Ammo shortage, I could understand.
The new, modern bullets used in 9 mm are also used in 40 S&W.
A bigger, heavier, bullet at faster velocities like the 155 gr & 165 gr bullets are going to out perform any 9mm +P or +P+ anyday .
Those +P+ rounds really chew up your gun too if used too much. I don't know why more depts. don't use the hi-cap 45's that are out.
With the 200 or 185 gr +P loads they are super deadly. Hitting with 479 to 535 ft-lbs of energy, they could take down a 350 lb man with one shot !
Even with the +P loads, in 45 they are reletively low pressure compared to 9mm +P, +P+, and 40 S&W. Most 40's however are built to withstand the hi pressure.
In Phila, PA cops have the option to carry 9mm, 40 or 45. I know three officers who switched to 45 acp. and they say it's the best thing the dept has done in years.