Centurion Arms Tabbed Gas Block





Most of the AR-15  barrels from Centurion Arms now come with a notch that is milled TDC in the shoulder of the gas block journal.  This notch aligns with the gas port of the barrel and is intended to interface with the Centurion Arms low-profile “tabbed” gas block.  





A precisely machined “tab” on the Centurion Arms gas block dovetails with the notch in the shoulder of the gas block journal to align the gas block with the gas port of the barrel.  You can still use a standard 0.750” low profile gas block (or an A2 front sight base) with the Centurion Arms barrels, but you won’t want to, as the tabbed gas block is a work of art.





The notch in the shoulder of the gas block journal has a nominal width of 0.1020” as measured with Mitutoyo digital calipers.  The tab on the gas block has a nominal width of 0.1014” as measured with a Mitutoyo micrometer.  This creates a transition fit with a clearance of only 0.0006” and there is no rational play with the gas block mounted on the barrel.





With the tabbed gas block pressed against the shoulder of the gas block journal of the barrel the set-screw threads of the gas block are precisely aligned with the dimples in the 6 o’clock position of the Centurion Arms barrel.








The Centurion Arms tabbed gas block system makes the process of precisely aligning the gas block with the gas port of the barrel practically foolproof.  





The Centurion Arms 0.750” low-profile tabbed gas block weighs 1.1 ounces.  As mentioned above, the version that I reviewed is drilled and tapped for use with two set-screws to secure the gas block to the barrel.  The US Army Marksmanship Unit discovered years ago that pinning the gas block to the barrel can degrade accuracy.

The bore of the tabbed gas block has a gauged diameter of 0.7495”.  When mated with the Centurion Arms barrel that has a nominal gas block journal diameter of 0.7493”, these components have a tight transition fit with only 0.0002” of clearance.
 
The gas tube channel of the tabbed gas block has a gauged diameter of 0.1801” and when paired with a Centurion Arms mid-length gas tube that has a diameter of 0.1797” at the proximal end, these components create yet another snug transition fit with only 0.0004” of clearance.  These tightly toleranced components all contribute to a very efficient gas system and it’s quite refreshing to see a company that produces AR-15 components that hasn’t let their quality control deteriorate over the last few years.


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I love reading your technical write ups.
Awesome as usual.
Thanks for taking the time to do these write ups.

Big fan of Centurion Arms.  I feel like they are a bit underrated.  I have been very happy with their barrels, receivers, etc

I’m sold. Thanks for writing this up.

Centurion Arms is one of those companies that isn’t massive in terms of marketing but those who know about them know that they are one of the exceptionally good manufactures out there with excellent attention to detail and quality control.

Everything Monty does is pure quality. I totally echo the post above, Centurion is right up there with the best in terms of quality and consistency.

They make a damn good barrel. One thing I’d like to mention is whatever barrel extension they use on every one of my recently purchased barrels has been very tight in Colt and dogbone uppers. Zero wiggle at all.

Are there any drawbacks to the shorter set screws?

I've recently dropped in DD and Centurion barrels into Centurion receivers. It's not a true thermal fit but it's damn close. Requires a good bit of motivation to seat and there is zero perceivable slop on any axis.

So exactly how long are the set screws? I ask because the CA block I got the screws were only 1/2 as long as a standard GB screws as they machine the bottom of the GB so thin to clear rails. About 2 1/2 threads long is all they were. Didn't look very confidence inspiring to me. Not much metal to go into the dimples.

This video explains it all.

Would this really matter much if you torque down and rocksett the gas block screws? All my centurion barrels are pinned so no idea just curious.

Not an issue in my experience.  I have three unpinned Centurion barrels with their low-pro tabbed gas block installed and rocksett has held the set screws in place without any issues whatsoever.

That video explains nothing bc it’s a non issue. Someone posts a video on YouTube (wherein they admit they’ve been drinking) and it becomes valid info that you follow? I’ve seen a large number of CA low profile gasblocks that were set screwed only have the shit ran out of them on full auto and there’s never been any issues whatsoever.

Yea,  the guy in the video is a bag of wind and doesn’t seem to care much for Monty for whatever reasons.

However,  he does illustrate the sacrifices made to make such a low-low profile GB.  2-3 threads isn’t all that difficult to strip.

No, it doesn’t "illustrate" that.  If someone doesn’t like the 1/8” set-screws that come with the tabbed gas block, they could just spend a whopping 58¢ and buy two 5/32” or 3/16” set screws (which is the length often found with low-profile gas blocks).  Or, go ahead and use a gas block that doesn't have enough clearance.  It's not like I'm receiving royalties for every tabbed gas block sold.





The Badger Ordnance TDX gas block is even thinner than the Centurion Arms tabbed gas block and Criterion sells the TDX gas block as an add-on when purchasing their CORE barrels.  Seen a lot of failures of the TDX gas blocks?





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Excellent point.  You’re  literally a walking data archive.  I have no personal experience with either gas block but I will admit,  I do have experience stripping fasteners with minimal threads, care must be taken.  I do see now the provided set screws look to be counter sunk.

FWIW,  I think Centurion produces great products,  simple and effective….without all the glitter.  Not at all was I reading your post as a plug…..

Why does there appear to be a relief cut on the .750” journal, in front of the notch?

Any concern of gas leakage there? In theory it shouldn’t, but it is close to the port.

Attached File

My God, that guy is cringe.

OST

I have always been curious about the relief as well but not quite enough to ever call and ask.  

Cut too deep on that specific example(s)?

Molon, do you have any recent production CA barrels? I'm a longtime fan/customer of CA, but read that recent barrels have larger gas ports than older ones. Was wondering if you could take a measure? Just a curiosity at this point.

Definitely not that because I have three virgin barrels with them and two in use with that recess.  All five of my barrels have it.

I have a few but they are two years old.  I assume you are referring to barrels manufactured in the past six months?

Honestly unsure. My barrels are from almost a decade ago and have smaller gas ports than what is listed on the website, so not sure what has changed and when. I now see people posting anecdotal, undated port sizes inconsistent with (larger than) the numbers on the website, so I'm not sure what is the real number anymore.

I thought the guy in the video is OTDR?

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Now start putting tabs/ notches on scopes

That's exactly what I thought. The video was 20 minutes old when I clicked the link.

I suppose it may have been? I guess the thought never crossed my mind that someone would make a YouTube video crybabying about something like that.

As soon as the OP said, “precisely aligning the gas block with the gas port of the barrel practically foolproof.”

I could not help but think of the old saying, making something idiot proof only makes a better idiot.  

Somebody somewhere will manage to screw up installation and start bashing CA for making something in search of a problem.

1. I wish more people would use keyed gas blocks/barrels. 90% of them can’t be bothered with the 30 seconds to dimple a barrel though so not holding my breath.
2. That YouTube rant might be one of the cringiest things I’ve ever seen posted in tech.

Every bit of this. I have several of his barrels, various rails. First class all the way.

Creepy as fuck.

Sig put an alignment line on the side of the Tango 6. Made mounting it up very easy.
Attached File


The guy bashing Centurion Arms on video was giving off that guy that takes something apart and then when they reassemble it incorrectly, blames the manufacture vibes. The whole point of shortening that part of the GB is to make it fit tighter rails. While I prefer my blocks pinned, I do have rifles with set screws and they seem just fine. I can’t imagine having a couple fewer threads is going to make a difference in that area.

You could always use longer has block set screws. If they stick out a little it isn’t going to hurt anything. I buy my gas block set screws in bulk packages of 50. Same goes for all the roll pins, detents, springs etc..

The gas port sizes are listed on their website. IMO I wouldn’t say they are “large”. All of my Centurion barrels - so far just an 11.5 FBI and 12.5 LW - have been well gassed.

By well gassed, my 11.5 FBI ejects brass at 3 o’clock with a DA Sandman S on it.


ETA: That probably wasn’t much help, but I have no reason to believe they’d lie about the gas port sizes on the website

I want to know if any gasblocks have come out of alignment under a rail after being loctited in place with a dimpled barrel? It seems to me that the gasblock is pretty well protected under there and that with a good dimple and red loctite, it should be there until you decide to purposefully remove it. The alignment issue of gas port and gasblock seems mute as the hole in the gasblock is 10-32 tap size and the gas port in barrel is much smaller. You have to really get that sucker canted to block the hole in the barrel.

i have bought two over the past year and all have measured with what they have on their website with my pin gauges, buy with confidence they will be correct.

https://centurionarms.com/

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35% off 6mm ARC Barrels, 25% off all other barrels, and 30% off C4 BCGs.

I ordered a 11.5 CHF barrel inch gas block and polished feed ramps. I will post accuracy results when I have them.

a recently purchased Centurion Arms Enhanced SOCOM barrel . . .




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Nice!  I've been thinking how awesome it would be if you tested one of these, they check all the boxes of things I like in a barrel (mid length gas, no M203 cut, heavier than .gov under handguards, chrome lined)

Larue used to do something similar with the PredatAR barrels. Tabbed gas block and set screws (they have 3).

That I didn't know. First I'd seen was the CA.

Thanks for that info. Honestly, I've long wondered why journals / blocks were not milled/ keyed. EZPZ, no dicking around. Cost analysis I suppose.

Colt Canada/Diemaco does that with the L119A2 uppers (and probably the monolithic MLOK uppers) but they use one tab on either side of the gas block. It's a solid arrangement either way.

It's just an artifact of their milling process.




No.  The gas port of the gas block has a diameter of ~0.157" and doesn't communicate with the artifact and as I stated in my first post, the Centurion tabbed gas block forms a transition fit with the gas block journal of the Centurion barrel.

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No.



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I'll be slapping one of their tabbed GB's on this weekend.  I have one of their CrMov (non-CHF) LW barrels with FSB that shoots really well.  I want to FF & keep the FSB viable so the tabbed GB was a no-brainer.  I have .750 lo-pro GB's but ordered the Centurion part largely due to this thread.

Good idea, and should become the standard imo.

Swapped out last night/this morning.  Pretty slick - thanks Molon!  Predictably the rear taper pin groove interfered with the aft set screw on the GB.  The tab keeps it from rotating though so easy-peasy.  I didn’t notice when I bought it but Centurion dimples their FSB barrels also so another BZ to them.