Glock 20s are 10MM...sort of an auto 41 Special...Sometimes called a Block 20, it does hold a bunch of ammo. May may not be a good fit with average size hands. Borrow or buy a used Glock 9MM, then use that skillset when you upgrade to the Glock 20.
The advantage of revolvers is they can shoot low powered ammo for skill building working up to full power ammo for serious matters.
Auto pistols need full power ammo to function.
