This is the latest from MARK at FAXON Customer Service (12/28/2017)...
There is a big difference in standardization between the AR15 and Ar10 platforms. Because of that difference, I recommended using the gauges for the tooling we use. We have run into this numerous times with both Clymer and Forster gauges. Not that they make bad parts, but there is a slight difference, and with the possible tolerance stacking because of the lack of standardization the only way to assure proper headspace checking is to use the PTG gauges. I feel that with a pass using the Forster field gauge that the firearm is safe to shoot.
And this is from AR15.COM:
Posted: 1/31/2016 1:37:27 PM EST
[Last Edit: 1/31/2016 1:40:16 PM EST by RogueNathan]
Originally Posted By Vicious_138:
I have finally gathered all of my 308 build parts, so I took my bolt and barrel to a gunsmith to check my headspace.
I have an 18" Faxon barrel & an AIM nitride BCG. I removed the extractor and ejector before heading to the gunsmith. The bolt easily closed and locked on the go gauge, so then he tried the no-go gauge. The bolt closed and locked on the no-go, you could even wiggle the bolt a little while it was locked. Not good
My smith didn't have a field gauge, but he did the scotch tape trick on the no-go gauge. The bolt would not lock with the tape on the no-go gauge.
He then measured the bolt from the front of the lugs to the bolt face, and it was a consistent 0.125. I don't know know if this is what it should be or not.
Unfortunately I do not have another 308 bolt to check. So something is out of spec, but I don't know which.
I have emails out to both Faxon & AIM, so I will update with responses. Hopefully I can get this taken care of soon, it has taken me a while to get all the parts together, and now I am anxious to get it done. This is also being built on an 80% Arms 80% lower.
There are a few things that it could be related to, of which one of them not mentioned is the depth of the lugs themselves on the bolt, which is also a component.
The crazy part of the AR-15 & AR-10 specification is that there is only .003" from "Go" to "No-Go" and .005" total allowed deviation on the length of the bolt lugs itself (which does not account for the depth of the co-bore, which also has allowable deviation). All combined, this is what necessitates the need to head-space individual bolts to barrels.
We machine and check for head-space using tool steel bolts that we custom ground (the most accurate form of machining, outside of EDM) to check the head-space. Generally, this gives us confidence the barrel is not the issue
My assumption is that you are seeing tolerance stack between the bolt, co-bore, chamber depth, etc. This is common throughout AR's. The recommended solution is assuming the chamber is correct (we are making that assumption based on our quality procedures), a simple swap of the bolt closer to its nominal spec will bring you into nominal overall.
Given it does not rotate with scotch tape, you are at least .008" from field which is safe and serviceable (the rifling will wear prior to the chamber going out of spec), should you choose to keep the parts combination as stated.
Last piece to ask of a gunsmith is that they are using .308 WIN head-space gauges instead of 7.62x51 and the printed length on the gauge?
**OOPS! Noticed it was .308, which is also the same general facts. Posted updated to reflect the differences.
The Director at Faxon Firearms
Ask us any questions or drop me an e-mail: Nathan@FaxonFirearms.com
