Sholling is absolutely right about the plastic Kahr .40's being brutal on your hand. I had a Kahr P40 for awhile, but could not handle the whiplash effect of the recoil on my hand. I sold it after just a few months. All Plastic Kahr pistols are extremely top heavy.
I have since purchased a Kahr PM9, and have no problem with handling its recoil. The .40 is an entirely higher level of discomfort in a Kahr.
I do own a couple of compact .40's, though. My Smith & Wesson M&P 40 compact is very comfortable to shoot. It is a rather fat gun, though, with a double colum 10 round magazine. So it is not as easily concealable.
My other small .40 is my newest gun, which just came out a few months ago: The Walther PPS in .40 S&W It is more to handle than my M&P compact, but not anything like what my .40 Kahr was like. So while it requires a good strong, firm grip, it is manageable to control, and does not cause the pain I felt with my Kahr P40
Here is a comparison photo showing the relative size of my Kahr PM9, with my Walther PPS .40 S&W:
You can see that the Walther is longer. Height wise, though, the guns are extremely close. And the Walther is actually slightly thinner than the Kahr.
Length-wise and Height-wise, my S&W M&P 40 compact is about identical to my Walther PPS .40 However, the M&P is a significantly wider gun, as you can see in this photo:
The wider grip, though, helps distribute the recoil more, making the S&W M&P more comfortable to shoot. But it certainly is a drawback when it comes to affecting concealability.
Budsgunshop.com has great prices on both the M&P 40 compact and also the Walther PPS .40
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