'dave': What do you mean by "sleeve/sight"? Its sounds like you are describing the 1903 Springfield front-sight.
Many gun smiths (professional and amatuer) put the 1903 Springfield 'banded' front-sight on shortened Krag barrels to make 'sporters'.
Springfield Armory only did this in the 1920s on 22 inch barrels to make the so-called NRA or DCM 'carbine for public sale.