I like the pragmatic way The Dalai Lama deals with life. He's an absolutely peaceful guy, yet without the absolute pacifism of some moral-posturing fanatics. Call it contingent pacifism.
This is what I take away from what I've seen of his advice to his followers, as it may pertain to defensive gun use:
One should never initiate violence, that much is clear. But it is also clear that one should protect himself or others when attacked unjustly, even if the only way of doing so is to use defensive violence. The person who uses defensive violence must bear the consequences of his actions, such as the risk of taking on karmic soul-debt, but nevertheless must act if he judges that the risks are worth facing to prevent a greater evil.
So then, violence is something The Lama can understand even as he disapproves. I am completely down with that.