I have been big game hunting for over 58 years (I am 70 now), shot my first deer at 12 years old. Built my first custom rifle when I was about 20. I have always had a baseline accuracy requirement of minute of angle groups or better. If I can't get that, then something is wrong with my loads (I always have reloaded), my rifle or me! I learned everything by trial/error, reading early books/magazines and from my Dad. I just finished rebarreling my custom .300 WBY (comm. mauser action, B&C composite stock, Shilen SS match bbl) because it had gotten to the point that it would only do 2+ min groups. It now does <min gps out to 500 yds...my go to elk rifle. Topped with a 4x14 Leupold VXIII with a custom ballistic turret from Leupold.
Just set a goal of getting to min of angle groups and work towards it. If you buy a factory rifle, get one that is capable of that goal to start with. Learn the basics of good marksmanship (especially trigger control) and then get setup to reload. IMHO a reloader can always do better than factory loads. Every rifle will "like" one load better than another. Find it and use it. Practice, practice, practice! Muscle memory builds shooting profiency, along with the practice.
Lots of great advise in the prior posts. I would add a suggestion that helped develop the skills of my son in law who wanted to get into long range hunting. He had never hunted, but also did some 22 target shooting. Looks like you live in the Northeast. Since you have never hunted begin now using that 22, and doing some squirrel hunting. It is your scaled down long range rig. Using the same techniques and principles found on this site, your goal should be to put together a set- up that you can hit a 1" circle from 20 yards out to 100 yards. Head shots only. It isn't the same as big game hunting at long range, but it will definitely give you excellent basic training on the principles of both hunting, and precision shooting at extended ranges. A head shot on a squirrel with a 22LR in a 5 mph full value wind at 80 yards could be as tough as a lot of the long range shots on big game with a high power rifle.
"Let us speak courteously, deal fairly, and keep ourselves armed and ready"-T. Roosevelt
I often have buddies who are not long range shooters and have a variety of rifles from the old 30-06 passed down from dad, to modern utra mags ask me to help them shoot long range. The question at some point always ends up being "how far can I shoot with this set up?"
A simple test I use is to put an 8" target dot on my target stand. Using positions that they would use in the field we start shooting at 100 yards, move to 200, 300...... etc. The longest for that shooter is the last range he can keep ALL his shots in the 8" dot.
The only variable is what is considered a field shooting position. For someone who is shooting from a stationary box blind that may be off a bench with a sandbag for a rest. For someone doing a spot and stalk western hunt that may be a bipod and a bean bag.
You still have the variable of excitement in the equation, but if you know that you and your equipment are capable of putting ALL your shots into 8", you just have to work through the rest by making sure you are solid and steady or you don't take the shot.
Obviously, at very long ranges things can get a little more complicated, but I have found this to be a good method to bring some reality to someone's expectations. I often have guys come out that think they are going to be able to shoot 500 or 600 yards, but the holes in the paper tell the real story and they leave knowing 300 yards is their longest range without work on their skill level or an upgrade in equipment.
I want to thank all of you who responded. I fully realize that long range hunting requires a great deal of skill. I don't know if I will ever hunt at truly long range. That is why I framed my question in terms of MPBR for the 7mm-08 round. I appreciate all of the answers and advice. The 8" target dot at increasing yardages is a simple and excellent suggestion. I would absolutely use a rest of some sort or pass on the shot. I was thinking of shooting sticks, and if in a blind - a shooting bag. I have read a great deal of Chuck Hawks work and I agree with staying within the MPBR of the cartridge. Obviously you more experienced shooters/hunters are not limited by MPBR. I did mean to say 3MOA, not 3" because I want to be conservative. I am certainly working towards 1MOA accuracy. With the 22LR I can reliably shoot 2MOA at 100 yards, when my finances improve I will buy a centerfire rifle in .308 or 7mm-08. I assure all of you I will excercise sound judgement before shooting at any animal. Once I get my centerfire rifle, I will be ecsatic to try 300 yard any rifle/any sight matches. I might even try mid range prone at 600 yards. After many changes, I have settled on a Weatherby Vanguard Series 2 for about $500 and a fixed power Bushnell Elite 3200 for about $200. I think this will be a quality target shooting set up for $700. Need some 8" shoot-n-see targets. Thanks again fellas.