Bombs and Sniper Camera

I got 2 questions:

1: I made a bomb and when I throw it it should kill all the enemys in range of 50 meter fron the bomb. Can someone explane how to do that because I don't know how? (The bomb needs to have a collision with everything).

2: I want to create a simple sniper. to use the weapon I need to activate the camera on it for aiming with keys because it a third person game and I don't use the mouse. How I press a key, activate the camera on the gun, when the camera works see the sight GUI, rotate the camera with the keybourd keys and able to walk while it works (to go back to the main camera I can do by myself after I will know how to do what I asked)? I don't know how to do it... the sniper don't needs to have a zoom.

Sorry for poor english (as allways..).

if (Input.GetKey ("P"))
{
    GameObject.Find("Camera").GetComponent("Camera").active = false;
    GameObject.Find("Sight").GetComponent("Sight").active = true;
    //Change camera to the sight when you press P
}

Attach the "Sight" camera to the sniper, then simply have a GUI skin attach to the "Sight" camera.