I have the 300BLK (the bootlegged Whisper) that I shoot in a rifle platform. I also have the .223 and the 6x45 that H20 noted.

The additional upside to the 6x45 for me is that 24 caliber gets it legal in Colorado for big game. As H20 noted, it is easy to reload as it uses .223 brass. It's a dandy antelope gun, low recoil, easy to shoot. I do not chase whitetail deer, but it would probably be excellent. I have shot it some at prairie dogs, and it works.

The 300Blk (Whisper) subsonic is kinda lousy on varmint size critters. It does kill, but it is not the spectacular results that you get with the small bores. And those big bullets skip and ricochet like crazy. At distance, you need a lot of scope adjustment. Without a can, it makes as much noise as any other handgun.

If I needed to shoot something feral or smaller, and I was worried about miss or ricochet, I'd probably grab one of my 17hmr's. They may not be the best choice for something like a coyote at 300 yards, but up closer the tipped bullets are really violent, hit or miss.

Craig