Quoted:
I would disagree with most that rounds like the 300 BLK are not for long range. They may not be IDEAL for long range in a typical application, but if you know your drop and understand the limitations, it can VERY effectively be used at that distance - in the proper application.
Think of it this way:
What is the drop of a .338 Lapua Magnum at 1000 yards? The factory load has dropped 137" at that distance yet nobody will argue that it is perfectly OK to shoot this cartridge at those distances.
The 300 BLK at 250 yards, using the 240 SMK at 980 fps will have dropped 119" (less than the Lapua, I know, but it is close enough for our discussion), so arguably it should be perfectly OK to shoot at those distances
At longer distances, you may not be able to strike a moving man-size target (or a deer) but you might still find use in other roles - vehicles can be disabled, a parked car (hood) is a very manageable target at 500 yards... it just depends on your application.
If you wanted to dissuade a group of unwelcome visitors from proceeding further, it would be feasible to fire a burst of suppressed 240 SMK SS loads, which would land in a nice spread, while the shooters location will be difficult to discern. Hogs seem to be rather displeased when you do this.... other "critters" might be similarly discouraged...
Just have to understand how to use it and then make the most of it...
Its not about inches of drop, its about angular drop.
137" @1000yd is about 13 MOA. 119" @250 is around 45.5 MOA. Literally over 3x as much elevation correction as far as scope adjustments go.
Subsonics are hell on drop beyond 150yd, regardless of what caliber. The only subsonics that I would use to kill something past 200 with would be .50 750gr amaxs. Or 750-800gr solids in downloaded 50bmg or 50 thumper/ 510 whisper and the like. Drop is still shitty, but at least the bullet is big enough and aerodynamic enough to have substantial energy, even out as far as 400-500yd.
A subsonic 30 cal that has traveled over 300yd isn't going to do much to a vehicle. It will cause damage but not much.
If you want long range AND the ar15, 6.5 grendel is the ticket.
Eta: suppressed subsonics do very little in the way of scaring or suppressing people. I remember 1 account of a sniper in vietnam using a silenced smg in a firefight. Another person with him would fire bursts of unsuppressed rifle fire and the enemy would dive for cover. The sniper would shoot suppressed smg bursts and the nva often didn't respond at all, like they didn't know they were being shot at.
Suppressed supersonic rounds are another story. You still get the crack overhead, without them being able to hear too precisely where it came from.