9mm has more stopping power than .38... You will be fine with 9mm...
"The 9mm Luger meets these requirements with quality ammunition just as good as the .40 S&W and 45 ACP. The FBI 9mm test don't lie! Any brand of premium 9mm 124gr or 147gr JHP has the stopping power do the job!
My favorite is the 124gr hollowpoint ammo for defense. I use any brand I can get a good deal on. The reason for the 124gr choice is; I can practice with the low price 115gr FMJ made by Remington UMC and Winchester white box. The 124gr point of impact out to 15 yards is almost identical to the 115gr FMJ.
Your Captain, Chief, or sheriff may be old school and remember some of the 9mm pistols from 25 years ago that were cheap made or very heavy. He may also remember the crappy 9mm ammo from 25 years ago too. This is why so many officers are required to carry lower capacity 40 S&W or 45 ACP pistols, even though you may run out of ammo in a gunfight. The FBI has tested todays 9mm ammo and it has proven to be just as terminal as 40 S&W or 45 ACP. Cops carry 9mm pistols In Europe, Russia, Japan, China, Korea, India, and the middle east. Over 90% of the world's police use 9mm!
Premium 9mm ammunition cost as much as 45% less, thus giving police officers more range time without breaking the budget."
CCI Speer Ammo (Gov. Test) Bare Gelatin Expansion
9mm Gold Dot JHP 115gr 12.8" 0.67"
9mm Gold Dot JHP 124gr +P 13.40" 0.68"
9mm Gold Dot JHP 147gr 14.80" 0.57"
40 S&W Gold Dot JHP 165gr 13.05" 0.65"
45 ACP Gold Dot JHP 185gr 11.95" 0.68"
http://www.best9mm.com/9mmballistics.html