogo is 1.6340, and field is 1.638. Note - the barrel is NOT mounted in the upper. And sadly I don’t have an AR308 bolt disassembly tool to remove the ejector  Anyway - manually manipulating the go gauge and the bolt, it can chamber and lock. The nogo will ALSO allow the bolt to lock closed. It will NOT lock on the field gauge however. My understanding is that it’s not a huge problem if it’ll close/lock on the nogo; is my understanding correct? It would be a problem if it locked on the field, but not a big deal with the nogo? For 308 at least? And, would the results appreciably change if a) I were able to remove the ejector, and/or b) if the barrel were mounted and torqued into the upper? Thanks! |
"Oh, bother," said Pooh, as he pulled the pin on another grenade...
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Go and No Go are gun builder gages. The Go is minimum headspace. The No Go is the max a new gun should have out of the factory. Field gage is the actual failure of headspace where a firearm should be pulled and reworked. You may have missed the drag feeling with the No Go due to the spring pressure. Pulling an ejector from the AR15 is child’s play. I am assuming the big AR is the same but with a bigger spring. If it’s the same pressing the ejector with an empty case and hold it while drifting the ejector retaining pin with a small punch. To pass the NO Go gage you just need to detect the drag, it doesn’t have to be a hard interference. But when it comes down to it between Go and Field is Fine. The worry is if you set up close to field then with break in you may exceed the Field sooner than a good service life should. |
The only hyphenated names I like are cartridge names......30-06, 30-40, 38-55 etc.
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Originally Posted By SteelonSteel: Go and No Go are gun builder gages. The Go is minimum headspace. The No Go is the max a new gun should have out of the factory. Field gage is the actual failure of headspace where a firearm should be pulled and reworked. You may have missed the drag feeling with the No Go due to the spring pressure. Pulling an ejector from the AR15 is child’s play. I am assuming the big AR is the same but with a bigger spring. If it’s the same pressing the ejector with an empty case and hold it while drifting the ejector retaining pin with a small punch. To pass the NO Go gage you just need to detect the drag, it doesn’t have to be a hard interference. But when it comes down to it between Go and Field is Fine. The worry is if you set up close to field then with break in you may exceed the Field sooner than a good service life should. Agree with the above. Closing on no-go is safe, but may mean reduced barrel life. Between “break-in/settling”, wear, and throat erosion, you may get to failing Field faster. Now, if the barrel already has the extension mounted, as I understand it, there’s not much you’re going to do about it unless you try to return/exchange. ETA: shorter life is still in thousands of rounds, so I wouldn’t worry about it. |
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Is your barrel chambered for .308 or 7.62 NATO? They aren't the same. 7.62 NATO has a more generous range for acceptable headspace. Stacking of tolerances between different manufacturers of parts can cause variances as well. The main thing to watch for is case stretching or even case head separation. Had a case head separation with a M1A that was on the long side for .308 with Fed Gold Medal Match. |
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Matt
Matt
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Originally Posted By 1811GNR: Is your barrel chambered for .308 or 7.62 NATO? They aren't the same. 7.62 NATO has a more generous range for acceptable headspace. Stacking of tolerances between different manufacturers of parts can cause variances as well. The main thing to watch for is case stretching or even case head separation. Had a case head separation with a M1A that was on the long side for .308 with Fed Gold Medal Match. Yeah - I know 7.62 has a more forgiving chamber tolerance; that was why I got these specific gauges in the first place - I got them to help calculate FAL headspaces when I was big into FALs  Faxon just says "308 chamber" but ...who knows. Criterion advertise their M118LR chambered barrels as being safe for both 308 and 7.62; if Criterion made a 12-14" barrel I'd have gotten one of those. I have a Criterion M118LR rifle gas 18" barrel in my other AR308/M5 which is pretty nice. Sadly not a whole lot of ~12-14" barrels in 308 out there. Edit - that aren't thicker than a 1/2 ton truck axle. So this was the one I ordered from Brownells: https://faxonfirearms.com/faxon-duty-series-gunner-profile-13-9-mid-length-308-win-ar10-barrel/ I'm not super fussed about it, I mainly just wanted to make sure my understanding of things wasn't wildly off base. As another poster mentioned - it was a little tight closing the bolt on the nogo, even with the ejector still in place; closing on the go was very easy, closing on the nogo took a bit of effort, and it wasn't getting anywhere near to closing with the field gauge in the chamber. The other "weird" thing is the ejector in the Brownells BCG is rounded, not square like a normal AR ejector...I guess I'll find out if that means anything significant when I get the gas block and tube installed and can test it out at the range
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"Oh, bother," said Pooh, as he pulled the pin on another grenade...
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Originally Posted By Evil_Ed: The other "weird" thing is the ejector in the Brownells BCG is rounded, not square like a normal AR ejector...I guess I'll find out if that means anything significant when I get the gas block and tube installed and can test it out at the range That's actually a good thing. AR10's are notoriously hard on brass and a rounded ejector will have a harder time gouging the brass than one with a squared off edge. It's normal to work over a new bolt and remove sharp edges in key locations but Brownell's has already done that on the ejector. Gouging usually happens when the bolt is unlocking a bit early and the brass hasn't shrunk down and released fully from the chamber. Now if you don't reload yourself, there's not benefit but it's not a detraction either. On the headspace thing, a "larger" head space can also be beneficial for more case volume. But that's a different animal for the experienced reloader. |
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