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Discussion Starter #1 (Edited)
Making Super Lite AR 308 Hand guard, this also works for AR 15 Hand Guards. You don't have to epoxy the AR15 DPMS and Clark Custom carbon fiber hand guards direct to the aluminum barrel nuts.

Less than 5 ounces, or 3-4 ounces lighter than any other AR 308 hand guard.

I am using the DPMS 308 aluminum barrel nut and AR 308 carbon fiber hand guard tube. This tube is almost three times as thick as the cheaper AR 15 carbon fiber tubes.
My secret is I combine a lighter 9.5 inch AR 15 carbon fiber tube and interference fit into two inches of the thicker DPMS AR 308 tube. The thicker section stiffens the hand guard and works great for threading into the barrel nut.
I want my hand-guard to just cover the gas block, so total length must be close to 10 to 10.3 inches.
The DMPS barrel nut weighs 1.7 ounces and is 1.5 inches thick.


I will be tapping three M4x6 titanium button head screws through the carbon fiber and into the thicker part of the barrel nut, the section with no threads. I am using M4 button head allen screws because it is impossible to get button head titanium in 6/32 or 8/32 inch threads.

The thicker barrel nut section with no threads; is one half inch deep. So I first drill one hole into the carbon fiber @ 1.25 inches from the threaded end, centering in the thicker aluminum section of the barrel nut when I finally drill a hole into the nut. Then I drill two more holes into the carbon fiber at 90 degrees to the bottom hole.
After tightening the barrel nut onto the receiver (with ant-seize) three times at full torque, I can establish the exact bottom of the barrel nut, centered between the front pin section on the bottom of the receiver.


I can take the barrel nut off and drill three holes 0.6 mm in depth, or just touching the bottom of each hole in the barrel nut. I will then tap the barrel nut for the M4 titanium screws. Depending on how the threaded holes feel, I can leave alone or put some JB Weld or aluminum to strengthen the tapped holes.

The inner diameter of the 2 inch section of heavy DPMS carbon fiber tube is 1.936 inches. The OD of AP Custom AR 15 carbon fiber is 2.00 inches, while the cheaper CTS and eBay tubing OD is 1.990 inches. I am using the cheaper and thinner eBay carbon fiber tubing @ 9.5 inches length. Total hand guard length is 11 inches.


Any bonding of carbon fiber has to include complete removal of the mold release agent and the shiny gloss surface of the tubes. So I sand the OD of the AR 15 tube about one half inch, and the ID of the AR 308 tube again a little more than one half inch. Here is the AR15 tube with the mold release agent removed.


Here is the inside of the 308 tube with the AR15 tube pressed into it. You can see the areas I removed the release agent in preparation for gluing.




Here is the inside where I am adding the epoxy, still a small section to finish up.


Here is just the AR308 CF portion held on to the barrel nut with 3 titanium button head screws


I use carbon fiber glue (Devcon 2 Ton Epoxy) and press the AR 15 tube into the AR 308 tube. You have to be careful to center the AR15 tube around the barrel. Once centered I let the epoxy dry for 12-18 hours.

Total weight of the hand guard is between 4.5 and 5.0 ounces.


Total weigh of this hand guard is 5.0 ounces with screws. Barrel nut is 1.70 and the CF with 3 titanium is 3.30 ounces.


<O:p</O:p
Note carbon fiber is NASTY. I use an old vacuum cleaner, rubber gloves, professional dust mask and goggles.
<O:p</O:p
 

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Butt ugly.....Why not just use nomex gloves and skip the handguard, you could save more weight as the glove wouldn't count on your tally sheet??????
 

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Discussion Starter #5
JTallen83 comes from the AR308 forum where there is really zero exchange of information, just a bunch of bad apples. Lots of stupid inane commenters over there.

We are so lucky we have so many people who contribute to the best AR forum, the 68forums. Another one to stay away from the 6.5 grumble forum.
 

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Discussion Starter #6 (Edited)
Next project is to get another Clark Custom 308 aluminum barrel nut. By cutting half an inch from it's width and using super thin carbon fiber tubing, I figure I can make a 10.5 inch hand guard about 3.3 ounces total. That's 1.7 ounces off the upper. I am at 87 ounces right now, my goal was 83.2 ounces or 5.2 pounds. Working on getting a lighter gas block and a lighter pistol grip for another 0.6 ounces.



 

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Discussion Starter #8
I use 24 teeth hacksaw, using an old vacuum that has a HEPA air filter. I fine tune the CF with 60 grit sandpaper.

I use gloves that I throw away, safety face goggles and a half face mask that filters down below one micron.

Have 3 dremils, they just spread too much BAD carbon fiber dust. Used to use 32 tooth hacksaw blades, dull too fast and took too long.

I use 2 Ton Devcon epoxy to glue.

Here is a sampling of AR15 and AR 308 carbon fiber tubes I have:
 

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Discussion Starter #10
Safety gear

You can get particulate face masks, this one is first rate. Some goggles have holes in the rim, notice these do not let any fine CF in against the eyes.

I also always use blue painters tape where I cut, holds the particles down.

Any one else have some safety tips??? I know there are more people here working with carbon fiber.

 

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Is it possible to cut it wet? Using running water like a ceramic tile saw? I stripped wax off asbestos floor tile almost 20 years ago using a wet solution and as long as it was wet we could do/use almost anything we wanted.
 

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They do seem to recommend wet saws from my reading so it looks like a tile saw would be a worthwhile investment if doing a lot of tubes or if you are going to retile a bathroom or two. LOL

http://www.carbonfibertubeshop.com/cut & bond.html
...or as extravagant as an industrial wet saw costing thousands of dollars

http://www.acpsales.com/Cutting-Composite-Tubes-and-Rods.html
Cutting with a Tile Saw with a Toothless Carbide Blade

A tile saw is an ideal tool for cutting multiple rods and tubes or thicker materials. A wet saw lessens the amount of dust produced and when used with a toothless carbide blade cuts though the material quickly and minimalizes splintering.
 

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Discussion Starter #14
Got my Clark Custom 308 aluminum barrel nut today. Weighed at 2.10 ounces. Clark claims to have the lightest barrel nut, but they ignore the DPMS that is 1.70 ounces.

I am going with the Clark Custom as it has a more "normal" OD of 2.00 inches. There are a ton of carbon fiber tubes with 2.00 ID's.

But the Clark has an inch of aluminum that contains the extension, so I cut one quarter inch and new weight is 1.60 ounces.

This is the cut side, needs to be made flatter.


This is the threaded side:


Compare this to the photo at post #6 of this thread:



Next to come is the ultra thin carbon fiber, 10.5 inches are 1.62 ounces, total 3.2 ounces. that cuts 1.8 ounces off the upper.
 

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Discussion Starter #15 (Edited)
Got the carbon fiber for the new AR 308 hand guard, with barrel nut total weight 2.95 ounces. Very thin but I don't use the hand guard when I shoot, I pull back with the left hand on the mag well.

At 10.5 inches it will cover the gas block.



 

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Discussion Starter #16
Lots of people in several forums were asking me how I made the super lite AR 308 hand guard under 3 ounces total so bringing this thread back.

I am trying to get my AR15 hand guard under 4 ounce, have to find either smaller diameter CF tubing or thinner tubing.
 
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