Blastfighter (1984)

The hero of the film is a murderer. He is an ex cop who served eight years in prison for the murder of his wife's murderer. Upon release from prison, he decided to return to his hometown to escape from his past. En route to his ancestral home in Georgia, one of his friends gives him a gun that fires grenades, smoke bombs, steel balls, rockets, and several other types of projectiles. One day, while just looking through the scope of his gun for no apparent reason, he happens to spot a large buck. He follows the deer with the scope and is surprised when he witnesses a group of local boys poach the deer. The hero puts the gun under the floorboards of the porch, where it remains until very near the end of the movie. Upon investigating the poaching, he uncovers a horrifying poaching ring run by a man from Hong Kong who is paying the locals a couple of thousand dollars per deer and using bits of the animals for Oriental medicines...