I havenever heard of a .54 cal but no, a bullet that will not stay in place for the striking pin will not fire, DO NOT TRY IT, if by some off chance that the striking pin hits the firing cap then the...
9 millimeter is the caliber. IMPROVING ANSWER: A "9mm" bullet is actually .355 or .356 of an inch in diameter. So the caliber is about .36, but nobody calls it that because it would be confusing....