The .44 Remington Magnum, which actually has a .429" diameter, is a rimmed revolver round. Introduced in 1955 as a more powerful version of the .44 S&W Special, very much like the .357 mag which is a souped up .38 Special. (.38 Special is actually .357")
The .44 mag is perfect for shooting game animals up to full grown deer. It is also excellent in people who break and enter your home and threaten to hurt you or your loved ones. Yes I advocate the shooting of such people.
Its ability (or any other round for that matter) to do a one shot stop can not really be put into an accurate numerical coefficient as there are much too many variables to be taken into consideration.
Follow me to the chronograph if you please
We'll be using a .357 mag S&W revolver with a ten inch barrel and will be launching a 180 gr bullet loaded to maximum recommended pressures of ADI cannister grade smokeless powder.
reading: 1,308 fps
Now we'll fire a 265 gr .44 mag (also loaded to maximum recommended pressures) from a 14" barrel revolver.
reading: 1,183 fps
.357 mag == 235440 power factor
.44 mag == 390875 power factor
The reduced velocity of the .44 mag is more than made up by its added weight and hence momentum.
power factor == weight in gr * velocity in fps
NOTE: power factor is different from stopping power.
I would gladly answer any firearm related queries, please do not take video game weapon statistics as fact, yes that includes AD&D too.