To find the volume of a rectangular pyramid that has the same base area and height as a rectangular prism, we can use the formulas for the volumes of both shapes.
The volume \( V \) of a rectangular prism is given by:
\[ V_{prism} = \text{Base Area} \times \text{Height} = 252 \text{ in}^3 \]
The volume \( V \) of a rectangular pyramid is given by:
\[ V_{pyramid} = \frac{1}{3} \times \text{Base Area} \times \text{Height} \]
Since the base and height of the pyramid are congruent to those of the prism, we can express the volume of the pyramid in terms of the volume of the prism:
\[ V_{pyramid} = \frac{1}{3} \times \text{Base Area} \times \text{Height} \]
Since \( \text{Base Area} \times \text{Height} = 252 \text{ in}^3 \), we can write:
\[ V_{pyramid} = \frac{1}{3} \times 252 \text{ in}^3 \]
Calculating this gives:
\[ V_{pyramid} = \frac{252}{3} \text{ in}^3 = 84 \text{ in}^3 \]
Thus, the volume of the pyramid is:
\[ \boxed{84} \text{ in}^3 \]