It is now generally accepted that you have to dry-fire or have lots of ammo to get good.
Steve Anderson is credited with the first book on dry-fire.
It is not just a book but a log of your progress.
I must admit I didn’t write down my part times in the beginning. I tried the drills without a timer and thought, “Okay, these drills could improve my shooting” but I didn’t think much of the book. It wasn’t until I started doing the drills with a timer and writing par times in the book that I got better. You see, when you go through the drills you decrease the time by just a little every time. Doing the drills without trying to make a par time does not help you get faster or more importantly more consistent.