Flaming in 3..2..1...not; I asked the same questions myself. I purchased the DD Lower from Grant to go with the BCM 16" light weight middy upper you are talking about.
DD Lower is more of a flat black and the BCM upper is rather shiny. The difference is not very noticable once you lube / clean the rifle after a trip to the range. I'm pretty stupid about these types of things and what little difference there is does not bother me in the slightest.
Fitup between the two is good not great? (don't know as this is my first rifle) Hold the rifle up to a light and you can see a gap betwen the upper and lower. About two pieces of paper thick. The gap did not seem to bother the rifle when I put 350 rounds down range last Saturday

. I'd think a little gap is ok and will keep the upper and lower from wearing where they meet?
I ordered the DD from Grant (after much anguish

) and do not regret doing it. The fact that Grant can build it out for you to your specs is what sold me! (flared magwell did not hurt either).
I'm very happy with the combination; and I would recommend it. Accurate, a dream to shoot, and one slick looking weapon. I'll try to get some pictures posted in the next day or two.
Grant, if you read this thanks!
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