Cold Metal Jacket

You magically freeze your ammunition, making the firearm cold to the touch. The next time you make a ranged weapon attack within the spells duration, your weapons damage type is cold. On a hit, the target takes and extra 2d12 cold damage on top of the base damage of the weapon.

On a hit, the targeted creature must make a Constitution saving throw and on a failed save the creature partially freezes, reducing it's speed by 10ft.

Upon a hit, the weapon and ammunition return to normal. 

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the damage of the spell increases by 1d12, and the Speed reduction is increased by 5ft (to a max of 20ft) for each slot level above 2nd.