The volume \( V \) of a rectangular prism can be calculated using the formula:
\[ V = \text{length} \times \text{width} \times \text{height} \]
For a rectangular pyramid, the volume is given by the formula:
\[ V = \frac{1}{3} \times \text{base area} \times \text{height} \]
If the pyramid has a base and height that are congruent to the prism, its base area is the same as the base area of the prism.
Let \( B \) denote the base area of the prism (which is the same for the pyramid), and let \( h \) denote the height of both the prism and the pyramid. The volume of the prism is given as:
\[ V_{prism} = B \times h = 252 , \text{in}^3 \]
The volume of the pyramid can then be calculated as:
\[ V_{pyramid} = \frac{1}{3} \times B \times h \]
Substituting \( B \times h \) with 252 in the pyramid's volume formula gives:
\[ V_{pyramid} = \frac{1}{3} \times 252 = 84 , \text{in}^3 \]
So, the volume of the pyramid is:
\[ \boxed{84} , \text{in}^3 \]