I load 180 grain Berry's plated bullets and 180 grain cast bullets for my 38-40 Ruger Blackhawk. My loads are, by far, heavier than any 40 S&W load as these loads can only be loaded in a Ruger Blackhawk as opposed to any other standard 38-40. I will not push the plated bullets beyond 1200 fps but I can push the cast (and jacketed if I choose to do so) to much higher velocities.
As already has been stated, plated bullets can only be loaded to lead bullet velocities, that is around 1200 fps. Cast bullets and jacketed bullets can be loaded to much higher velocities, however, leading may or may not occur due to the hardness of the cast bullet. In order to keep the leading down with cast bullets, you probably want to stay in the range of 12 to 15 Brinnel hardness with 40 S&W loads. Don't be fooled into thinking that the harder the bullet, the less leading. The only downfall I have with the use of cast bullets is that they tend to be smokey and tend to leave a lot of soot on your gun. This is more than likely due to the waxy lubricant used on the cast bullet which is burned upon firing.
With reference to your shooting 40's from a carbine, I shoot cast bullets of roughly the same hardness as listed above from my 45 Colt carbines (up to velocities of approximately 1,700 fps) and rarely if ever get any leading from such cast bullets.