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No reason why you couldn't. However, Wikipedia says that the .50-140 bullet is .512, while .50 BMG bullets will be .510. However, provided your barrel is .510 groove and you are able to load the very long BMG bullets, you shouldn't have any issues.
Considering the twist rate was designed around (relatively) short lead cast bullets, I predict less than spectacular results. But giv'er, and let us know if it worked.