CMR sold out everywhere?

**GOST** · 31 January 2014, 19:26

What's it going on?

**LMMzach** · 31 January 2014, 21:22

16" rainier build. Will post in explain ar thread when finished

**LMMzach** · 1 February 2014, 19:52

Got an email today from stonefire saying my rail shipped. They seem to be on top of things.

**mustangfreek** · 2 February 2014, 02:41

Originally Posted by LMMzach

Got an email today from stonefire saying my rail shipped. They seem to be on top of things.

Ya dwayne and his wife are really nice people and always shipped fast when i ordered thru them..

**LMMzach** · 8 February 2014, 18:08

Got my cmr thing is sick!

but I ran into this

The rail fits over the gas block but once bolted it touches the bottom of it is that going to be an issue? There is plenty of room on the top side. It is a fortis low pro

**GOST** · 9 February 2014, 03:57

I'd heard that some lo pro GB's wouldn't work with rail, but never had seen it it till now. I honestly don't know if this is an issue, it'll take one smarter than I to answer this.

**Slippers** · 9 February 2014, 06:16

There's a lengthy cmr info thread on m4c where it gets mentioned more than a few times. Only the centurion gas block and a shaved fsb clear without problems, although I did recently see a user who had problems with the set screw sticking out too far on his centurion gas block because his barrel wasn't dimpled. Some people get away with various other gas blocks but it's hit and miss, no consistency to it.

General consensus is to file/grind the bottom of the gas block a little so you get at least a 10th of an inch clearance.

**UWone77** · 9 February 2014, 13:45

What kind of barrel are you using?

I've got 2 lo-pro's installed on CMR's, but don't have this issue. I'll have to double check which lo-pro's and barrels I'm using.

**LMMzach** · 9 February 2014, 16:44

It is a rainier arms mountain series 16"

**Slippers** · 10 February 2014, 11:27

Just to follow up regarding gas blocks and fitment issues:

Assuming your barrel is perfectly centered in the rail, a 0.750" diameter barrel at the gas block will leave 0.1850" of clearance between the bottom of the barrel and the inside of the CMR.

A 0.625" diameter barrel at the gas block will leave 0.2475" of clearance between the bottom of the barrel and the inside of the CMR.

You can then measure the thickness of the bottom of various gas blocks and get a general idea of whether they will work or not.

Mike at ROG was nice enough to measure a few 0.750" gas blocks at the bottom and had these measurements:

YHM: 0.186" (I measured this one)
Noveske: 0.187"
Diamondhead: 0.185"
BCM: 0.186"
Vltor (set-screw): 0.187"
Geissele: 0.265

Anything around 0.185" *might* work if you get lucky and your barrel sits a little high inside the CMR. Of course, any slight pressure on the handguard might cause it to contact the gas block...

Here are some actual experiences from end users:

YHM low pro doesn't fit without grinding: http://www.m4carbine.net/showthread....66#post1802666

Noveske low pro needs to be grinded as well: http://www.m4carbine.net/showthread....90#post1795390

Parallax low profile gas block seems to have a sliver of clearance, but any flex of the rail means it'll probably hit: http://www.m4carbine.net/showthread....49#post1687749

Sadlak .625 gas block works fine: http://www.m4carbine.net/showthread....68#post1680268

Geissele gas block hits the bottom: http://www.m4carbine.net/showthread....32#post1672232

Vltor gas block hits the bottom: http://www.m4carbine.net/showthread....29#post1661229

Rainier Arms gas block hits the bottom: http://www.m4carbine.net/showthread....97#post1668297

Black River Tactical micro pin gas block has a tiny bit of clearance, but you should still probably grind it down: http://www.m4carbine.net/showthread....02#post1841202

Stickman mentions a few times in the M4C thread that his BCM gas blocks work, but have very little clearance.

**LMMzach** · 10 February 2014, 13:09

Great response thank you. I have a friend with the proper tools to grind a nice flat edge on my gas block.

I don't want it touching personally. But what is the problem with it touching? Just noise or will it affect the shooting of the rifle since I guess it's not technically free float then

**Slippers** · 10 February 2014, 14:05

Originally Posted by LMMzach

I don't want it touching personally. But what is the problem with it touching? Just noise or will it affect the shooting of the rifle since I guess it's not technically free float then

Exactly, it won't be free floated any longer if it's touching. Even if it's really close you risk having the handguard hit it if you flex it at all, such as if you sling up to pull the rifle in tight. Anything touching the barrel/gas block in an inconsistent manner will change your point of impact at distance.

**LMMzach** · 12 February 2014, 11:23

Little update for anyone who cares. I got a buddy to mill down my fortis block for me did an amazing job. Had to cut the bolts tho I'm not really thrilled about that part but we will see how it works. Here's a couple I phone shots there is a lot of room in there now

**GOST** · 13 February 2014, 04:20

Very nice, I will be needing pics of the whole rifle.

**UWone77** · 13 February 2014, 14:37

I finally checked my CMR with the Fortis gas block. Much like LMMzach's picture, mine is also touching the rail. I haven't noticed any issues when shooting it, and didn't even think to check until I saw this thread.

I went ahead and took the rail off to see if there was any "rubbing" between the gas block and rail, but I could not locate any obvious wear marks. The rail slides on and off without issue.

This doesn't seem to be an issue with a .308 CMR/barrel/gas block.

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