First off, thank you for taking the time to answer my questions! I live in an urban environment (near Portland, OR), so I'm thinking that an SBR 5.56 might be a smarter way to go for me in a defensive rifle than, say, a FAL, but I just don't know that much about long guns. I'm looking into ARs and other defensive rifles(I'm a total newb to them) for defense, just plain old fun, and SHTF, in that order, and I'm having a hard time getting a straight answer or three on the following: When you drop barrel length below 16", how much effective range do you lose at what rate with a 5.56mm? How does changing to 6.8SPC or 6.5 Grendel change this? In effect, is 6.8 the way to go below 16", and why? Does 6.5 out of an SBR even make since, or is it just a long range round that should be left to DMRs? What about 7.62? Does it also lose a ton of range/power out of a shorter barrel? Would going to something like a D S Arms SBR be the way to go or a waste of a good cartridge? While you're here, answering a ton of questions for me out of the kindness of your heart, what do you think of the Robarms XCR? They look cool to me, but it's totally possible that I'm just dazzled by the shiny. A pro's advice would be very appreciated!