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Here is the exploded view of the rifle.
All of this can be done in the field within minutes:
http://www.robarm.com/XCR_Fieldstripped.gif

Here are some video links:
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The M4's problem is not just hot gas, its "dirty carbon" gas. The 416 is a nice upper package, but why not just overhaul the entire kit.
I would like to see a mil trial of the american made XCR by...