...may be longer than you think:
I received a direct answer on the estimated maximum danger range of rifled slug, sabot slug, .44 magnum and 45-70 rounds from Winchester Ammunition:
X12RS15- Rifled Slug, 1 ounce @ 1600 fps: 1,068 Yards
X44MHSP2- .44 Mag. 240 gr. @ 1760 fps: 2,239 Yards
X4570H- .45-70 300 gr. @ 1880 fps: 2,291 Yards
SSP12- 12Ga. 385 gr. @ 1900 fps: 2,971 Yards
The Winchester Tech. recommended adding 200 to 300 additional yards to allow for velocity variations, temperature, wind conditions, etc.