On a level of seriousness....two guns would have made more sense. A 57 with a longer barrel would have actually been a good choice because San Fransisco PD actually issued model 58 .41 Magnums. One of my all time favorite guns I ever owned was a SFPD marked 58 carried both at San Fransisco and later by a DEA agent. Harry carrying a longer adjustable sighted version of the duty gun would have made an interesting sideline. Portraying Harry as more of a marksman.

A .45 based gun like a 25-2 or 5 to easier run blanks.

Going with the .44 was calculated and created a interesting legend. In a funny way, had Milius went .42 Mag, it may have made that a cartridge of our time.