The KAC 2 Stage trigger literally can be "tuned." And I'm probably not using the correct phrase to describe what was happening. I pulled the trigger once and two rounds came out...after two or three times of this occurring I swapped lowers to one with a CMMG LPK and the problem did not reappear. The two lowers had the same brand buffer, tube, and spring. Only difference was the trigger.
I am going with Leupold because it's the "correct" optic for a Mk12. Basically I am building a Mk12 Mod0 clone, so trying to keep the parts as correct as I can.
Personal preference, but my SHTF gun would be a close/medium range weapon (ie: AR-15). I have a tricked out M1A for distance (not a bolt gun but it's still sub MOA), the soon to be completed Mk12 for an SPR, and an M-16A4 clone for shits and giggles.
I haven't heard of anyone having reliability issues with lightened BCGs. In fact, the competition (3-gun) competitions are full of them and reliability is just as important to them as to anyone else. Really, I don't think light weight AR's sacrifice any reliability compared to a full weight. Sure, if you ran over a polymer lower with a tank I am sure it would crack...but baring that unlikely scenario... What part has you worried?
(And the barrel for my lightweight is a 14.5 that will have the FSC 556 pinned to bring me over 16" so it's not an SBR...damn you Illinois!)