It fires 5.7x28mm.
Depending on what it is chamberd for, yes.
No. A smaller caliber will either not fire at all, or will split the cartridge casing if it does fire.
.45 ACP
Winchester Center Fire.
The Fabrique Nationale P90 personal defense weapon is chambered for the 5.7x28mm bottlenecked cartridge.
In most circumstances, no. The bullet is too large to chamber in the handgun.
It fires a 7.62x51mm NATO bullet, which is similar to a .308 Winchester.
If you fire a .45 caliber bullet at a paper target, it will leave a .45 inch hole.
Any that have the appropriate sized barrel
Generally speaking, no. You can only fire the caliber for which the gun is chambered. There are some exceptions, but not many.
That depends on the caliber of the round of ammunition.
It's a .30 caliber bullet.