Ok, I went to the BB website. PDX didn't specify a bullet weight, but I'll guess the 125gr.
It is "lighter" than BB's HEAVY .357 , but comparing their 4in bbl vels to typical vel claims using 4in vented test bbls it is similar to normal full power 125s . So to simulate the recoil for practice, use whatever inexpensive 125 at hand.

For slightly less recoil try Winchester White Box 110gr.