Longer rail system

[scumhunter]

I have a new project in mind and I could use some expertise before I jump into it. I want to add an extended rail system to my M4. I currently have a MI 7” free float on my 16” barrel with the standard front post sight / gas block.
Can I just cut off the top of the sight and leave the pinned gas block as is or should I purchase a low profile after market gas block?
I had to cut off my delta ring to put on my current 7” MI free float rail system. My plan is to just get a longer MI rail so I know the transition won’t run into any snags. Do other companies like DD & Troy attach just like the MI free float? I’m happy with the MI but I would consider others if it isn’t going to cause me heartache.
I want to extend the rail system out as far as possible. With a free float system will it start to bend or bow, or move if I run it out to 12” or so? My 7” is rock solid but I’m just a little worried about having that much leverage out front.
I’ve pretty much settled on the Magpul MBUS but I’m open to other suggestions. The price and Magpul quality are my main reason for going this route. Honestly, the cool factor with the new MBUS may play into my tentative decision also.

[rob_s]

At one time I had a carbine with a 12.0 larue rail on a 14.5" LMT barrel. no flexion issues etc. I had Troy front and rear sights on it and had no trouble zeroing them at 50 yards like my Aimpoint.

I currently have a 16" barrel with an 11.0 DD rail and a 11.5" barrel with a DD 10.0 rail, both the M4 version and both with Troy front and rear sights, again with no flexion or zeroing issues.

I believe that the shaved FSB with stock pins is the best solution to the low profile gas block. Two taper pins are the strongest attachment you're going to find, and not having to drill two new holes in the barrel is a good thing. My 1.45" gun used a larue gas block, but my two current guns with rails are using the shaved FSB.

Generally speaking you have to dremel off a bit after cutting to get it to fit, but I'm not sure on how it works out with the MI rails. You're pretty much going to have to remove the FSB to grind it down anyway, so IMHO you'd be better off switching to a DD Lite of M4 rail as that's the only real impediment to installing these types of rails.

Some pics of the shaved FSB for you

[rob_s]

One other thing to keep in mind, is be sure of why you're doing what you're doing and be prepared to honestly evaluate what you've done. If you're not 100% positive that you'll like this setup, shaving the FSB is a permanent solution to some extent. Using a low-profile gas block allows you to mothball the stock FSB so you can change back to it later if you don't like the longer rail.

On my 14.5" gun I found the setup to be heavier than I'd like. In fairness that gun also had a Magpul M93B stock on it, but the overall setup was just too much for my tastes. Both of my current extended-rail guns have skinny .625" barrels on them which helps offset the added weight to some degree.

My initial reason for having the longer rails was to cover up the hot barrel when doing transitions or shooting from unconventional positions. I confess that when I built the first one "looks cool" was pretty high on my list of priorities too. I use DD M4 rails now because they were the lightest solution at the time I built the guns a couple of year ago.

You might find this chart with weights and sizes to be informative.

[scumhunter]

Generally speaking you have to dremel off a bit after cutting to get it to fit, but I'm not sure on how it works out with the MI rails. You're pretty much going to have to remove the FSB to grind it down anyway, so IMHO you'd be better off switching to a DD Lite of M4 rail as that's the only real impediment to installing these types of rails.
]

Wow, thanks for all the info and pics! So I shouldn't try to cut off and smooth out the FSB with it still on the barrel?

[gotm4]

Wow, thanks for all the info and pics! So I shouldn't try to cut off and smooth out the FSB with it still on the barrel?

You can do it that way and I've done that myself on a few barrels that had perm. mounted flash hiders. But it's better to completely remove the FSB. I'm now using a plasma cutter to remove the largest sections and then a die grinder and bench grinder to clean it up then sand blast and refinish with Norrells moly resin.

This Bushmaster FSB was shaved to fit under a Troy rail while still attached to the barrel.



This one was done off of the barrel. This is prior to refinish w/Norrells.



This one was a CMMG .625" thin barrel where I shaved the FSB small enough to fit under a 12" DD Omega rail. It was a 14.7" barrel with the A2 flash hider perm. mounted. Since the flash hider was never going to come off I ground the pins flush with the sides of the shaved FSB. An Omega rail is extremely narrow internally.

[Cameron]

I have had the same thing done on two rifles, a 16" Colt we cut off and "shaved" the front sight post by hand with a dremel, on the 10.5" LMT I sent it out to a gunsmith, as it was too much hard work for me...

I installed Daniel Defense Lite rails on each 12.0 and 10.0 respectively.

[scumhunter]

I’m planning on using a Dremel and maybe a bench grinder with caution. Is this going to be a monumental task or will it work fine with some patients and elbow grease? I’m hesitant to take the gas block off and reinstall it myself. I’m not a gunsmith; I don’t want to get in over my head and mess something up.

[Cameron]

You will be alright mate!

Just go slow and make sure you drink a little vodka or whiskey to steady your nerves.

It took about 2 hours to do the Colt barrel above with a hand held dremel...

[Policetacteam]

I'm scum's roommate so I don't think the whiskey part will be a problem!

[scumhunter]

I'm scum's roommate so I don't think the whiskey part will be a problem!

The whiskey barrel has been dry for some time now. I may have to dip into some of your skunky beer to steady my hand. I see you have stumbled across my new project here; I may need some assistance with it. Can you pencil in some gunsmith time or do I need to contact your secretary? Better yet, I’ll just have her help me. Her attention to detail could come in handy.

[scumhunter]

I have had the same thing done on two rifles, a 16" Colt we cut off and "shaved" the front sight post by hand with a dremel, on the 10.5" LMT I sent it out to a gunsmith, as it was too much hard work for me...

I installed Daniel Defense Lite rails on each 12.0 and 10.0 respectively.

Great pics. This is exactly what I'm going for.