I have two 9mm carbines. One is the Beretta Storm carbine and the other is an MP5. Both with rifle length barrels.
The Beretta is by far the most accurate and other than Remington Green box the only thing I shoot is hand loaded Lead. Under 6 inch groups are easy at 100 yards. The bullets I use Penn bullets 120 GR Truncated Cone. I use his premium grade which in 44 magnums I have pushed up to 1900 in a rifle. The most accurate is with a 231 load and has been croned at 1300.
I have tried 147 Gr from the same manufacture which worked well in a handgun but accuracy suffered in the carbine.
Why are you shooting 9mm in a carbine?
Because they are cheep to shoot (9mm reloads are under 3 cents per). Good practice rounds since you can shoot them all day because they are cheep. But the number one reason is that they are fun.
"The difference between stupidity and genius is that genius has its limits" Albert Einstine