just wondering, i own more rifles and handguns than i can count, been around guns all my life, shot competitively, but don't know dick about subcaliber ARs.
what do i need to make one from a standard lower?  can i geta complete upper with bolt and a mag block and i'm good to go, just slap it on to the lower and find some mags?
(BTW, i bet the +p+ speer gold dots i carry/shoot religiously out of my glocks would be AWESOME in a carbine!)

I think you mean "pistol caliber" rather than "subcaliber".

Subcaliber referes to a smaller than normal bullet in a particular firearm.

But anyhow in awnser to you question, yes all you need is a new upper with bolt and either a mag adapter or mags that are modified to work in an AR mag well.

Quoted: Subcaliber referes to a smaller than normal bullet in a particular firearm.

right, like a 9mm in a rifle designed for 5.56mm.
no flame intended, i may be wrong as well.

Don't us any ammo.

RangemasterD is referring to bore diameter, not muzzle energy...