How to make explosions deal more damage? And how to improve sniper rifle?

Im making this bazooka, when the projectile hits entity/block it makes an explosion, but the explosion deals only like half a heart damage. Is there any way to make it higher? Like some sort of block "deal damage xx to entites in perimeter xx blocks" 

Im also making sniper rifle, everything is just fine, but i thought there could be some sort of zoom (i doubt that is possible without coding) or at least some overlay, like the black screen with circle in the middle. Can I do that?

thanks