caliber:
1.
the diameter of something of circular section, esp. that of the inside of a tube: a pipe of three-inch caliber.
2.
Ordnance. the diameter of the bore of a gun taken as a unit of measurement.
cartridge:
2.
a case containing any explosive charge, as for blasting.
3.
any small container for powder, liquid, or gas, made for ready insertion into some device or mechanism:
an ink cartridge for a pen.
They are NOT the same thing!

[&o]