I don't know how that works. My G20 loaded up with a full mag of 230gr Double Taps weights a lot more than my spray. I haven't weighed it so I don't know how much more, but it's not slightly less than half. Maybe unloaded...
As with anything in life, you have to practice. That goes whether you want to use a gun or spray.
It greatly behooves people to get an inert can of spray and practice pulling off the safety and shooting from the hand and from the hip. When we teach Hunter Education, we have kids practice the motion of pulling the safety off with empty inert cans before they get full ones to actually spray with. When you watch people try to spray, at the bear charging demos, most of the time, the bear is on them before they can get it sprayed because of that. They panic when they struggle to get the safety off and then the spray is way off the mark.
You should do the same with a gun. Go out in the woods and roll something down a hill to practice something moving fast towards you. Make it so a partner can pull a rope or something standing off to the side of you(if he physically releases it and rolls it towards you, you would be shooting towards him, so DON'T do that) and then practice drawing and firing your weapon.