I honestly don't see the benefit of the 458 over the 450 Bushmaster for deer. The Bushmaster already sprays about 10lbs out the other side. Only real benefit is not having to size the 500gr 45-70 bullets for subs.
Both are good calibers however, I feel that the 458 has a bit more options. The 450 can use .451-.452 diameter bullets. Those are 45 ACP and 45 LC diameters. Those bullets are not ideal for. rifle velocities. There are .451-.452 diameter bullets that are meant for rifle velocities but they tend to be more expensive. The .458 diameter bullets have been around for literally over a century. The selection and variety is more in favor of the 458. Furthermore, the cost is considerably less.
For deer, either will work great. For me, I am out west and I have the opportunity to hunt much larger critters. I want a tough bullet that will not break the bank and be able to put an elk, feral cow, big mule deer, or hog on the ground. Hard cast bullets meant to be used at rifle velocities are an economical choice that I did not find for the 450.
Lastly, I did fire the 450 and 458 in both bolt and AR platforms. Over a wide variety of commercial and hand made loads, my experience is that the 458 is more accurate than the 450. For me, I am an accuracy snob. This was my thought process when I chose the 458 over the 450 and 50 Beowulf.
