There is a Legacy version
here.
Backpack BallistaItem 1Uncommon Source Guns & Gears pg. 62 2.0Price 18 gp;
Damage 1d12 P;
Bulk 2
Hands 1+;
Range 180 ft.;
Reload 1 minute
Type Ranged;
Category Martial;
Group Crossbow
This complex wooden device, worn on the back, contains a miniature ballista on a retractable arm. As an Interact action, you can pull a lever to deploy or retract the ballista. As long as it remains deployed, you must hold the ballista using that hand or some of the components spill out onto the ground, just like dropping any other weapon. While deployed, the device opens and raises the ballista up over your shoulder. While retracted, the ballista and its mount slide down and are concealed within the device. Although a backpack ballista packs a punch, the device is a challenge to operate. Reloading it takes 1 minute and can't be done while worn. As normal, you can't wear a backpack ballista with another backpack.
Traits
Uncommon: Something of uncommon rarity requires special training or comes from a particular culture or part of the world. Some character choices give access to uncommon options, and the GM can choose to allow access for anyone. Less is known about uncommon creatures than common creatures. They typically can't be summoned. The DC of Recall Knowledge checks related to these creature is increased by 2.
Critical Specialization Effects
Source Core Rulebook pg. 283 4.0Certain feats, class features, weapon runes, and other effects can grant you additional benefits when you make a Strike with certain weapons and get a critical success. This is called a critical specialization effect. The exact effect depends on which weapon group your weapon belongs to, as listed below. You can always decide not to add the critical specialization effect of your weapon.
Crossbow: The target takes 1d8
persistent bleed damage. You gain an item bonus to this bleed damage equal to the weapon's item bonus to attack rolls.