Geissele Mk1 "10 inch" Rail Owners....need your help.

**luckydube56** · 03-12-13, 00:41

First off, Bill Geissele makes the best looking rail, IMHO, on the market. The man has an eye for aesthetics.

My question:

What is the actual length of the Mk1 SMR(M4) 10inch Rail? I'm looking to build an SBR but I want a rail that will go just up to the edge of a flash hider....an AAC 51T Brake to be exact. At 10 inches, I believe it would be too long for a 10.5 inch barrel when accounting for the .625 length of thread. An 11.5 inch barrel would expose a little more barrel than I would prefer but still functional.

The reason I ask is that I've seen their HK416 Rail listed as a 10.5 inch rail. That would not be possible since the the SBR version of this rifle has a 10.4 inch barrel and the pics show the flash hider clears the rail.

I've searched this forum, others like it, and have basically gone to the end of the internet. Nothing.

**MountainRaven** · 03-12-13, 01:00

Including the overlap with the receiver, it is 10.25 inches.

And right at 10 inches to the receiver.

**luckydube56** · 03-12-13, 01:07

Well that was quick. Thanks Fjallhrafn. 11.5 it is.

**horseman234** · 03-12-13, 08:42

Here's a crappy cell phone pic of a 10.5 Rainier 300blk barrel with a 10" geissele mk1 rail, and a Yankee Hill Phantom QD. As you can see the QD FH collar just clears the rail.

http://s1326.beta.photobucket.com/us...047cf.jpg.html

**luckydube56** · 03-12-13, 15:25

Originally Posted by horseman234

Here's a crappy cell phone pic of a 10.5 Rainier 300blk barrel with a 10" geissele mk1 rail, and a Yankee Hill Phantom QD. As you can see the QD FH collar just clears the rail.

http://s1326.beta.photobucket.com/us...047cf.jpg.html

Well that's interesting. I didnt think it would clear. How long is the threaded end of the barrel on a 300 blk? Seems it must be shorter than the ~.6 - .625 inches of a AR15 barrel. Nice rifle!!

**horseman234** · 03-12-13, 17:07

It's .625 as well. On the Yankee Hill, and I THINK on the AAC, there is a narrower piece of the FH which sits behind the wider collar. That piece partly fits inside the rail, but does not affect the attachment. If you have the AAC, or know someone who does, measure it. From the pictures, I think it would clear.

**luckydube56** · 03-12-13, 20:58

Originally Posted by horseman234

It's .625 as well. On the Yankee Hill, and I THINK on the AAC, there is a narrower piece of the FH which sits behind the wider collar. That piece partly fits inside the rail, but does not affect the attachment. If you have the AAC, or know someone who does, measure it. From the pictures, I think it would clear.

Thanks horseman.

I believe what you're referring to is the wrench flat portion behind the flash hider. And it sounds like you're saying at least a portion of the wrench flat will recess into the rail.

The problem with the AAC Flash hider is that I've heard or read somewhere the wrench flat portion is not threaded and is actually designed to slide over the barrel's outer diameter and past the threading. Which means the FH's wide collar will sit in the same location as if it had no wrench flat behind it.

I appreciate your help. It sounds silly to some that my decision on the barrel length is based around a rail and purely cosmetic but what can I say? It's a nice rail.

**Adam Pini** · 03-12-13, 21:08

I installed a 10" SMR on one of my LMT 10.5s. It works but it will overlap the shoulder of the treads. I run a SF can and had to order a MB556k-pn from BCM to make it work.

The SMR is the most solid rail ive ever used. I feel like i could beat people to death with it alone. Rock solid lock up and ergonomic

10.5 upper with 10" Geissele SMR

Space that the MB556k-pn give me on this option

Overlap of the rail

Out in the wild

**luckydube56** · 03-12-13, 21:55

You guys are making me drool.

It looks like the overlap is around 1/8inch which I kind of envisioned.

So it's definitely possible to use a 10.5 barrel; just not with the AAC unless I use a crap load of spacers.