The Sky Gun

You summon a portal in the sky and a hand that's holding a gun come out. The hand will shot the target of your choosing with a really high precision. The target must do a saving d20 dexterity saving throw.
If the target roll 5 or under, The target will receive a headshot or the target weakest spot and 2d20 + 5 piercing damage.
If the target roll 10 or over, The target will receive a shot to the chest and 1d20 + 5 piecing damage.
If the target roll 15 or over, The target will receive a shot to the shoulder and 1d10 + 5 piecing damage.
If the target roll 16 or over, The target will receive a shot to the leg and 1d4 + 5 piecing damage.
If the target roll a 20, The hand in the portal on the sky will surprisingly missed the target even though the legend say its never missed its target.

If the caster level 15 the hand will do a "Double Taps" and shot twice instead of one.
If the caster level 17 the hand will do a "Trippel Taps" and shot thrice (Other word for three time) instead of twice.
If the caster level 20 the hand will be get "Super Precision" shot will always shot the target in the head or at the target weakest spot.