A P99 is a great .40S&W pistol, but it is a
superb 9mm pistol.
That said, the only real downside to a .40S&W P99 is that it can be snappy, but that's a subjective thing, of course. Both are excellent pistols.
Positives of the P99 are:
-
better trigger (make sure you get the AS version, and not the QA)
-
better ergonomics
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better fit & finish
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no need to pull trigger for takedown
-
double strike capability (for what it's worth)
-
no problems firing lead bullets (due to traditionally-rifled barrel)
-
better mag release design (cannot accidentally drop mag when holstered)
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more durable finish (Walther still uses Tenifer treatment with blackening, unlike Glock, who now uses a different nitriding process with an easily-worn matte finish)
-
better reliability (all generations of P99 are reliable, without the issues Glock has from generation to generation)
-
designed from the start to be a .40S&W pistol (never heard of a KB in a P99)
Positives for the Glock 23 are:
-
polygonal barrel easier to clean (though few pistol barrels are that hard to clean)
-
easier to find replacement parts
-
accessories can be found in any gun store (though P99 accessories are easily available online)
Mags for both are not difficult to find, though mags for the P99 (or identical ones with the Magnum-Research-branded baseplate) run about $5 or so more each:
http://www.midwayusa.com/product/28...e-fast-action-40-s-and-w-11-round-steel-black
.