Every size of stapler gets jammed at some point. If you are in a hurry or hold the stapler at the wrong angle, the staple can easily get caught in the stapler release hole on the head. Removing a jammed staple isn't very hard, but it does increase in difficulty with the size of the staples, and a heavy-duty stapler can have up to half-inch long staples. For these staplers, use needle-nosed pliers rather than tweezers, as you would on a small stapler.
Firmly grab the handle of the heavy-duty stapler. Pry open the staple release head (where heavy-duty staples usually jam) by placing the flathead screwdriver in the slit where the staples come out. Pry down on the screwdriver to pop the stapler head open.
Pull out the remaining good staple clip and set it aside.
Grab the jammed staple with the needle-nosed pliers and pull it out.
Insert the solid clip of staples back into the head of the stapler. Avoid putting single or small chunks of staple clips into the staple chamber, as these can become unaligned and jam your heavy-duty stapler.