Unless you either have or go through the trouble of making a long throat in your chamber, I think that most folks find bullets heavier than 265 grains to be more than the case of the 38-55 will handle easily. I suspect that bullet is made for folks shooting 38-56's or 38-70's, cartridges based on the 45-70 and 45-90 respectively and having lots more capacity than the 38-55. Outside of that, I doubt there is a lot of call for a .379 bullet weighing 335 grains. Even if you were to ream the throat of your rifle, i'd be mighty surprised if you could break 1100 fps with that heavy a bullet and a charge of black weighing 48-52 grains, which is about all you could stuff in the case. Goex only shows 48 grains of black for a 250/255 grainer in their 38-55 data.
Edit, added this:
Most folks shooting the 38-55 are using smokless, either pistol powders making circa 900-1300 fps, IMR4198 for the high end of that range or are using 1680, 4198, 3031 or Reloder 7 for loads pushing 220-265 grain bullets at circa 1800 fps. A few are warming it up past that but then we are getting into 375 Winchester territory, and that's a whole 'nuther discussin'.
