This would fall under negligent tort. Tom did not secure his weapon to protect humans. The gun should have had some kind of safety feature enabled or been locked in a safe. 

Tom could say Gary was trespassing on his land and had trespassing signs however, it is late and dark. Does Tom have any automatic lighting? If not, Gary would have no way to see the signs posted. 

Another defense of Tom's could be breaking and entering. However, I would defend this with premeditated murder or violence. Having the shotgun,  loaded, hanging by the front door would suggest he was waiting for someone to come and he would kill or injure them.

There are 4 elements of negligence, Duty of Care, Breach of Duty, Causation and Damages. Tom failed to maintain the duty of care in his home. As a gun owner, Tom has the responsibility to maintain the health, safety, and well-being of others. This would mean keeping his gun in a secure location, with safety on and nothing in the chamber. He also had a breach of duty which is when a person's conduct fails to meet an applicable standard of care. Similarly to the duty of care, Tom did not uphold an appropriate standard of care as a gun owner. The causation was the loaded gun. The damages were the sustained injuries from the shotgun firing. 

Upon first reading this, I did not think Gary would stand a chance in this lawsuit. Reading about negligence changed my mind. I now believe Gary would have a decent chance of winning this case.

What would be a good response to a discussion like this?