It might be the vastly improved trigger feel and grip, and I know it is hard to fathom, but I think it is eaiser to shoot rapid than the 9mm. It would be interesting to shoot a 9mm with the new grip and trigger however.
I just got back form the range with my M&P CORE 9mm, and it is shooting about 8" low at 7-25 yds. I was shooting 115 grain ammo, and I could possibly try 147 grain and see how it shoots, but my other 9mm's like the 115 grain, and with 4k rounds on hand I would kind of like to shoot the 115...
I am the owner of a Shield 9mm and a Shield .45 which I just shot today. I shot 50 rounds of Remington 230 grain H.P. through it and all I can say is this thing is a *****cat. The trigger is vastly improved and the new grips flat work. I shoot it he best of my 3 single stacks. Rapid double taps...
The report I saw said bigger is better, but the new FBI report states that with the much improved bullets and powders the9mm is more effictive than a .40. A fmj 9mm will make a small wound channel that seals up, which is most likely what the ER docs are seeing.