I just passed firearms qualification with 3 calibers, back-to-back-to-back, all on the first go.
1. 40 S&W with my stock G23
2. 9mm with my G26 fitted with a G19 barrel and magazine plus grip extender
3. 45 ACP with a G30 range gun
I was going to use a range gun for 9mm because I haven't been shooting the G26 well. But, I did so well with the G23 that I went ahead with the G26.
This was easy to do, due to the common operation of all Glocks. I also believe that Glocks, right out of the box, are a known constant. Therefore, I believe I could qualify with ANY caliber Glock with no preparation.
I gotta get me a G30. 10 rounds of 45 ACP in the same package size as a G23.