There are so many damn guns, you know? (Acutally Blaft has put a lot of guns on the covers of our own books too, and sometimes I feel guilty about it. Dear customers: Promise you're not going to get all inspired to start stockpiling firearms and become all trigger-happy like a bunch of psycho American National Rifle Association members. OK? Please?)
This guy's blog has some nice examples of older covers, including some that appear to be Shelle's work. And there are a bunch more in the nice online collection here.