While I understand taking most of Hollywood to task over hypocrisy (such as George Clooney flying from LA to DC by chartered jet to testify before Congress about excessive American fuel consumption), I feel compelled to point out that merely portraying violence does not automatically make an anti-gun actor a hypocrite.
As Roger Ebert would say, it is not what a movie is about, it is how the movie goes about being about it.
Take Lee Marvin for an example. Decorated Marine WWII vet, with injury to a sciatic nerve from a Japanese machine gun bullet ending his combat tour. Marvin did not like guns, and was vocal about it. Therefore, one of his criteria for accepting a part was that violence should always be depicted as ugly. Marvin's movies, even The Dirty Dozen, would have at least one scene that would make most viewers cringe (for instance, the stabbing of the woman by Telly Savalas, or the killing of the General staff's spouses by grenades and fire).
Gratuitous violence, such as portrayed by Stallone, is another matter.