Gas block canted

[gnumadic]

I don't think this is a major issue given the port size of my gas block (bigger than the barrel port), but I'm posting because the tolerance on my handguard (Aero Precision ATLAS S-One) is super tight AND I am wondering if this is a common issue or not.

Barrel is the 18" Faxon Group Buy. Gas block is a CMT J.A.G. that I got for just shy of $20. All the reviews seemed good. Now I'm wondering if I should have spent a little more. Just eyeballing the installation it looks like the block is slightly canted.



I used an SLR dimpling jig. The below pics show the position of the gas port and dimples using a toothpick.



And here I'm sticking an allen wrench through the gas hole and set screw hole, pushing to one side and then to the opposite.



Anyone else have this happen? At first I thought it was the barrel--gas port and barrel extension being out of alignment--but now I am pretty sure it's the gas block set screw holes that are machined a little bit off-center.

[Kswhitetails]

Does it shoot? I'm not sure I'd be inclined to change anything if it shoots well. Looks like you have more than enough space under the guard. How rough do you intend to be? If I were to guess, I'd be willing to bet it'll run fine. How anal do you want to be? You could send it back and probably get another block - from a different vendor - but if it shoots, why?

That being said, if you're like me, it'll eat at you till you fix it. Haha..

[gnumadic]

Does it shoot? I'm not sure I'd be inclined to change anything if it shoots well. Looks like you have more than enough space under the guard. How rough do you intend to be? If I were to guess, I'd be willing to bet it'll run fine. How anal do you want to be? You could send it back and probably get another block - from a different vendor - but if it shoots, why?

That being said, if you're like me, it'll eat at you till you fix it. Haha..

I have not shot it yet, which would be a good next step. It's a hunting rig so no serious wear and tear intended. But yeah, you've totally got me pegged. Anal AF. LOL.

[bj139]

The gas block is not a precision aligned part which is what the extra large hole in the gas block is for.
If the barrel port is not obstructed by the gas block it should make no difference.

[Schrambo]

I just send a Faxon 20" barrel back for a mis-aligned gas port hole. It was so far off, I couldn't get my handguard on over the lo-pro gas block...

Yours looks like it should still work well, I'd shoot it and see...

[bj139]

I have a BHW barrel with the gas port not directly on top and posted somewhere on ar15armory about it.
It was a non-Grendel related barrel so i thought I should not post it here.
I have not shot it with a gas block so I can't report my experience with that.
I thought the gas port may have been drilled so it was in a groove but someone working for BHW said that was not so and it should shoot fine anyway.
Apparently this is industry practice, at least with two companies.

[Crusty]

If it were mine and I looked at the gas tube tail in the receiver and saw that the tube wasn't exactly parallel with the receiver I'd get a new gas block which was manufactured correctly. With a canted gas tube there's a higher probability of the gas key not seating correctly onto the tube and possibly causing malfunctions.

[bj139]

If it were mine and I looked at the gas tube tail in the receiver and saw that the tube wasn't exactly parallel with the receiver I'd get a new gas block which was manufactured correctly. With a canted gas tube there's a higher probability of the gas key not seating correctly onto the tube and possibly causing malfunctions.

I bent one or two tubes sideways a bit to get them centered inside the receiver. They come bent anyway.

[Kswhitetails]

I bent one or two tubes sideways a bit to get them centered inside the receiver. They come bent anyway.

Aye aye! It's a little bit of trial and error and forget it. If you decide it's not worth the effort/expense/wait to make it "right".

[gnumadic]

Thanks everyone for the feedback...it's all very helpful. I posted this because my previous experience with a Ballistic Advantage gas block and barrel was perfectly aligned--and it was my only experience. And when I noticed the block on this Grendel build was canted, it took me a while to determine if it was the gas block, the gas port on the barrel, or my dimpling jig. It also made me wonder if I had prematurely dimpled the barrel (i.e., should I have tested the alignment prior to dimpling?). Best I can tell, the gas port on the Faxon barrel is aligned with the dimple on the barrel extension...and the SLR dimpling jig is also accurate.

Last week I was buying an SLR adjustable gas block from Brownells (for build #3 in 300 BLK) and decided to throw in one of SLR's Sentry S7 non-adjustable gas blocks. It was only $36 and I figured I could either return it or save it for a future build. It also happens to have the same set screw spacing as the CMT jig at .400". It came today and the S7 fits great.



A few things I noticed about the SLR vs the CMT:

1. The SLR was noticeably more snug sliding it onto the gas block journal
2. The gas tube (Spike's Tactical) had much more friction going into the gas block (on the CMT it wanted to spin/rotate easily)
3. The gas tube roll pin went into the SLR block with significantly less effort (...I didn't ruin any pins!)

Again, my experiences are limited but would it be fair to say that the SLR block was machined to much tighter (or accurate) tolerances? To me that seems like a good thing considering it's part of the gas system. I don't mean to knock CMT's products (maybe I just got a bad one), but in hindsight I don't think it was worth trying to save $15. Perhaps there are better places to save coin on a project.

The other thing I'm learning is that mil-spec has some variance and sometimes mixing and matching parts exacerbates those variances. For example, I had initially purchased a Stag Arms upper receiver to match the lower receiver (plus it was on sale!) However, the Faxon barrel extension was on the low side of mil-spec and the receiver was the opposite (perhaps slightly out of spec). I could put the pieces together and the receiver would just fall off if I tilted them. Rather than go to extreme bedding/shimming measures, I returned the receiver and bought a BCM since they make theirs with a tighter inner diameter for the barrel extension. I did not have to apply heat...just a little tap with a rubber mallet. Hoping all that helps make this rifle shoot a little better (and not just fuel my perfectionist tendencies).

[LRRPF52]

Most important things are:

* Gas ports align between the block and the barrel
* Gas system doesn't have leaks
* Gas tube aligns with the carrier key

Most of the time, there is a tiny bit of cant to the gas block when the tube is aligned optimally with the carrier key on home builds.

If you were the manufacturer and could control your tolerances, you could address this as a total system designed to fit how you wanted.

Since you are a retail customer left with whatever parts you get, you get to play fit and hope more.