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5/28/2026 9:38:40 PM EDT
I received it last night and inspected it.

It looks like the original pinned gas block had been removed and replaced with one using set screws (really not a fan of set screws). Even more interesting, it looks like new gas block has been set back closer to the barrel nut as I can see the groove from the original gas block about an inch forward of the new one.

What happened to this barrel? Should I be concerned?

5/28/2026 9:43:18 PM EDT
[#1]
Pics would help tremendously.
5/28/2026 9:59:11 PM EDT
[#2]
Inch forward?
Maybe a front sight block was replaced with a low profile block?
Disclaimer - OP is bad at knowing things, and might catch on fire.
Vet - Op MMAMA
Every other species kills off their stupid......we cater to them. -- spin-drift
Nobody ever called 911&said I just did something smart. -- TheFlynDutchman
5/28/2026 10:09:45 PM EDT
[#3]
Quote History
Originally Posted By Amish_Bill:
Inch forward?
Maybe a front sight block was replaced with a low profile block?
View Quote

Very likely the scenario.
5/28/2026 10:10:58 PM EDT
[Last Edit: TGH456E][Edited] [#4]
OP:
Could be just a smaller gas block, could be something else.
Markings? photos?

But was the "inch" a SWAG?  or did you actually measure it?  
That seems excessive as that'd be a pretty small GB.
And probably not capable of covering the port.
5/28/2026 10:59:42 PM EDT
[#5]
Quote History
Originally Posted By Amish_Bill:
Inch forward?
Maybe a front sight block was replaced with a low profile block?
View Quote

That would mean it wasn't the original barrel.

It is a Centurion Arms CM4 upper.

https://centurionarms.com/cm4-complete-upper/

Compared to the one illustrated, the gas block is right in the middle of the six M-lok slots instead of in view on the third slot from the front.
5/28/2026 11:18:50 PM EDT
[#6]
Quote History
Originally Posted By SCR556:

That would mean it wasn't the original barrel.

It is a Centurion Arms CM4 upper.

https://centurionarms.com/cm4-complete-upper/

Compared to the one illustrated, the gas block is right in the middle of the six M-lok slots instead of in view on the third slot from the front.
View Quote


From your description, it sounds like you have a carbine length barrel that once had an FSB installed, instead of the midlength barrel with lo-pro gas block that's in the listing.
5/29/2026 8:23:53 PM EDT
[#7]
Quote History
Originally Posted By cdholmes:


From your description, it sounds like you have a carbine length barrel that once had an FSB installed, instead of the midlength barrel with lo-pro gas block that's in the listing.
View Quote

Yep. The more I look at it the more that makes sense. A shame - I really wanted that upper.

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