Let me explain the "Chicago Reload" to you.
You shoot a gun until it's out of bullets, then you throw it on the ground and pull out another gun.
Repeat
There is no reloading in a Chicago Reload - the gun is discarded. You're only limited by the number of guns you have. I've heard of a heist participant using 12 guns. If those were something like a Glock 17 with the mag extension, that's 21 rounds each - for a total of 252 rounds.....no reloads.