When it comes to dealing with Congress, it's often necessary to re-state the obvious. Sister Mary Ann Walsh, spokeswoman for the U.S. Conference of Catholic Bishops, does that well in this Washington Post piece explaining why it's pro-life to ban assault weapons:

The churchs pro-life stand against abortion is undisputed. So is its pro-life stand in opposition to the death penalty. It can only be justified if there is no other way to keep a deadly criminal from hurting more people. And in the most recent and all too common threat to human life, the church opposes the growing preponderance of lethal weapons on the streets. It stands as another important pro-life position.