9mm luger v/s 38 special

Question
why is the 9mm luger more powerful than a 38 special, when the cartrige of the 38 special is larger? Is the cartrige of the 38 special filled with more air or different gun powder?

Answer
The 9mm Luger is also called the 9mm Parabellum. It has a bullet diameter of 0.355" while the .38 Spl has a bullet diameter of 0.357".

The reason that the 9mm Parabellum is "more powerful" than the .38 Spl is due to the cartridge  specifications, not to the outside dimensions of the cartridge case. SAAMI specs the maximum pressure for the .38 Spl at 17,000 PSI, and for the 9mm Parabellum it is 38,500 PSI. That means that the case wall thickness, the case design, and the gun must all be designed to accept this pressure. The pressures are achieved with various types and amounts of powder. So, for a given type of powder, there will be less of it in a .38 Spl cartridge. If you were to put in too much powder, it would damage the gun and be dangerous to the shooter.

Hope this helps!

Dave