AirPower,
I am not a fan of the .40 S&W, preferring the .45 ACP in autoloaders and the .357 magnum, .45 Colt, and the 10mm in revolvers. However, I must disagree with your statement “So what good is the .40S&W, if it's just another caliber to go the way of the 10mm and 41mag?â€.
First, neither the 10mm nor the .41 magnum are dead, and both have strong advocates – for VERY good reasons, if you analyze these rounds’ quantitative attributes. Significantly, last year Glock sold more 10mm semiautomatics than ever before (according to a thread on TFL).
Second, “compromise†is frequently a VERY good thing, since it is the ideal methodology to ensure quantitatively balanced and optimized results. This is especially true when valid analyses suggest that a combination of attributes (such as magazine capacity, diameter/cross-sectional density, mass, and velocity) provides the most advantageous solution for selected applications (such as law enforcement).
To illustrate, using the .40 S&W in "field" law enforcement functions:
> Magazine Capacity is better than the .45 ACP, the same as the .357 Sig, and slightly lower than the 9x19
> However, mass and diameter are better than both the 9x19 and the .357 Sig, although worse than the .45 ACP
> And velocity is much better than the .45 ACP, about equal to the 9x19, and marginally worse than the .357 Sig
For ease and simplicity, I have weighed these four attributes equally (I am NOT suggesting that is the appropriate way to evaluate this question, but it is fast). This yields (lower score is better):
> .45 ACP – 8 Points
> .40 S&W – 8 Points
> 9x19 – 9 Points
> .357 Sig – 9 Points
To summarize, I am not a .40 S&W advocate. However, in a multi-variable analysis (for law enforcement applications that demand capacity, mass, velocity and cross-section) the “short and weak†is probably a fine compromise. Personally, I much prefer the 10mm – which employs the same bullets in its lower-mass applications – but the FBI’s migration to the .40 S&W probably forever eliminated the 10mm from wide LEO use.