The Pancor Jackhammer is a weapon featured throughout the Thing-Thing series, as well as the Thing-Thing Arena side-series.
The Pancor Jackhammer is a prototype full-auto shotgun designed by John A. Anderson of the New Mexico-based Pancor Industries in 1984, and was patented three years later. It could fire 12 gauge shotshells at a rate of 240 rounds per minute, making it quite a potent weapon.
In Thing-Thing Arena 1 and Thing-Thing Arena 3, the ammo for the weapon is gun-specific, meaning that you'll have to grab other Jackhammers from the enemies in order to replenish your supply, and it can be scarce at times. The reload time for the Jackhammer in Thing-Thing Arena 3 is rather slow, so being patient is key.
While the Jackhammer is a powerful weapon, it's best used at close range, like any other shotgun featured throughout the series.