No. Most powerful handgun can be a bit ambiguous, considering that many short barreled rifles are sold in the US as handguns, minus the buttstock.
As for purpose made and designed pistols, in the traditional sense, firing a dedicated handgun cartridge, the answer still is no. The most powerful production pistol in the world which fires a dedicated pistol cartridge is the Pfeifer Zeliska revolver. It fires a .600 Nitro cartridge. There are several other dedicated pistol cartridges which eclipse the .44 Magnum in terms of power - .454 Casull, .50 Action Express, and .500 Smith & Wesson Magnum are some of the better known ones.
Even when Clint Eastwood claimed in the movie 'Dirty Harry' that the .44 was the most powerful handgun cartridge in the world (the movie was released in 1971), he was already outdated - the .454 Casull had already been introduced in 1959.
The .500 S&W magnum is the most powerful handgun round commercially available.
Dirty Harry used a 44 Magnum in his words "The most powerful handgun in the world." Specifically, it was a Smith and Wesson Model 29 in a .44 magnum. In addition, it is not the most powerful handgun in the world (not even at the time of filming.)
It was a Smith and Wesson 44 Magnum "The most powerful handgun in the world" according to Harry.
A VERY good handgun- for most puposes. Durable, reliable, accurate, and powerful.
.357 magnum Actually, a more correct answer is, MOST 357 is more powerful and MOST 45, but there are a couple of exceptions, if you are talking about muzzle energy.
No
Unknown
Probably, almost certainly, the .600 Nitro Express is the overall most power handgun bullet. Let me alter this answer by saying the .600 Nitro Express is a rifle round that one company made a pistol for. The most powerful handgun cartridge is the 500 S&W Magnum.
Six
Factory, I'd probably say the 500 Magnum
The .500 S&W Magnum is the most powerful handgun cartridge in production. Smith & Wesson Model 500, most powerful revolver. There are other handguns that are larger but are not in production. One off customs etc.
Not even close. There are several more powerful handgun cartridges, not counting the single shot pistols that use rifle cartridges. While Dirty Harry may have proclaimed it to be "The most powerful handgun in the world"- it is not.