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Posted: 8/13/2011 9:18:08 AM EDT
Would like to cut down the forward sight to make room for a longer free float handguard to go on my M4 carbine to replace the plastic round version. Any suggestions as to which length would be most functional? I will likely be using a medium lenght scope on this weapon at some point but like having the handguard longer for the way I prefer to grip the weapon.
I was considering the mid-length. I have never replaced handguards and like the idea of freefloat but if it is rediculously difficult without specialty tools, I could install a two piece version. I would like to have the front of the handguard covered just because I do not like the open look.
If I use a dremel to remove the front sight tower, will the remaining gas block be low enough to allow the handguard to fit over it? I cannot see any advantage of completely removing the front sight just to install another gas block.
Any ideas, tips, or warnings based on experience are welcome and appreciated.

Thanks to all.

eseaton
Link Posted: 8/13/2011 10:07:36 AM EDT
OP:
Dremeling down a FSB to make a low profile gas block is a great idea. It is already pinned in the position it needs to be in and pins are the best method of holding it in place.

It will be low enough but you've got to profile the sides of the gas block to be skinny enough to fit inside the toprail of your chosen free float.

When choosing a FF handguard you'll want the kind that fits your hands best and has the length you want.

The Troy TRXs are very popular here and for good reason: inexpensive, quality, and lightweight. I have a TRX Vtac on every AR upper I have now.

When doing a FF forearm install you'll need to have a bench vise and upper receiver mounting block, torque wrench, a set of pin punches, hammer, moly grease, and a wrench to remove the muzzle device.

First, twist the muzzle device off. Take the plastic handguards off. With muzzle facing left tap the 2 FSB pins out. Slide it off the barrel leaving the gas tube intact.

This is where you cut the top off leaving the gas block portion. Also remove the bayo-lug and sling swivel via punch or cutoff wheel. You'll want to make the gas block area into a teardrop shape by grinding wheel on a dremel.

Profile it until it fits inside the chosen forearm.

While this is still off you'll either remove the delta pack by cutting, disassembling the entire barrel nut and delta assembly, or install something like a Daniel Defense Omega 9 handguard which will over the gas block completely. If the chosen handguard does not use a factory barrel nut but supplies its own you will have extra parts to build another gun into...

When installing a new barrel nut you'll want to grease the threads with moly grease and torque to the manufacturers specifications. This is where the torque wrench is necessary. Also make sure the receiver is installed in a proper mounting block. PRI, Spikes, Panther Claw, Clamshell all work on standard uppers. The PRI is best imho since it also mounts uppers by picatinny rail for perfect alignment when doing FF installs so that everything is same plane.

After you've put the new barrel nut on to spec, make sure the gas tube can slide through and pin the gas block back in place. Muzzle faces right, large side of pins facing up. If they're not taper pins any direction will do.

Reinstall your muzzle device with a new crush washer unless it is a brake and needs timing with peel washers.

Put the new forearm on. Go rezero your optics. Enjoy.

Any questions?
Link Posted: 8/13/2011 11:39:25 AM EDT
[Last Edit: 8/13/2011 11:41:51 AM EDT by Herknav90]
Pretty good advise above. I would remove the two pins on the FSB and remove the entire barrel nut assembly. Store it in a tupperware container or something.

Also, look at the YHM Specter length. It's designed to fully cover the gas block for a carbine - 9" instead of 7". Also, you will have to paint or coat the FSB when done. I actually used BBQ paint good for 1500 degrees. There will be some peopel to chime in the other paints and coatings.

Link

My carbine. I have put a reddot on the thing, and also the YHM end cap. I'm not too sold on the end cap.

Link Posted: 8/13/2011 2:27:45 PM EDT
[Last Edit: 8/13/2011 2:32:15 PM EDT by LMTRocks]
I had a Specter (9.6") on my 10.5" and it covered the chopped FSB with room for the end cap. My 9" Troy Vtac is now on that gun and comes flush with the end of the low-profiled FSB.

Link Posted: 8/13/2011 4:40:33 PM EDT
OP, here's a pretty good vid showing how to cut down the FSB.

http://www.youtube.com/watch?v=I5rPPyYdFUs
Link Posted: 8/13/2011 6:11:38 PM EDT
Video

#1 Would not clamp the part that goes around the barrel in a vise like that - You may find it won't fit around the barrel. Clamp the stuff that you are going to grind off anyway.

#2 Wouldn't use the grinding wheel. Gets too hot, and the way he has it clamped, it defiantely would heat it up so that the barrel part to go out of round with the vise clamping. Hack saw slower, and heat transfer not as bad.

#3 Use a pedastel grinder with 80 grit and 200 grit wheel - dip in water to keep cool. Clean up with the dremel with 400 grit. BBQ paint or the stuff he used matches pretty good.

DONE!
Link Posted: 8/13/2011 6:53:24 PM EDT
Does anyone have experience with Spike's BAR/SAR Rails with a chopped FSB? I am really liking their forearms but I have yet to hear of someone using one with a cut down FSB. Thanks!
Link Posted: 8/13/2011 9:26:57 PM EDT

Originally Posted By Herknav90:
Video

#1 Would not clamp the part that goes around the barrel in a vise like that - You may find it won't fit around the barrel. Clamp the stuff that you are going to grind off anyway.

#2 Wouldn't use the grinding wheel. Gets too hot, and the way he has it clamped, it defiantely would heat it up so that the barrel part to go out of round with the vise clamping. Hack saw slower, and heat transfer not as bad.

#3 Use a pedastel grinder with 80 grit and 200 grit wheel - dip in water to keep cool. Clean up with the dremel with 400 grit. BBQ paint or the stuff he used matches pretty good.

DONE!

None of those things have happened to the ones I've done. It's a pretty robust part and it's made to handle plenty of heat being a gas block and all.
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