I actually just received to Armalite lpk's in the mail for two ar15 builds going on. In my personal experience they have the best springs and some parts are a bit stouter than on some other kit I've seen. More specific to you, buy the Amalite lpk, with their NM match trigger, minus the trigger, or/and grip if you have one you prefer,or order an ALG defense trigger to go in there. Here is a link through the Battle Arms web site…. hint hint for my preference on safeties!… but they are made in the same place as geisselle triggers in a facility they started for his wife. Geisselle quality, low price! I will be buying one for my wifes ar15 build, yes I have shot one, and while they aren't quite the same, they are far better than any other aftermarket entry trigger I have used. You may have to call Armalite to find out about your lower, but I don't think the Pmag lowers are out there yet aside from complete lowers, and my advice is save the lpk for your mk12 as back up parts! http://shop.battlearmsdevelopment.com/main.sc