Unless the characteristics of the 9mm are changed, I have questions.
1. 9mm tend to go thru targets creating collateral damage.
2. 9mm do not have the stopping power of a .45 cal etc.
Now if these 2 issues are fixed with this change, sounds good to me. However, I didn’t see stopping power and collateral damage as issues in the change.
More bullets.
I believe it was in 2015 that the FBI released an extensive multiyear study of handgun effectiveness. They concluded that the "stopping power" advantage of the .45 acp or 40 cal was a myth. Physicians could tell no difference between the wound channels of 9, 40 or 45. They determined that the biggest factor in winning a gunfight was the ability to fire quick, accurate follow up shots. The study determined that the 9 was better at this at all levels of shooting ability (ie. from their best to worst shooters.) Obviously this was due to the lower recoil of the 9. This is why the FBI went back to the 9 and why many police departments are too.
Overpenetration? Only with full metal case bullets. Modern hollow points all behave similarly in the standard self-defense calibres.
Stopping Power? All handguns suffer from similar problems. The stopping Power concept as described by Marshall and Sanow has been discarded. All handguns rounds are too slow to cause the same stop that is seen with rifle rounds.I
Handgun effectiveness is a complicated and multifactorial issue!
9mm hollow points go in and just mess up things. They don’t go through much of anything.
9mm FMJ will penetrate (go through), but there is lots of good 9mm defensive ammo now (JHP and other types) that will transfer just as much of the energy to the first thing it hits as a .45 will. The gun is the same but the ammo choices have gotten much better.