Essentially what I want to build is something that looks similiar to a Dissipator.
I want to take a 14.5 LMT upper, remove the FSB, add a rifle length FF rail system and then hide the gas block under the FF rail system and put a folding front site at the edge of the FF rail.
What make/model FF and gas block should I use?
Would this work and what would it look like. If you have pictures of this type of setup please show me and describe how you did it.
Thanks for you help.
Yes, it will work. It is a very popular configuration.
Here are some pics of various variations . .
10" Mi FF over a 16" M4 carbine
10" DD over a 11.5"
10" DD over a 11.5"
12" Troy over a 14.5" M4
12" YHM over a 16" Hbar
Wow, Thanks Bravo Company.
What Gas Block would work under the MI FF?
Troy, PRI, Vltor, Larue would all work well.
You could just cut and grind your FSB. I did my 16" like that, tr=hrew a YHM FF forearm on it and I love it!
Top gun is as you describe.
As for gas blocks, if you use a Larue rail you’ll have to use their gas block. If you use Daniel Defense you can simply grind down your FSB until it fits under the forend.
Another view of the same rifle where you can see the Larue gas block under the Larue rail.
This was an LMT 14.5" complete M4 upper with Gemtech Bilock flash suppressor permanently attached by Gemtech.
Thanks Rob_s.
Those are exactly what I want to do. I’ll use those pics nightly as drool material.
My build is as follows.
DoubleStar lower Purchased
CMT LPK Pending
Magpul CTR Purchased
Magpul Miad Pending
LMT M4 upper Purchased
Larue 12 inch forend Pending
Dieter VFG or TD VFG Pending
Arms 40L Pending
FS ??? Pending
Am I missing anything? Any recommendations or anyhting I should change.
Most any GB would fit under the MI.
MI, YHM, PRI, Troy, Vltor
im looking to do something similar…
i have a stock lmt carbine gas ar15 that i use as a patrol rifle. i would like to make it a mid length gas system, but keep the fsb near the muzzle to have the extended range for my buis. i am thinking of having a low profile gas block installed and having an fsb installed near the muzzle, but what type of barrel would i need to accomadate the fsb? does anyone make a barrel like that that isnt a heavy profile? i would like to keep the weight at a minimum if possible.
thanks…
It’s possible to use a shaved FSB under a LT rail, but it takes an LOT of grinding. And possibly, some reverse order of operations on the assembly. I wasn’t comfortable grinding the taper pin holes any further, so I put the rail in place, left it loose, and then inserted the gas block/tube assembly in and pinned it in place through the holes in the rail. I’ve since seen gas blocks that were ground further and look like they’d fit through the hole on the Larue rail. The hole at the back of the LT rail is exactly the shape/size of their gas block.
Here’s the rifle I did it on (12" rail on 16" barrel):
(click)
Edited to add…It was a colossal pain to get it ground down enough, I’m pleased with the result but I’d probably do the LT gas block if I had to do it over again. It’s nice having a pinned block but with it protected by the rail, non-pinned wouldn’t worry me too much.
I’m not sure a standard FSB would accommodate what you are trying to do in terms of elevation adjustment, you may have to find a new post. If you want a longer sight radius and a FSB, you might want to look at dissy style barrels. If you aren’t absolutely set in stone regarding the FSB, something like what you see in this thread, with the rifle length rail and clamp on front BUIS is about as long as you’re going to get in terms of sight radius unless you can find a 14" rail. Be advised that a rail that long makes for a gun that is a little front heavy and awkward, but you’ll probably never burn your hand on the barrel 
Do you really need your BUIS to be that accurate on a patrol rifle? Really though, if weight is a concern, what has been shown in this thread is about as good as it gets unless you start looking at options like the VTAC 12" FF tube.