Well, I can only find 3 weights of 8mm bb, they are .27 .34 .48 (I guess there is many more, I just cant seem to find em)
So, they will need to chrono at the following to be legal (under 1j)
.27 @ 280FPS = 0.98J
.34 @ 245FPS = 0.99J
.48 @ 210FPS = 0.98J
Hope this helps.
EDIT: Thought id also throw in the links for the BBs mentioned above.
Click here for .27 BBs
Click here for .34 BBs
Click here for .48 BBs
Edit:.....Again.
Just noticed on the Redwold website for the pistol, they list it as shooting at 250fps. So he should be just fine