There are other problems that come up from that anyway.
First, bearing are, majorily, round. In order to load a bullet into a metallic cartridge, you need it to fit snuggly within the casing, which is not all that possible with a sphere.
Second, you’d have searling problems. Modern bullets have good sealing because of their shape which gives them a lot of surface pressed against the inside of the barrel and rifling.
Third, you would fuck up your rifling insanely hard. Ball bearings are insanely hardened whereas bullets are made or have soft metal jackets that let the rifling dig in. With bearings, your rifling would be pushed by the hardened projectile, especially since it applies on a very small surface, unlike with a proper bullet.
Fourth, it would have absolute shit ballistics. Bullets are made a certain way that makes them aerodynamic and that also makes them have good effects one they pen something (hence why they’re usually made out of soft metal, again).
Plus, 9mm balls mean you have huge fucking huge goddamn bearings that you’d find nowhere but in very heavy applications.