12.7 group buy Faxon gas block troubles

[grayfox]

Well, this 12.7 faxon build is getting frustrating. I have tried 2 0.750 gas blocks, one of them a BCM, and neither one fits, both "seem" too small. Apparently the nitriding process on this barrel has thickened the journal > 0.750. I tried heating the GB and no help. Then chilling the barrel and heating the GB, and I got one to slide partially on but it immediately became stuck, naturally out of position, and I cannot get it off.
I am used to chilling the barrel and/or heating the upper for the BCM uppers, but never have I had this kind of trouble with the gas block.

Heating both did not loosen up the gb... now trying to freeze them both.

If I have to take this to a GS to fix that's going to jump my costs, delay my build, and raise my ire.

Yeeeeesh.

I am certainly thinking faxon has major QC issues in this setup.

I've done 2 other faxon builds and did not have any gb trouble, actually, no troubles at all, with them.
This one is different.

[jonny rotton]

the first one i tried was too small too. i tried another one that i had and it fit fine. try another one!!

[grayfox]

I tried 2, different mfr's... that's my limit.
Took it out of the freezer, applied a rubber mallet and some oak 2x3 I have on hand and beat the GB off of the barrel.
Guess I will head out to find some lapping compound and try that on either the barrel or one of the GBs.

[ClutchAutomatic]

That's one reason why I like the clamp on adjustable design.

[Kswhitetails]

Mine was really tight. Diamond head set screw. I was rather surprised that there is no damage to the finish on the barrel after three installments, impressed with the seemingly hardened metal. Lap the gb, be glad for the good better than factory fit. I was surprised with the increase in work required to put this build together, guess I’m just happy with the silver lining that it’s a better build because of it.

[grayfox]

I'm going to hit autozone tonite after dinner and get some lapping compound. Not sure I want to go the clamp-on route, even the "low profile" blocks have only a little clearance on the bottom. They probably work fine, just I haven't gone there as of yet and don't want to write off these 2 gb's I have on hand...
So, yeah, ksw one of the gb's will get the treatment.
I've got everything else, except the red-dot is still inbound (tomorrow hopefully). But the rest I've got here.

[ClutchAutomatic]

True that, I've got a large handguard that can fit a suppressor in it.

[grayfox]

I inspected the barrel extension lugs and chamber, and cleaned the interior, not sure if I saw any burrs, maybe some steel "flashing", so I used some JB compound to polish them up a bit, everything there, so far, looks ok - I used a dental pick to probe around places where my finger couldn't get to. But I won't know on that (brass scoring) until I can send something downrange.

[Lastrites]

Nitriding should not add any thickness during the application, something else has got to be off, did you happen to measure the journal?

[BCHunter]

Measure the journal and ID of the gas block. On my Odin the gas block was out of spec, .743"

I was at the same point was trying to tap it on with wood and gunsmith 2 oz hammer. When the light went off and said something was not right.

[Popeye212]

Try freezing the barrel only. If you freeze both it's possible both will contract. Frozen barrel heat the gas block. Heat will make the gas block expand and may fit on the COLD barrel. My .02

[Bigs28]

Use clamp on.

[grayfox]

As a brief re-hash, it was difficult logically to conclude, IMO, that 2 gas blocks from 2 diff mfr's would both be too small, by the pretty much same amount if I judge from their similar almost-fit onto the barrel, sticking in the same spot, refusing to spin - both acted much alike -- what was the common item in this? the barrel's journal. I tried the barrel freeze/GB heat combo to get the gb on and it resulted in the GB going part-way on, then sticking in place, misaligned as well. That's where this thread commenced. The problem was that the barrel and GB were stuck together. I know that nitriding is not SUPPOSED to change the dimensions any, but well, here we sit. All my previous builds have gone barrel/gas block just fine, no problems. Either something was out of spec or the gremlins finally caught up to me!!

Now, to continue, I placed the entire barrel/stuck gb in the freezer to chill them, then with help of a rubber mallet and block of oak I was able to knock the gb down and off of the barrel.
Off to the Autozone and pick up some lapping compound. Using that compound and a 12-ga mop I lapped several times inside the gb. But I also did some lapping on the journal. Now finally at last I got the 2 to fit, still very snugly. The journal looks a little "bronzed" rather than the original dark choco-black, but they fit together, so that's my ultimate aim.
Rifle is now completely assembled but I am still waiting on my red dot... then out for the test firing (to see whether I will also have brass gouging or not...)...

[BCHunter]

Thank you for sharing your experience, it is always good to see solutions to problems.

When I had this issue it was easy to determine the gas block was out of spec, and was exchanged with the manufacturer. I was relieved that it was the easier of the 2 to exchange!
Look forward to the range report.

[grayfox]

I have to say this is a new one for me. I was quite frustrated, glad now to get thru it.
We'll see what tomorrow brings!