As noted above, it's a higher pressure round - 40,000 psi versus 36,000 psi for a .44 Mag, 35,000 for a hot hand loaded .45 Colt or a .357 Mag or 23.000 for a +P loaded .45 ACP. The smaller caliber also tend to produce a bit higher frequency than the 44s and 45s.
Accuracy wise, if the .30 ammo shot in a Blackhawk is tailored for a carbine length barrel using slower burning powders like H110, Win 296 or IMR-4227, the consistency in velocity will not be as great as it would be with rounds developed for use specifically in a 7 1/2" pistol.
I use the same powders in some .45 Colt loads, but the bore diameter and the resulting bore expansion ratio is much smaller for the .30 caliber round. Consequently, those powders are much less efficient in the available barrel length in .30 versus .45 caliber.
Finally, as noted above, Ruger (properly) head spaces rimless semi auto cartridges on the case mouth, and that does impose some limits on over all case length to ensure proper functioning as well as limitations on crimp in order to still provide enough case mouth for the bullet to properly headspace.