The term “final protective fire” means the highest priority is given to this request due to the danger of a position being overrun. For the guy in the trenches, that means firing as fast as possible to break up a determined assault — even if that uses up barrels and ammo fast. If the FPF fails, there won’t be a “later” for those troops.
How does this relate to civilian self-defense? Very directly: almost every defense against a foe with a contact weapon is an FPF event. Most short range shootings are the same. They are rapid affairs with very little care given to the aftermath — if you fail to stop a guy with a shank, there won’t be an “after” for you. The difference is that you seldom have another person covering you and have to rely on your own firepower to break the attack.
There’s another, far less common case where the same considerations come up — riots and civil disturbances. Unlike personal defense events where attackers are usually few and retreat is sometimes an option, a large-scale civil disturbance doesn’t leave many safe havens. Your home or place of business ends up being the safest location. Having non-combatant dependents with you — such as kids or infirm grandparents — limits your ability to maneuver, while the flimsy construction of most modern homes and offices makes them poor cover against incoming fire. One way to deal with threats in that environment is to outrange the attackers in both firepower and the ability to spare innocent people. Gangbangers going after a juicy target don’t care who they shoot — but you ought to care. It’s good to have the ability to take a precise 200 yard shot against a hostile shooter and still be agile enough to break a rush at 20 yards. As LA riots showed, Molotov cocktails are no joke in urban areas.
Suppressive fire does have a place in such situations: you don’t really care if you kill the foe as long as they are prevented from killing you. The lack of automatic capability isn’t too big of a problem, because it reduces the problems from the lack of interchangeable or watercooled barrels. Thirty rounds per minute is sustainable for a medium/heavy AR15. A hundred would not be for long, but it could come in handy in case of push coming to a shove. While you are unlikely to face a human wave attack, a stolen commercial truck used to crash your neighborhood watch barricade would take a lot of stopping when all you have is a rifle.
This rifle is not shown with a bipod because of its dual long/short range role. Sandbags or other improvised supports would keep the shooter less visible than a bipod, and the forend thermal wrap combined with a VFG would keep the support hand from burning. Smaller magazines would work fine, but there’s something comforting about 150 rounds on tap in a reliable drum.
The rifle, incidentally, isn’t fully mine. The upper was acquired by a friend, a veteran of the South African civil war as an addition to the shorter-range arms. He’s concerned that the US situation may call for such a tool in the near future.
The thermal wraps, by the way, work just as well for three-gun competitions or a long day at the range as they do for stopping hordes of zombies in the wire.
Most equipment would do if you can. That said, an effective range of a 30-30 with open sights is under a hundred yards, while a an AR10 with a variable scope might stretch out to 400 and still be as fast at room distance. While I like having good gear on hand, I think that a dry run through the neighborhood with SuperSoakers or nerf “guns” would do as much to improve the defense plan as a day at the range. Given the cost of ammunition right now, the tactical exercises may be worth doing in preference to more trigger time. Finding ways to join forces with neighbors would be a help as well, since a typical family with two adults cannot hold a fixed position against even a slightly competent assault for any length of time. 24 hour/360 degree watch would be too hard to effect. Exceptions to that would be locations where the approach can be properly channeled, but that’s not the case for most of us.