I got a couple of stripped lowers coming, and one build is going to be an M4 kick around plinker toy, and I like lightweight. SBR is a bit of a pain in my county, but I'll do it eventually. I'm trying to decide between 2 options for uppers: 14.5" with pinned vortex or one of the slightly stretched GI style flash hiders. I would start with a carbine gas system and GI handguards, but someday I'd add the Knight's rails for doo dads or even just for looks. Question 1: How are the Knight's rails? Do they move a ton, or are they relatively solid? I know they're not free floated, but that's not a big deal for me on this rifle...the other build will be the match rifle. 16" with mid-length gas system. Probably just a GI look to start with. Without pinning anything, I can swap stuff a lot easier. Question 2: Anybody have a good idea of the difference in weight between the 16" and 14.5" upper in a standard GI configuration (F-marked FSB, round handguards, standard profile barrels)? Thanks! -J.