That was the explanation in the novels and movies. The true reason was that Ian Flemming was told that the Beretta 418 was more of a purse gun for women. They quickly changed his gun for a Wather PPK, but in actual fact James Bond in the movies carried a Walther PP ( it is a bigger version of the PPK )
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With all due respect CC, if that was the answer you were looking for, then I think the wording of your question was ambiguous. I suppose there's no simple way of asking the question without hinting at the answer, but I think most would agree that my answer would still be considered correct, given the way the question was posed.
Insofar as the movies CC, Bond had carried the Walther PP only once, in
Dr. No, and in the subsequent films carried the PPK (either chambered for .32ACP or .380ACP), along with the P99 & PPK/S (which was actually a regular PPK dressed up with the micro-dermal sensor grip) as his standard issue sidearm. Although the overall shape of the pistols are similar, the PPK has a shorter barrel, slide, and grip, and is more suited for concealed carry under Bond's suits or signature tuxedo.
http://www.imfdb.org/wiki/Walther_PP_Pistol_Series
And if you look at the following stills from the films, you can see the difference between the extended slide of the PP versus the compact slide and barrel profile of the PPK.
Promo still from
Dr. No with Sean Connery and the Walther PP
Connery's PPK
Lazenby
Moore
Dalton
Brosnan
Craig