The 450 Bushmaster is a large-bore straight-walled centerfire rifle cartridge designed to deliver heavy-hitting performance from the AR-15 platform. Popular for big-game hunting and in straight-wall-cartridge hunting regions, it pairs a large .452-caliber bullet with short-to-moderate-range power.

The 450 Bushmaster traces to the "Thumper" concept — the idea of a large-bore cartridge that could deliver a heavy, hard-hitting bullet from the AR-15 platform for effective single-shot stopping power on game. Introduced commercially in the mid-2000s, it answered that goal with a big .452-caliber bullet in a cartridge that functions in modified AR-15 rifles using standard-size magazines. Ballistically the 450 Bushmaster fires a large, heavy bullet — commonly around 250 to 260 grains — at moderate velocity, delivering substantial energy at short-to-moderate range with the characteristic heavy-bullet performance of a big bore. Its trajectory drops off at distance, so it is fundamentally a close-to-moderate-range cartridge, well matched to the ranges typical of much big-game hunting. It found a particularly strong role in the Midwestern states that restrict rifle deer hunting to straight-walled cartridges, where its power and AR-15 compatibility made it a popular choice well before purpose-built rounds like the 350 Legend arrived. Its recoil is notable, in keeping with the heavy bullet and energy. Today the 450 Bushmaster is used for big-game hunting — especially deer in straight-wall-cartridge regions — and recreational shooting, with solid availability in AR-15 and bolt-action rifles. Its combination of large-bore power, short-range effectiveness, and AR-15 compatibility is why it became a leading heavy-hitting option for the platform.

General information about this caliber — not a recommendation for this specific firearm.