The .45-70 Gov’t and .450 Bushmaster are both called straight-walled cartridges. There is no taper toward the bullet, shoulder, neck, or other changes of direction in the case walls. There’s been a resurgence of interest in both because a number of states have now made the use of this style ammunition legal during big-game seasons (check local regulations).
The physical dimensions of each cartridge are far from identical, despite the resemblance. Case length in the Bushmaster is 1.7 inch, and the .45-70’s runs 2.105 inches. Also, the latter has a rimmed case and the former has a rebated rim—noticeable groove or slimming of the diameter above it.
There are other differences, but it all adds up to the fact that no gun can run both cartridges interchangeably. Standardized specifications from the Sporting Arms and Ammunition Manufacturers’ Institute prevent accidentally chambering the wrong ammunition.
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45-70 VS 450 Bushmaster Advantages
That fact’s critical because the projectile diameter isn’t even identical between the cartridges, despite names that hint they are. Bullets for the .45-70 Gov’t measure .458 inch in diameter. This girth gives the elder statesman a decided advantage when it comes to loads available that improve the chances of delivering an ethical, one-shot stop during hunting seasons. Additionally, there are many different bullet weights and styles in that width.