I took some more pics because I have better lighting today. The camera can't really capture this, but I can look right down into my front pocket and see the butt plate of the CM9. But what the picture does illustrate is that the CM9 kind of holds the pocket open by about 3/4"
I don't think it is a huge deal, it could be covered easily by wearing a loose shirt untucked, but it isn't as concealable as the R9.
With the R9, the pocket material just sort of folds over the top of pistol:
What I am learning from this is
1) The stated dimensions and weights on the manufacturers website can be wrong, or don't take into account how the pistol will really be used. For Rohrbaugh, I think that 3.7" height measurement is for the gun empty, from the bottom of the magazine well to the top of the slide. When I measure with the magazine in, from the bottom of the magazine release to the top of the sights, I get 4.0" For Kahr, the actual OAL of the CM9 is 5.625” - significantly different from the published OA of 5.42" (when you're talking pocket pistols, a .20" difference is significant).
2) It is very difficult to make decisions just comparing specs. Here are the specs for the R9 and the CM9:
Rohrbaugh R9Caliber: 9mm
Barrel: 2.9 in
Length: 5.2 in
Height: 3.7 in
Slide Width: .82 in
Width at thickest part of pistol: .95 in
Weight: 13.5 oz, magazine 1.6 oz
Capacity: 6+1 Rounds
Kahr PM9 / CM9Caliber: 9mm
Barrel: 3.1 in
Length: 5.42 in
Height: 4.0 in
Slide Width: .90 in
Width at slide stop: 1.0 in
Weight: Pistol 14 oz, Magazine 1.9 oz
Capacity: 6+1
The specifications seem very close, you might think that .08" difference in slide width won't make a difference, or .22" difference in OAL doesn't make a difference. But it all adds up for an overall total effect. Part of why the CM9 holds my pocket open is because the pistol is closer to the top of the pocket, part of it is because it is a thicker pistol than the R9.