I am on the quest to purchase a new hand gun. I am torn between a few options. I like Glocks from shooting experience, and I am really into Sigs, however their feel sometimes gets to me due to their large handles. After talking to my brother who has a new G23 I was telling him How I want to purchase what I mentioned above, and was leaning towards the 23. However to make it more complicated I am torn btw a .40 or a 9mm. I already own a sigma in .40 and I like the large caliber. However with a 9mm I can hold a little extra in the Mag as well as I am able to better control my shots. He mentioned to me (which was the first time I had heard of it) that I can get say a Glock 23 and buy a simple 9mm barrel and a couple 9mm mags and thats all. While it makes sense I would imagine there being more to it than simply popping the slide off and a mag out, and thats it... Can anyone else explain this to me further... Thanks