I've been wondering if anyone besides myself keeps shot count books but have put off asking until I saw it mentioned in another thread yesterday. I used to keep small notebooks in my range bag but I don't actually keep books anymore, now I keep the information on my computer. I track the number of rounds fired, the brand and type ammo and magazines I used. I've got 13 mags and they're all marked so I can tell them apart. If I have a hiccup like a FTE or any other problem I make a note of it so I can see if a problem is developing. This makes knowing when preventive maintenance is due, like spring replacement before I start having problems. How many rounds do you have left on your recoil spring or firing pin and mainspring, I know exactly where I'm at on each of my guns.