450 yards is easy with a decent optic, an accurate rifle that has the power to do the job, the right bullet (150 grain Nosler Ballistic Tip), and a working knowledge of how your rifle shoots at the given distance (
practice, not a ballistics program).
Heck, things don't get really complicated until you get past 600 yards...you don't need a heavy barreled 30-378 Weatherby to cleanly kill a deer at 600 yards. Even the 308 has PLENTY of power to do the job, I've taken deer at 800 yards with a 308...1 shot kills, dead within 50 yards.
I killed a coyote last week at 375 yards with a brand new 30-06 that I had only spent one day at the range with, with factory ammo...I spent 40 rounds firing at 300 yards, getting familiar with the trajectory and wind doping.
I put that bullet EXACTLY where I wanted it...right through the shoulder, just like I would have a deer.
EDIT TO ADD: The scope on this rifle is a Nikon ProStaff 3-9x40mm, its just a scope I had laying around...I'm gonna put a 4-12x on this rifle soon (not sure which flavor just yet)
I'm no professional shooter of any kind, I've never competed (except in "loser buys the beer" competitions) and I have no desire to...I'm just a guy that has enjoyed shooting at long range since he was a kid. I started out busting groundhogs with a 25-06 when I was about 13 and I will never forget the sense of accomplishment I felt when I finally connected with one at 500 yards...it took a lot of trial and error for me to figure it out back then. I didn't have the internet to tell me it couldn't be done...instead all I had was Jim Carmichael's "Book of the Rifle" which explained ballistics in a way that a simple minded country boy like me could understand.
With that book....and a lot of rounds fired...I figured it out (reading wind, understanding bullet flight, ballistic coefficients, etc.)
What I'm trying to say to the OP is this...Hitting a 6 inch target at 450 yards (or even 600) is fairly easy with LOTS of practice, an accurate rifle (does NOT have to be a heavy barrel), and enough common sense to know when to shoot and when not to...
If you're not positive that you can make the hit (due to wind, etc.)...don't pull the trigger!