One side of me would say that anything that is marked commercially with a number of "45" or smaller would be acceptable in court without much argument (like a 44 magnum).
The part of me that thinks like a lawyer (sad) says that if the bullet diameter is larger than ".45" like a 454 Casull or 460, it would be risky because the prosecutor would ask the expert witness "Is a 454 Casull larger than a .45?" They would likely answer "yes" And then the prosecutoer would say "so, Mr. Cornelius, you were using a prohibited caliber when shot the defendant?"
I'd think that in cross examination a prima facie based question would shoot that down. After all... if your shooting went south with a 45 ACP and the recovered unfired bullets that were surrendered for evidence miked out the .451... you could blow that apart easily. YOUR expert witness can produce reams of factory manuals, descriptions, gun articles etc that prove a ."45" is indeed a "45".
I'd be pretty confident that any lawyer could knock the wind out of any bullet diameter argument and win the point on the concept that "calibers are what they are- based on face value of what's marked on the gun or standard descriptions of the firearm>
Seeing that the 480, 454 C, 460 SW will all fire 45 Colt (and it's common knowlege) I could see that .454 is bigger argument going south pretty quickly too.
Unless you get a Obama-fan as your Judge LOL