The original casting was made from a mold taken from an original made usually out of clay or wax. The inside of the mold will hold exactly the same volume as the original sculpture. During the casting process melted wax is poured into the rubber mold. The wax is at its most expanded state when it is melted and at that point it is exactly the same size as the original sculpture. However, as the wax cools, it shrinks and pulls away from the mold. When it solidifies and is at room temperature the wax version of the sculpture is a little smaller than the original clay or wax sculpture.
The next step is to cover the wax with a ceramic shell that doesn't expand or contract. (If it does, it's a very small amount) The shell is put in a kiln and the wax is burned out leaving a hollow shell. Molten bronze, at it's most expanded state, is then poured into the ceramic shell. As the bronze cools, it begins to shrink. The shell usually cracks as the bronze pulls away from the inside of the ceramic shell. Now the bronze version of the sculpture is smaller than the wax version was.
Because there was shrinking in both the wax and the bronze stage, the final casting is noticeably smaller than the original clay or wax sculpture. There is also a small amount of distortion. When a re-cast is made, a rubber mold is taken from an existing bronze casting and goes through the same stages as the original casting so it ends up being noticeably smaller than the bronze the mold was taken from.
Since an original Remington or Rodin bronze would cost millions, a re-cast would be a good alternative. Unfortunately, first generation re-casts are rare. What you see in stores are probably many generations from the first re-cast. A person getting in the business of making re-casts needs a sculpture to make a mold from so where do you suppose he gets it? Not a museum, he gets it from a company who sells re-casts, who got their casting from another company who got theirs form someone else, who.... As a result, what you could be seeing in a store or on the internet could be a re-cast of a re-cast of a re-cast of a re-cast of a re-cast... They are not only smaller the distortion is multiplied as well.