[Travis McGee]

I fail to see the utility of converting to a submachine gun caliber. Modern body armor laughs at handgun ammunition anyway, you really need an assault rifle or battle rifle to penetrate that stuff.

Not to mention the drastic dropoff in effective range.

[Lurker]

I fail to see the utility of converting to a submachine gun caliber

The only reason I could see is if you wanted to use a supressor. If one wished to fire subsonic 9MM or .45 ACP rounds I suppose it might make some sense.

One of the private ranges I do 3 gun shoots at won't allow the use of 5.56 ammo, so quite often we use an AR with a 9MM upper for that event.

Those are about the only reasons I can think of.

L