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I have a 20” Kreiger dcm profile installed in a bcm4 upper with a geissele rail. No problems so far. Negligible poi shift when on a bipod vs on the mag. I’d go for the tighter fit. That will help insure the bolt lugs having an even load in my opinion. Of course, my opinion is worth what you paid for it.
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I appreciate everyone's advice. I went with the Vltor MUR, and will see if it ends up shooting as well or better than the build using the BCM4 upper. It'll be a good month or so before I can really wring it out.