Fact one; your beloved Beretta 21 has less than 60 foot pounds of energy, even when loaded with stingers or minimags, and has less energy at the muzzle
than a 380 pocket pistol has at more than 300 yards.
Fact two; your 9x21 caliber is not only unavailable pretty much anywhere in North America, it’s less powerful
than a plain-jane, over-the-counter 9 mm plus P.
Fact three; with full power ammunition, in any barrel length, the 300 whisper/blackout is more powerful than your 223 SBR.
Fact four; with subsonic ammunition, in any barrel length, the 300 whisper/blackout is more powerful than the 22 rimfire conversion kit on your 223 SBR.
Fact five; it’s faster, simpler and easier to swap between subsonic and regular ammo with the 300 whisper/blackout then with your 223 SBR.
Can you argue against any
of those facts..?