Geissele mk4 adjustable gas block

**Striker6** · 07-15-14, 20:34

I'm curious as to which gas block guys are using with their Geissele rails. I'm specifically looking for anyone successfully running an adjustable gas block under the mk4 rail. I wanted to run a Syrac gen II adjustable, but they list it's height at 1.383 and the Geissele mk4 is listed as having an inner diameter of 1.35.
Thank you in advance.

**steyrman13** · 07-15-14, 20:39

I'm not positive, but I think you will be fine. That inside diameter should be the minimum which is the inner circular part but the block extends into the cross for lack of better words

**SpeedRacer** · 07-15-14, 22:54

Originally Posted by steyrman13

I'm not positive, but I think you will be fine. That inside diameter should be the minimum which is the inner circular part but the block extends into the cross for lack of better words

This. The inside of the "cross" from top to bottom is right at 2".

I'm using a MicroMOA Govnah (2 setting) with an MK4, it's a close fit but it works fine. I'm not sure how the Syrac compares in size.

**Striker6** · 07-16-14, 09:10

Thank you gentleman for the responses.

**Jwknutson17** · 07-16-14, 11:57

The SLR is smaller then the Geissele super gas block. The Geissele is the only gas block that I had to shave to fit under the BCM KMR rail. The SLR fits under the KMR with no modification. If the Geissele Gas Blocks fit all of there rails, the SLR will fit. Could not speak for Syrac, but I thought someone on here had it under a KMR. So you should be good to go with either the Syrac or SLR. The MK1 and Mk2 rails I have fit it, but not sure if there is any difference with the MK4.

**markm** · 07-16-14, 14:40

Originally Posted by Jwknutson17

Could not speak for Syrac, but I thought someone on here had it under a KMR.

That's me. Syrac fit, but one of the Keymod bolts had to be shaved for me to run a rail section on the bottom-front of the handguard.

**Striker6** · 07-16-14, 16:25

Thank you Mark. Your positive experience with the syrac was one reason why I'm going to try one on this build.

**BufordTJustice** · 07-16-14, 17:48

The Sentry 7 by SLR rifleworks has plenty of room. I have pix of it under a KMR in my thread review of it. It is tiny and light.

Originally Posted by Jwknutson17

The SLR is smaller then the Geissele super gas block. The Geissele is the only gas block that I had to shave to fit under the BCM KMR rail. The SLR fits under the KMR with no modification. If the Geissele Gas Blocks fit all of there rails, the SLR will fit. Could not speak for Syrac, but I thought someone on here had it under a KMR. So you should be good to go with either the Syrac or SLR. The MK1 and Mk2 rails I have fit it, but not sure if there is any difference with the MK4.