Keltec CMR-30 extended handguard rebuild!

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  • jdindadell

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    267   0   1
    Feb 14, 2010
    4,200
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    Slidell
    A little back story here, I recently traded into a CMR-30 from another member.

    The original owner (to my best knowledge) and not the guy I rtraded with, had purchased, fabb-ed and installed an extended handguard.

    He/She purchased the following parts, likely from Keltec. Number refer to the exploded diagram from Keltec on their site. Not sure I fi can link that or not but it is an easy find.

    420 top chassis
    321 bottom chassis
    440 x2 bottom chassis rail section
    102 x2 barrel block

    So he/she cut the upper chassis to length, which is dictated by having to work around the existing cocking handle slots.

    then cut the bottom chassis "roughly" to length

    and then cut the 2 rail sections "roughly" to length.

    Used the left over pieces of the rail section to mount the 2 barrel clocks together at the sides where the new rail section assembly met the existing rail assembly of the CMR. So only 2 screws on each side held the new extension to the existing rail assembly. And a single screw was installed at the top, but the hole was drilled wildly out of square and missed the barrel block almost entirely.

    So the assembly was not really strong enough, especially if you added a vert grip to this section.

    So I took it all apart and figured out a a new way to use these parts.

    Here are a few pics of the parts, I have done some work on them, so these are not exactly as I received them. Note the hole drilled in the top rail, it was done at an angle, and almost completely missed the bock. Awful work.



     
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    jdindadell

    Not Banned!!!
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    267   0   1
    Feb 14, 2010
    4,200
    63
    Slidell
    So, the first thing I did was mate 2 of the barrel blocks together. I did this by clamping them together (perfectly aligned on all 4 sides), then drilling an undersize hole through both. I tapped a 1/4-20 thread on the gun side block, and enlarged the hole on the extension side block to match the diameter of the thread of the allen bolt. I did this so that there was minimal slack but only one block was threaded so they could be clamped tightly together.




    After that was complete and I had both blocks clamped together perfectly with the bolt, I drilled a small hole through both blocks to insert a pin. This pin will act as an anti-rotation device.



    Once I had the blocks properly mated, I installed them back on the front of the gun and started to dress the rough end of the handguard extension. When the chassis pieces were originally cut, they were not cut to the same length, and certainly not cleaned up at all.

    I did this with a bastard file, taking care to make sure all of the surfaces were true to each other and square as an assembly. The lower rail section was already too short, nothing I could really do about that. Originally this was installed as the top rail section, and it looked awful, like something had chewed on it. I swapped it to the bottom, and it looks ok. Just happens to be covered with the back edge of the Magpul RVG that I put on, pure luck it landed in this location. I could buy another rail section, and cut it to the correct length, but I am trying to salvage as many parts as I can.

    As the sections of the upper chassis were cut out of the middle of an existing complete upper chassis, it lacked holes in the correct locations. Some were very close, so I enlarged them with a needle file for optimum fit. The rail sections mount to the chassis with screws from the inside, and since 2 of the bottom rails are used here, the mount holes did not line up with the top chassis. The bottom chassis had just been shortened, so those holes lined up just fine.

    Last thing to do was to drill holes in the rail sections and the chassis pieces at the end to accept the screws that hold said pieces to the barrel block. Had to mill slots to match the factory ends, figured it would look better.

    I will coat the silver areas in something, likely epoxy.

    Here are 2 pics showing the finished results, note that the lower rail has a really poorly drilled hole in it...

    bottom rail, this faces down when installed.


    Top rail, looks great to me!
     
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