Can you shoot a 40 caliber bullet from a 45 caliber gun?
The short answer is no. The longer answer is, you might be able
to get a .40 caliber cartridge to fire from a .45 caliber gun, but
it may damage the gun, and even if it doesn't damage the gun, it
will cause other problems. In general (with only a few exceptions)
you should never try to fire any cartridge in any gun other than a
gun designed for that caliber.