Need Recommendation For A Heavy Car

I own several Atlas TOFC cars like the one shown in your link.  They are the heaviest cars I own, but I have no way of weighing them to any degree of accuracy.

A K-Line diecast 4-bay hopper filled with lead shot (from the gun store, for shotgun reloading) would tip the scales around 10 pounds.

if you're not looking specifically for a flat car, Atlas Berwick Hy-Cubes are very heavy.

For heavy cars the MTH Premier gondola with junk load is quite heave howver all of the weight is in the junk load. K-line made some die-cast flat cars with 4 trucks that can be fairly heavy, these can be tough to find. K-line also made the diecast hopper cars that are so heavy they may limit the length of you trains to just a few cars.

K-line diecast Hoppers Doug W. has 15 of them.

You want heavy, like grj says k-line for cast hoppers are the heaviest. Want more detail, then the Atlas O die cast hoppers.

Those cars are pretty heavy. The K-Line die cast flats with multiple trucks heavy as well.

Got rid of the K-Line die cast hoppers, too heavy:-)

The Atlas PS-2 hoppers are fairly heavy.

What is your goal? The guys have good recommendations here.