Btw OP, the mag looks sweet.
I was unaware that it is now illegal to install a non hbar upper on a lower legally purchased before October 1. I would very much like clarification on this because it is the lower and the lower only that is registered it is the same as buying the complete rifle were as uppers are just a part like any other. I'm not saying this is incorrect just that I was unaware. It seems to me putting a a non hbar upper on a lower would be legally no different then replacing a trigger guard on a complete rifle or even switching uppers on a complete rifle already owned before October 1 because you are not legally constructing a firearm it already is at the point you bought it. That's kinda like saying since you can no longer buy magazines over a 10 round capacity you can't put a 20 round mag in your lower now
Nor can you put a non-HBAR upper on any md legal gun purchased post 1 october 2013.