If it is a used pistol, and likely is, it might be full of old, gummy oil and dirt. That will certainly make for a horrendous trigger pull. I'd recommend a good cleaning and light lubrication. If you do strip the pistol, inspect for damage and gently smooth any roughly machined spots or burs. It would also be a good idea to install new springs. These are service weapons, not target pistols, so I would recommend using factory springs or aftermarket springs that duplicate factory specs.

How heavy should the pull be? In general, double action pull of about 12 pounds and a single action pull around 6 pounds seems to be normal. My 439 does have a slight amount of rougness in the double action pull and the pull gets progressively heavier as the hammer draws towards its full cocked position, this is normal to the design. The single action pull is longer than that of a 1911 and has just a hint of roughness in it.