Here's a primer. More can be found with a search I'm sure. http://www.defensivecarry.com/vbulle...host+connector
I don't know about swapping the G21 for the G30 trigger. I do know I've put the G17 smooth trigger in my G27 though. And in the baby 40 cal Glock, and a range practice of a mere 100 rounds makes a lot of difference with the smooth trigger compared to the serrated for sure. I'm not torturing my trigger finger any more! We'll have to do some research on the 45 auto Glock trigger swaps. I've never heard of it yet.