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Discussion Starter #1
I'm putting my first 6.8mm rifle together and bought a blemished DPMS Carbon Fiber free float tube from Brownells to finish the build (arctic color I'll fix that later...). I wanted something non-metal because metal forends get very cold and I'm planning to use this as my hunting rifle this year. These types of tube are light and inexpensive (especially the blemished version) but usually require gluing the tube to the aluminum barrel nut with epoxy. This works well and is strong, but I wanted a way to remove the tube and dry the barrel off as everything gets soaked during west side deer hunting in Washington State.

I've seen some threads about adding screws hold the CF tube to the barrel nut and this seemed like the best method. I decided to add steel bushing to protect the carbon fiber and thread the barrel nut in front of the barrel threads to accept the screws.

The upper is a standard 16 inch CMMG 6.8 SPC II upper with m4 barrel contour and a standard carbine length gas system and front sight/gas block. The first thing I did was fire 20 rounds through it to ensure the upper functioned properly. Everything worked as expected and the brass looked good so I decided to cut down the front sight rather than use a low profile gas block.

Everything taken apart:




Tube marked and three holes drilled for the screws:



To make the bushings I used some large steel pop rivets but you could use anything to get a similar effect:



Test fit:
 

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Discussion Starter #2
Barrel nut drilled and tapped:




Ready for test fit:




Screws are too long...




Screws trimmed to fit:







Test fit:

 

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Discussion Starter #3
Test fit on upper:




Turns out, the camo comes off with alcohol:




I decided to use JB weld so it would stick well to the steel bushings:




Bushings JB welded in place:




Cheap flat black paint, I may use some kind of heat shrink tubing in the future...




Finished, ready for accuracy testing with a Palmetto lower and Zeiss Conquest 4.5-14x50:

 

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I like where that's headed. The rivets as a bushing are a good idea too. Keep the tale/pix coming. Will enjoy following this project. :a04:
 

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Discussion Starter #5
I like where that's headed. The rivets as a bushing are a good idea too. Keep the tale/pix coming. Will enjoy following this project. :a04:

I'll report back when I get a chance to shoot for groups. It's worth noting that the tube is very solid because it fits tightly against a ridge at the back of the barrel nut and the screws hold it in place.

Also, the tube itself is a tight fit on the barrel nut, it take a minute to work it off. I don't think this setup would work if you were going to take the tube on and off a lot as the carbon fiber would eventually wear down (and the tube could get loose) but it should be find for taking it off once or twice a season.
 

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Agreed. I used one of those when I built my 6.8 pistol. Instead of gluing it up, I opted to swap over to an AP Customs CF Tube. The DPMS unit found another home.
 

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Very good example of innovating instead of imitating. Looking forward to your range report and finished product.
 

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Excellent solution. A buddy and I tried unsuccessfully to get an epoxied handguard off so he could add a mount for his bipod - frustrating!
 

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I had to laugh when I saw that same 13 inch DPMS hand guard I bought earlier this month.

I have several carbon fiber hand guards, what I have been doing lately is drill a small hole either 3 or 4 around the circumference of the carbon fiber hand guard.

Once the barrel nut is on, I position the tube so one of the holes is in the bottom, then drill and tap that hole. I do not go all the way through the barrel nut like you did.

I am using M4 titanium button head screws, you can't get 6/32 or 8/32 in titanium button head.

Once I am happy with it, I than remove everything and fill the 4 holes with JB Weld ( or aluminum epoxy), and then stick a paper stick in the hole and let it solidify. The I drill out the hole again and tap again. Now there is some strength on the side of the screws and every thing is tighter.

Only done one exactly like this, next one I will take photos.

Thanks for the great tips, I don't really like the camo either. But it was cheap and it works great.
 

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great idea. I just bought 2 from Brownells, gonna give it a try. Thanks for the ideas
 

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Discussion Starter #16
I added some 50mm heat shrink tubing I bought off eBay for $7. I wanted something to make the carbon fiber "ring" less when you tapped on it and give it a rubber feel.

Heat shrink tubing next to the tube:


Small test ring:


I decided to leave the ring in place, why not?


Heat gun:


Finished:
 

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Discussion Starter #17
Rifle in the field, this is why I wanted the tube to be removable. Everything needs to be dried off after hunting in Washington!

 

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Borrowed your idea and added a QD
attachment from Magpul



Cut the hand guard down to 10" and now I have a 5.5 lbs AR without optics and has great balance
 

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I have an LMT 10½ and just never did get to attaching that tube. In hindsight, no heat escapes and it's a poor design IMHO.

When I get around to taking off the barrel nut, I'll sell it.

Thought about drilling some air holes but carbon dust is heap bad medicine.

What are they selling for?
 
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