Well to be fair, deer and elk are a bit bigger than a milk jug. Basically the whole front half is a dead deer or elk, shoulder, high shoulder, lungs. So in my own opinion a deer is around 14" and elk are easily 20" Put the bullet in that chest area and you have a dead animal.
Also, it really depends on the conditions of the shot, whether you can get prone or not, the wind, among few other things.
There is no guarantee in hunting whether it's 100 yards or 1K. Look how many bow hunters wound animals at 20 and 30 yards. It's our job to try and make sure we do our part in knowing we can make the shot based on conditions and our own limitations. Use your own judgment and shooting skills to determine that. Joe Bob from the internet has no business telling anyone how far they should or shouldn't be shooting, based on their own skills, or lack there of.
All I know is give me my custom 15# hunting rifle in 7-300 Win Mag (and yes I do pack this rifle up and down canyons) with 180g ELDMs at 3100fps, up to 10 mph winds, laying prone with a bipod and rear bag/rest, there ain't no deer or elk alive that's walking away from me at 600, and thats guaranteed. I've killed a slew of deer, elk, bears, and coyotes from 300-1150 over the years. It's really not that hard if you know your rifle and limitations, along with the conditions. Sure I've missed a couple few times past 600, who doesn't, but even then, not very often. And it was always followed up by a quick 2nd shot that did the job. Being able to spot your own shots plays a huge factor in being able to quickly correct for a 2nd shot if needed.
I have a private 1400 yard range 15 minutes from my house. Steel set up from 300-1000 every 100 yards, also steel at 1200 and 1400 yards. Been shooting there for 25 years. Literally hundreds, if not a thousand rounds a year back in the day. 4-600 yards becomes a chip shot after a while. When your rifle has a confirmed dope chart every 100 yards out to 1200, handloaded ammo, not this junk factory precision hunter crap theyre shooting from 7# factory magnum rifles, a solid prone bipod/rear bag rest, it's really not that hard to make a 600 yard shot on deer or elk. Almost anyone can do it.
NF 5.5-22x, Swarovski 1500 rangefinder, kestrel, cosign angle indicator, scope level, harris 6-9" bipod, backpack for a rear bag, and Strelok Pro for a ballistics program is just part of the equipment I use. Rifle is a custom built Rem 700 in 7-300 Win Mag, 28" Bartlein Rem Varmint/9 twist with 4 port brake, 1.5# Timney, NF 5.5-22x in Leupold MK4 rings and 20 MOA base. Rifle weighs 15# and recoils less than a 223. Load is 72.5g H1000 with a 180g ELDM at 3100 fps. Rifle shoots under an inch at 300, and 4-6" at 1K any day of the week.
And also, just because you're in the military or marines, doesn't mean you know Jack, or can shoot worth a shit. That's a huge common misconception in todays society. Unless you're a sniper in the military, they literally don't teach you shit in how to shoot, and definitely dont cover any long range aspects. They cover the basics and that's it. Your qualifying open sighted AR15 does not need apply here Rambo.
Anyway, that's my take on the whole situation. Call it what you want, but there are a lot more guys who can shoot 600+ then you think given the right conditions, equipment, and skill level. And I have nothing to prove to anyone. My dinner table speaks for itself the last 25 years, with elk and deer on it every year.