Are you talking about something like the Aguila "Super Sniper Subsonic?" That bullet is 60 grains, and is designed for a different twist rate (1:9) than the normal 40-grain .22LR load. Here's an example of a rifle barrel designed for the Aguila SSS:
http://www.gmriflebarrel.com/productdetail.aspx?id=901603If folks aren't having much luck with the SSS out of a handgun, I'd suggest it might have to do with the rate of twist. If one is looking to the larger bullet for a bit more "oomph," maybe something in .22WMR might fit the bill?
The "normal" subsonics, with 40-grain bullets, are popular at my club for club-level competitive target shooting. They will often offer better accuracy than the bulk pack ammo, at a price lower than true "target" ammo. The theory is that when the bullet in a "normal" load goes supersonic, there is some disturbance to its flight. With ammo that never passes the speed of sound, you supposedly eliminate this variable.
Don't shoot me, I'm just the messenger. I shoot mostly bulk pack...