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View Full Version : Gas block/free float conversion for DPMS.


toppermost
July 7, 2012, 10:20 PM
I want to replace my standard (mil-spec) drop-in handguard to a rifle length free float... My barrel has those grooves cut into it where the front sight base is pegged on.

Is there any reason I cannot extend the length of the gas tube - and bolt the new gas block further down the barrel? Would I have to drill and tap the barrel so that the new gas block would be secure?

Would the benefits be worth the trouble/cost? Or should I just put the new gas block where the old FSB was.

Marquezj16
July 7, 2012, 11:32 PM
Is there any reason I cannot extend the length of the gas tube - and bolt the new gas block further down the barrel? Would I have to drill and tap the barrel so that the new gas block would be secure?


This would prove difficult as you would have to drill another gas tube hole through your barrel while plugging the original one.

An easier work around would be to replace your front side base (FSB) with a low profile gas block that would fit under your rifle length free float tube.

BTW, if your FSB is pinned on to your barrel, it can be a pain to remove those pins. I've only been able to remove them using a front sight bench block from Brownells and some good hammer and punch work.

madcratebuilder
July 8, 2012, 07:51 AM
I want to replace my standard (mil-spec) drop-in handguard to a rifle length free float... My barrel has those grooves cut into it where the front sight base is pegged on.

Is there any reason I cannot extend the length of the gas tube - and bolt the new gas block further down the barrel? Would I have to drill and tap the barrel so that the new gas block would be secure?

Would the benefits be worth the trouble/cost? Or should I just put the new gas block where the old FSB was.

Changing gas port location is cost prohibitive. If you want a mid-length or rifle length gas system sell your current barrel and buy a new one in the length you want.

What you can do is cut the FSB down to a low profile size, or replace it with a new low profile that is secured with set screws. Install your rifle length hand guard over this. Then you can install a new FSB on the barrel in front of the new hand guard (no gas port needed) or use a front sight attached to the hand guard,

Is this what you want to end up with? 16" with rifle length guard?

http://i32.photobucket.com/albums/d37/madcratebuilder/AR15/july12build01.jpg

toppermost
July 8, 2012, 12:38 PM
Is this what you want to end up with? 16" with rifle length guard?
http://i32.photobucket.com/albums/d37/madcratebuilder/AR15/july12build01.jpg

Pretty much - just with a quad rail.

madcratebuilder
July 9, 2012, 07:39 AM
Pretty much - just with a quad rail.

OK, I would just cut down the FSB that's on your barrel. Hack saw and file or a Dremel tool. Touch up blue the raw metal. Now you have a low profile gas block that's pinned, about as heavy duty as it gets.

Choose a rifle or extended rifle length hand guard that mounts using the factory barrel nut. You well need to cut off the exsisting Delta ring and spring, Dremel tool strikes again.

Look for a FSB, a clamp on style, to mount in front of the new hand guard. I would cut the bayonet lug and sling mount off this for a smooth, snag free setup. It should look sort of like this, only closer to the end of the barrel.

http://i32.photobucket.com/albums/d37/madcratebuilder/AR15/fama203.jpg

Toxdoc
July 9, 2012, 10:32 AM
YHM makes a free float tube with a cut out for a pinned on front sight.

toppermost
July 9, 2012, 10:31 PM
Do they make many free float quad rails that screw onto mil spec receiver threads? Are they very stable?

edit: What I mean to say is: Can you explain a little more about cutting the delta ring off? I thought I would have to pretty much take the barrel off of the receiver and remove the mil-spec barrel nut??

How do you attach a free float quad rail to just that piece of hardware?
http://i226.photobucket.com/albums/dd271/toppermost/wha.png

madcratebuilder
July 10, 2012, 05:58 AM
How do you attach a free float quad rail to just that piece of hardware?

Floating guards that use the oem nut use a clam shell like adapter that clamps over the barrel nut and the guard attaches to this clam shell using screws.

This isn't the best photo for showing this but I think you can see how the clam shell fits over the barrel nut and the tube slides over the end of the clam shell.

http://i32.photobucket.com/albums/d37/madcratebuilder/AR15/apex03.jpg

If you can borrow a barrel nut wrench you well have a cleaner install if you remove the barrel and the gas block. Is the muzzle devise pinned? 14.5" barrel? By removing everything you can get the nose cap off. The muzzle devise needs to be removed to slide the FSB, nose cap and barrel nut from the barrel.

toppermost
July 11, 2012, 12:06 AM
I think I would feel more secure with a barrel nut with threads on both sides. I am leaning toward YHM.

But I am probably going to use my FSB as my gas block. According to DPMS all their barrels and FSB's are pinned by hand so they are all more or less unique. So if I grind it down I have an instant, custom-made low profile gas block.

Crow Hunter
July 11, 2012, 08:44 AM
You can also go with a Daniel Defense Omega rail.

All you have to do is take the old handguards off and put the Omega rail on and tighten some screws/set screws. I put one on my 6920 just last week.:D All I needed was my wife help to take off the handguards/add the rail sections while I held down the delta ring. (I think it would be easier with a delta ring tool)

No modification needed to the rifle, but you will only have a standard 7" handguard length rail. (I actually don't mind the shorter rail, I don't hold way out on the front and I like the lighter weight)

I think Centurion makes one that just requires cutting off the Delta ring and the spring.

Troy also makes their Alpha rail and I think Bravo rail, both of which are longer and extend out past the FSB but they also require cutting the delta ring and spring.

Depending on the design, some of them require a different barrel nut as well. It should say in the description.

Keep in mind, all the options are fairly expensive. The longer the rail, the more expensive it is.

The Omega runs about $250.

I did it because I wanted to lighten up the front end of my rifle. I did have a MI FSB mount, Surefire 6P & Vltor CK scout mount for a flashlight and the standard barrel mounted Colt sling swivel. It was very functional, but heavy (for me).

I did have to use a dremel cut of wheel to get the front sling swivel off. I couldn't get the pins to come out. I bent one punch and rounded the tip of another and the best I could do was get it flush.:mad: So cut it off and threw it in the garbage.:D

I switched to an DD Omega rail and added a Surefire X300. It is MUCH lighter and more lively and I can just take the light/sling off without affecting the rifle zero to make it even lighter for when I take it coyote hunting. It also lets me play around with other accesories without having to sight it back in when I move stuff around.

The X300 is also much less likely to have a light AD than the 6P. I can't cound the number of times that I have grabbed the rifle by the handguard to lift it out of the safe and blinded myself by hitting the light with the back of my hand.:o

toppermost
July 12, 2012, 06:15 PM
I am the proud new owner of a 12" Yankee Hill Machine free float quad rail. The "diamond one." It should get here Saturday! I picked up a Magpul front BUS and low profile gas block today.