Stormsnap is a Patreon Item and a high level bow that gains ranged strength and ranged attack bonus depending on the magic level of the enemy. Its special attack, on the other hand, scales with the player's magic level. Like other bows in the game, it fires Arrows.
This item is a reference to the coveted and expensive Twisted Bow from Old School RuneScape, which also scales damage based off of the enemies Magic level.
Where: [math]\displaystyle{ \left \lfloor x \right \rfloor }[/math] is the floor function.
Thus the minimum strength bonus is 111, and the minimum attack bonus is 102. The maximum bonus is obtained when fighting The Herald who has level 1600 magic. In this case the ranged strength bonus is 401, and the attack bonus is 280.