Well, there is two ways to go about it. It should be noted that I have NOT done this myself. I've just seen the results of others.
SAFETY WARNING: Carbon fiber dust is NASTY STUFF. Work in a ventilated area. Wear a mask. Do NOT breathe the dust in! Consider wetting the work area to control the dust or have a partner stand near you with a vacuum cleaner wand turned on.
MECHANICAL WARNING: Carbon fiber can fray, so be sure to use a NEW drill bit, or a recently sharpened drill bit.
1) The Magpul MOE rails have a flat bottom. They come with screws and a backplates. Put some masking tape on the forend. This makes it easier to see the marks you're going to made. Next, you'll need to place the rail at the desired positions, then mark the screw holes. Drill out the holes, then screw on the picatinny rail.
Remember, the bottom of the rails are flat, so they won't sit flush to your round forend. That's generally not a problem for side rails, as you'll be attaching lightweight accessories. Some have taken the rails and put them on a drum sander and contoured the bottoms to match the forend. Others filled in the gap with epoxy. This is good if it's going to be a permanent install. Both ways are pretty cheap. The bottom rail needs to be stronger, as you will be attaching a bipod (eventually). You're going to want to epoxy the bottom one, for sure.
Epoxy method
Go to a Target Pharmacy and ask for four to six oral syringes. If they are feeling generous, they'll just give them to you. If not, they're for sale on the shelves for about $3.00.
Follow the previous instructions for installing the rails, but when it comes to wrapping the forend with masking tape, tape up a larger area. This will also be your work area for the epoxy. Also, place some oil on the screws and backplates, so the epoxy won't bond to the hardware.
Once the rails are installed, mix your epoxy solution and dump it into the oral syringe. Make enough to fill 1/2 of the syringe. Using the syringe, fill in the back of the rail to build the contour. If the epoxy is thick and doesn't run, then you can do all of the rails at the same time. If it's runny, then plan accordingly. You may have to do one side of each rail, let dry, then do the other side, let dry, then do the bottom rail.
After the epoxy has cured, remove the rails from the forend. Remove the tape from the forend. Trim off the tape that is bonded with the rail. Use a utility knife or a dremel to clean up any epoxy that may have run or was over-filled. Clean off oil on the screws and backplates. During re-installation, use some lock-tite blue on the threads. Done!
2)
Alternatively, you can buy the actual PRI rails. This would be my first choice. The back of the rails are curved to match a 2" Outside Diameter round forend. They come with the hardware to install to your forend and there isn't much you need to do except decide where you want to put them, mark holes, drill and install. Of course, this convenience comes with a slightly higher price tag. Not bad, though. It's $18.00 for the
3" rail, $25 for the
5" rail, and $35 for the
8.5" rail.
You'll just need to contact DPMS and see if their forend has an Outside Diameter of 2" (or close to it).
Most people just add a 3" rail to the sides and the bottom. At $18 each, it's only $54.00 in addition to the $100 cost of the DPMS carbon fiber forend. The top rail is useless unless you think you're going to be adding a night vision scope in front of your rifle scope or you want to add a BUIS to the final build.
Note: When utilizing the new forend, you're going to need to replace the gas block with a low profile one, as the forend extends past the gas block. You can buy one, or I have a guy that can take your existing one and mill down the profile.
