BRT CustomTune Gas Port

BRT CustomTune Gas Port™




The BRT CustomTune Gas port reduces gas system flow and can correct for barrels with large gas ports that exhibit excessive gas drive.

The port is installed inside the gas block or FSB between the barrel and gas tube.

After installation, it requires no user adjustments or maintenance.

It cannot fall out, come loose or go out of adjustement.

The gas port is available with a variety of port sizes to meet many applications.



Installation requires removal and re-installation of the low profile gas block or front sight base.

Installation is relatively easy and may take less than an hour, start to finish.

Includes FREE SHIPPING.  Please allow 3-5 days for items to ship


Suggested Sizes:

5.56 11.5" CAR: .070"

5.56 16" CAR: .063"

5.56 16" MID: .076"

Please email for recommended sizes for specific applications.


Here are a few examples.  This 11.5" barrel had a large gas port.

It was very overgassed, cycled too quickly and ejected brass forward.

A CustomTune Gas Port was used to bring it back down to normal.

Function is now exactly where it should be and it shoots great.



The owner then wanted to run this same upper with the suppressor.

Suppressors add even more gas drive, so the gas port was swapped out with a smaller one.

With the smaller port to compensate for the suppressor, it functions just like before.


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Average Rating:


Reviewed by Jordan on
This is a great kit. I have an 11.5 SBR with a gas port sized at .076 and i chose the .063 gas port while using the VLTOR A5 system. Using the A5H3 buffer, it was much smoother with and without my Saker 556K. Super easy to install as i didnt have to drill out my BCM gas block, just tap the port and youre done. 10/10 will be using this on future suppressed builds.
Reviewed by Tom on
An effective and simple solution for over-gassed carbines. Save the money you'd have spent on buffers and springs, and apply this.
Reviewed by Tom on
I could have bought a case of ammo with the money I spent on buffers and springs. Fifteen minutes at the work bench, and my problem rifle now runs like a sewing machine (16" Stag M4 profile barrel, semi-auto carrier, 5.56 handloads at 3K fps). BRT's recommendation was perfect.
Reviewed by AddictedToPew on
Been trying to tame my mk18 (.082) for a while.. I tried h2 buffers, h3, etc.. and it might have helped a little but the .070 microtune gas port seriously made my rifle fun to shoot. It's so much smoother now. I could not be happier. So much better than adjustable gas blocks and bcg's.
Reviewed by Evan on
I built a new upper receiver for mostly suppressed use and wanted a smaller port than the barrel came with. The barrel I used is a 11.5" Colt FBI HRT barrel with an already conservative factory port size of .070. I ordered a .063 port insert and used the supplied tap to thread my Geissele gas block for the insert. Everything went smoothly and the rifle functions great both suppressed running a Surefire SOCOM RC2 and unsuppressed running 5.56 pressure ammo (IMI, CBC, Blackhills, etc). I'm using a Geissele Super 42 carbine spring and buffer in H2 weight in conjunction with an LMT Enhanced bolt and carrier with this setup. The rifle feels perfect with the suppressor and ejects consistently between 3:00-3:30. Without the suppressor I'm getting consistent ejection at 4:00-4:30 and the rifles recoil is very soft (Much softer than my 14.5 BCM midlength with a SF MB556 and H2 buffer unsuppressed). Temperatures were tested from 18 degrees up to 100 degrees without issue. I've yet to test .223 pressure ammo as I only run 5.56 pressure ammo, but even still these port inserts are simply awesome!

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