9mm effects

Is it possible to have a .22 pistol with a 9mm barrel?
and if it is what effects will this have on the gun?…will it significantly improve the gun or not really?
No.
A gun needs to have a chamber and a barrel that fit the bullet size, caliber, precisely in order for the bullet to be forcefully pushed through the barrel with just the correct amount of resistance to create a seal yet still move forward and out of the barrel.
Were you able to fire a .22 rimfire cartridge into a 9mm barrel, the gasses would escape and probably not push the bullet out. This is simplified…..it will not work for a whole lot more reasons as well.
After Effects Gun Shot Effect 9mm with lighting fz18