IMHO, after building an AR I kind of came to the conclusion that, prior to me building another, I needed to decide whether I favor defense or distance. I went this route because I think an AR dedicated to defense and an AR dedicated to longer distances at a range allows each to really excel in their specific purpose.
I think this is one of the biggest reasons many AR owners purchase or build multiple ARs given the versatility of the platform. My first AR build was initially intentioned to do defense and distance, but during that process I shifted to strongly favoring home defense. I'm gearing up to build another AR for the purpose of pushing 5.56 upwards of its limits to use at a 600 yard range I shoot at. For what it's worth, the following is my personal opinion.
DEFENSE - Design factors I quickly started favoring after initially starting the build as a multi-purpose AR...
Form factor vs. bullet velocity - A compact form factor makes moving about in smaller spaces easier to do, and the velocity sacrifice of a shorter barrel is not a big issue given it would be used at closer ranges.
Optics - Many of the simplistic and inexpensive sight options are incredibly well suited to defense, and durability takes preference over features or distance. Iron sights are durable, cheap, and work great. Certainly, the close range illuminated offerings from companies like Trijicon, Aimpoint, etc. are nice, but I think an AR used for defense should always have iron sights, even if only for use as a secondary backup. Any sighting system I use on a defensive AR needs to be very robust should the firearm be dropped.
Triggers - The trigger weight for defensive shooters are often intentionally heavier, and it doesn't make a big difference whether you are using a factory single stage trigger or a high-end single or two-stage target trigger. Given high-end triggers can cost hundreds of dollars, this is where money can be saved
Mags - Magazine wise, I favor mags constructed from steel with an impeccable reliability record (i.e., a brand/model known for avoiding feeding issues.) If the mag cannot survive being dropped on hard ground when loaded, I don't use that mag for defense and instead use it at the range only
Accessories & Rails - There are a lot of defensive accessories that can be very useful for home defense (for example, a high-output flashlight that has a button connected to an added secondary pistol grip.) In order to mount these accessories, a flexible rail that uses a standardized size is necessary.
Suppressors - ARs are loud as crap. Fired inside without hearing protection, ears can be damaged big time. While AR cans do not come close to eliminating all sound, even with supersonic ammo it is still a considerable sound decrease. The reduced sound and flash may also lower the chance that an assailant is able to use sound/sight to rapidly find you after you squeeze off the first round.
TARGET - having had the chance to see what design styles I favor for home defense, it is helping me determine what I want my next build to be like...
Form factor vs. bullet velocity - A longer barrel isn't a big deal and can increase bullet velocity. The excessive weight of a heavier barrel isn't a concern, even if a very heavy bull barrel is used.
Optics - Shooting past a certain distance creates the need for magnified optics (there's no consensus on exactly what this exact distance is, but if I am shooting much past 25 yards I am using magnified optics). The scopes I use on most of my rifles are not designed as tactical scopes, and if dropped they may break.
Triggers - The AR I am building is getting a Geissele trigger, which is a 2-stage trigger and adjustable. Stupid expensive, I can only bring myself to shell out that much cash for a range queen
Mags - I use a lot of cheap plastic mags given a feeding issue isn't a big deal. These mags are prone to breaking if dropped on hard ground when loaded. I also have one of the ridiculously large mags that I also only use for the range.
Accessories & Rails - The rail going on my current build is designed only to mount a single scope, and perhaps a bipod, although I prefer to shoot from a Caldwell bench
Suppressors - When I go to a range, I know when I am going to start shooting, giving me time to put ear plugs in prior to doing so. In a defensive situation, I wont have that luxury.
