Gas Block and rail question

[BamaBrad]

Ok, continuing on with the build wanting to get a few opinions as I am getting a couple different answers. I am getting a Criterion barrel from CLE and the gas block is .936. I am wanting to use the Geissele MK8 rail. One person from Geissele said the barrel extension or shoulder didn’t need to be more than .95”. I called back to CLE and explained that to them and he said they measure .98”. I called back to Geissele and got someone else and told them that and he said that should be fine as their nut is 1”. Will I have a problem using this rail with this barrel.

Also about the rail the gas block they are using is .936 the I.D of the rail is 1.3”. I can’t see where I would have any problems using this rail with this size gas block but I have never ran a gas block this size?

One last thing, for now, I am leaning towards the WMD BCG. Besides the reviews anyone have any comments on these? Thanks for any help.

 

[BamaBrad]

Well I know another member started a topic on the similar question on the gas block and still curious on both but now more or less the WMD BCG. Still researching the gas block and Geissele rail.

 

[longshot2000]

I am confused. What are you measuring? Are you using a 0.75" journal gas block? Does the gas block need to go under the rail? Your minimum clearance on a Mk8 rail is about 1-1/4" through the center line of the barrel bore, but many times the critical distance is at the with of the top of the gas block, which is why you see "low profile" gas blocks having a taper at the top.

What gas block are you using, and why not pick one that easily fits? If you are getting a Mk8 rail, use the Geissele low profile gas block and have it pinned. It comes in SS in the white, and SS blackened.

If it were me, I would send the gas block and the bolt to Frank to have him headspace the bolt to the barrel, and also to pin the gas block. I would also choose a quality bolt. I am not sure what it is you like about WMD, but if you hare having a custom barrel, get a bolt that is known for great service. I have no idea bout the bolt you chose, but I work with LMT and Youngs for marksmanship, and Colt, Daniel Defense, BCM and Toolcraft for durability and tactical use.

 

[BamaBrad]

Thanks for the reply. I can’t remember the guys name that I spoke with at CLE I think Frank answered and I asked for the other guy because that’s who I spoke to earlier but he said he could go with the .875 gas block if I thought the .936 wasn’t going to work. It is their gas block they are providing he didn’t say if it was low profile or not. I wanted him to install the gas block while he was doing the barrel.

 

[AZgeek]

If you ever consider adjustable gas blocks you gotta be careful. For example I have a .8750 proof carbon fiber barrel I just put on my 6.5 Grendel AR15. With the Superlative block, I had to upsize to 1.60 ID Owden Works rail system. Just barely fits and in your case you have a larger barrel. I would think a 1.60" ID would be required even with a low profile block.

 

[longshot2000]

I do a good amount of work with CLE. They are one of the best barrel shops out there. I also work with Criterion. Great barrel company. So far, so good. You can use whatever gas block you want, and you can send it to CLE, and they will pin it for you.

I am not sure what your gun is to be used for, or the caliber. A Mk8 rail is a lightweight rail, but you want a large gas block. For most configurations, a 0.750" journal is just fine. If you told me you have a 24" barrel, I might change my mind, but probably not, since the rail you want is 15" maximum. If CLE is recommending a 0.875" journal, they have a little internal bias for extreme accuracy competition rifles, and if that is what you want, then you might want a round free floating tube and not a rail.

Again, if it were me, I would use a 0.750" journal and a Geissele blackened low-profile gas block.

You might be making this more complex than it needs to be.

 

[padom]

Unless its a very low profile non adjustable gas block then it wont fit under the MK8. I have a MK8 and the only gas block I got to fit under it was Geissele's low profile gas block and a Superlative Arms which was VERY close but did clear. SLR, Seekins, etc. all hit on the top left side of the gas block.

I prefer a good bit of clearance around my gas blocks so there is no chance of it hitting the handguard and causing flyers. The YHM TJ Competition and Seekins SP3R V3 are both very solid handguards with a ton of clearnance around SLR/Superlative/Seekins gas blocks.


https://yhm.net/accessories/forearms/tj-competition-series.html


http://www.primaryarms.com/seekins-precision-sp3r-v3-keymod-modular-rail-system-15-sp0010530025

Currently on sale at Primary Arms for $139.99

 

[demolitionman]

Tag for reference.

 

[BamaBrad]

I do a good amount of work with CLE. They are one of the best barrel shops out there. I also work with Criterion. Great barrel company. So far, so good. You can use whatever gas block you want, and you can send it to CLE, and they will pin it for you.

I am not sure what your gun is to be used for, or the caliber. A Mk8 rail is a lightweight rail, but you want a large gas block. For most configurations, a 0.750" journal is just fine. If you told me you have a 24" barrel, I might change my mind, but probably not, since the rail you want is 15" maximum. If CLE is recommending a 0.875" journal, they have a little internal bias for extreme accuracy competition rifles, and if that is what you want, then you might want a round free floating tube and not a rail.

Again, if it were me, I would use a 0.750" journal and a Geissele blackened low-profile gas block.

You might be making this more complex than it needs to be.

I’m not trying to make it complex, I am just looking for help. You seem knowledgeable in the area especially working with CLE and Crieterion. I am doing my first “build” (5.56/.223). I am wanting the “best” barrel for the money type deal and after many recommendations to CLE I have 99.9999% got it decided on a barrel from CLE. It is a medium heavy barrel and he said normally he would put a .936 gas block on this barrel and I was concerned with running a rail with that size gas block then he said he could go to an .875. I don’t think a .750 will work with this barrel from the conversation I had with him.

Just from lurking around here I have gathered some great stuff and after buying AR’s I am ready to finish building mine and want it to be the best I can make it. I really do appreciate your help as well as the help from others.

I am also up for other suggestions, barrel wise. This will be my coyote/target/fun gun. I want the barrel 18” and as accurate as can be, as long as I do my part with match grade ammo.