Mas, I currently own a Kel-Tec PF-9 as my only self defense handgun. I had a Glock 36 that was too tempermental for me to rely on for a self defense situation. I shot the M&P 40 today for the first time and absolutely loved it. From 7 yards to 25 yards all 50 rounds were in the 8 ring on a B-27 target. I am having a hard time deciding between the Full Size M&P and the compact as well as 9mm vs .40. The caliber decision is based soley on price of ammo. I want to be able to shoot as much as I can to become as proficient as I can. The 9mm would allow more shooting for due to being $19.97 for 100 rounds vs $27.97 for 100 rounds of .40. As far as the full size vs compact, I want to be able to carry the gun comfortably, but also want the gun to be comfortable enough to shoot 200 rounds through at one time. My PF-9 is not fun at all to shoot due to the light weight. I'm sorry for all the rambling but I was wondering what your opinion is on my situation. Full size vs compact, and 9mm vs .40.