AR15/M4 Gas Block: The Simplest Option

A common and popular modification to M4/AR15 platform these days is to install a narrow diameter tube style free-float rail (or any other long rail) system to replace the stock hand guards. If you are buying a new upper receiver, it is fairly simple to specify a low profile gas block. However, if you are starting with a service grade carbine like the excellent Colt 6920, you are going to have a standard A-frame type front sight base. What to do?

One option is to replace the front sight base with one of many viable aftermarket, low profile gas blocks. The down side to this is if you want 100% confidence, you will want to get it pinned. Unless you have access to a machine shop, this means paying someone to do it for you. The other option is much simpler. 15 minutes with a hacksaw and you can chop off the A frame along with the bayonet lug and 6 o’clock sling mount. Clean it up with a Dremel tool and a file and you are all set. I blasted and parkerized mine, but if you don’t have access to these tools, cold blue will work in most environments. This is an M4, not a custom 1911 so don’t sweat every little cosmetic detail.

This option will leave you with a lightweight, low-profile and ridiculously strong gas block since it will be held in place by not one, but two taper pins.

This entry was posted in Long Guns, Weapon Modifications by Tim Lau. Bookmark the permalink.

About Tim Lau

Tim Lau has over a decade of experience as an end user, armorer and instructor. He has worked for several well known firearms training organizations, and holds multiple firearms instructor certifications. He owns and operates 10-8 Consulting, LLC, which provides industry consulting services as well as marksmanship and specialized firearms training to qualified civilian, law enforcement and military personnel.

13 thoughts on “AR15/M4 Gas Block: The Simplest Option

  1. I did this for a rail a while back. My first thought was hoping no one saw the ghetto gas block underneath the rail. It’s good to know that I’m not alone in my money saving ghetto-rig fixes. Thanks for sharing.

  2. A friend hacked his, then cleaned it up with a Dremel (don’t overheat it), and you really can’t tell that it’s a cut down A frame.

  3. Being I suck with tools (and my recently purchased Sawzall is something the government should be more concerned with me owning than guns…), I had Ken Elmore do this with a couple of my project guns several years ago. They, of course, look like custom pieces with Ken’s work. The biggest benefit is that by using the original, properly fitted and pinned gas block, the rifles done this way have run very reliably and with zero issues with very high round counts. I also have never worried about them coming loose or having any gas system issues.

  4. Mine took an extra bit of grinding to get it to fit under a narrow Troy Alpha handguard with light attachments but provided a rock solid sense of satisfaction when done! I hit mine with some OD Aluma-Hyde II I had lying around. I like seeing the bit of green thru my handguard reminding me of what’s under there.


  5. Forgive my ignorance but when swapping out a handguard doesnt the gas tube and gas block have to be removed in order to install a new barrel nut?

    • Yes, but you can simply reinstall the gas block and tube after replacing the barrel nut. And some free float handguards (like the excellent Centurion Arms C4 Rail) work with the existing GI barrel nut so you can skip this step.

  6. Tim,

    Can you tell me what make and a source for that 9:00 o’clock sling bracket on the lower pic? I’m assuming it is clamp on and aftermarket. Thinking it might be a good solution to my DPMS Oracle plain gas block problem.

    Happy shooting, dv

  7. I recently bought a 12″ hand rail at the local gun show. The bastard that sold it promised me that it would fit my M4. I had no clue that the gas block was attached to the sights. My local guy told me it would not work without getting rid of my sight. I love the front sight, just because when I see an AR or an M4 it is what gives the gun an identity.. I’m not taking a saw to any of it. Am I screwed, how much is a barrell with a block and the sight made for a 12″ handguard?
    Am I screwed

    • Uh, the front sight post gives your M4 identity? Ok, whatever floats your boat. One of the nice things about the M4 platform is that there are so many options for modification that you can have it your way. The easiest solution if you wish to use the hand guard you purchased is to either cut down the gas block as shown, or have an aftermarket one drilled and pinned to your existing barrel. I am not a fan of the clamp style or securing only with set screws. Or you could sell the hand guard you purchased and get an extended hand guard with a pocket cut out for the front sight post like the FSP rail from Centurion Arms. As with any purchase, research first before you buy. I don’t recommend taking advice from most gun store clerks since if they truly had any background they wouldn’t be working at a gun store for a living. There are exceptions but they are few and far between.

      • Thanks for the advice. I had come across the type your recommend. I think that’s gonna give me the best result, your right about the versatility. And you can tell, I’m new with my M4.
        Learning the hard way,

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