Kinetic Bowstring
This magic bowstring can be used to string a nonmagical bow or crossbow, turning any attack made with it into a magical one. A kinetic bowstring magically amplifies some of the stored kinetic force that it releases when it fires an arrow or bolt. The first ranged attack you make on each of your turns using a weapon strung with this item has twice its normal range, and on a hit, the attack deals one extra die of its damage.
"Wait. You're telling me this releases more energy than I put in?" "That's correct, sir." "But how? Like, from a physics perspective. If I pull it back so far, it can only release an equal amount of potential energy to loose the arrow." "As I've said before, sir, I just work here. You'll have to take it up with the master enchanter."