The bore (diameter across the lands) is .450". The groove diameter is .458". And those are just the ideal numbers for conventional rifling in .45-70. You need to slug the bore with a pure lead slug and use an OD thimble micrometer with ten thousandths resolution to measure these two for yourself to know it for certain. When you have the real groove impression OD you can choose the sizing die to size your cast bullets 0.001" to 0.002" larger. Thus, if your bore is dead on (not all that uncommon these days), your cast bullets will be sized 0.459" to 0.460".