Is 300 Blackout worth it over 5.56?

300 Blackout earns its keep in one role: short, suppressed, close-range guns running heavy subsonics, where a short 5.56 struggles. It uses standard AR mags and bolts (just swap the barrel). For everything else, 5.56 is cheaper, flatter, and longer-ranged. Build 300 BLK for a quiet SBR/pistol; otherwise stick with 5.56. And never mix the two in the same mags — a 300 round in a 5.56 barrel can blow up the gun.