It's interesting (to me) that the 9mm LCR is the heaviest one they make at 17.2 ounces (beats the .357 by one-tenth of an ounce, but still...) I wonder if that's due to the higher expected recoil.
http://ruger.com/products/lcr/models.html
edited to add: I see the 9mm and .357 are steel, rather than aluminum in the body part of the gun.