JWIII, I think your marksmanship ambitions are way beyond any practical use you might actually have for a, 'first rifle'. I've been shooting rifles for more than 50 years; and, I love the 300 Win Magnum! The 300 will reach out and, 'touch someone' better than 90% of whatever else is presently available below 40 + caliber; but - BUT - there is a price to pay! 30 caliber rifles can, also, be very punishing for the shooter to have to dial-in and practice with.
Personally, I honestly think you should learn how to walk before you run. I'm not going to brag on the internet; however, were you to ever see me put a rifle to my shoulder, the targets would speak for themselves. My first rifles were 22 long rifle caliber. From there I graduated to 22 magnum caliber in order to pickup another 25 yards of, 'dime busting' accuracy.
I was in my mid 20's before I became genuinely proficient with a 30-06 - Another, 'long range' rifle caliber that I have, also, learned to dearly love! (Fewer and less likely brass or chamber, 'problems' over other 30 caliber military cartridges!)
I don't know about you; but, the farthest I can shoot around my home is 300 yards. If I want to fire at 600 yards then I have to take an hour car ride to a distant range. In my experience it's a rare civilian rifleman who can work effectively with any rifle at 1,000 yards; and, those with whom I've shot who were good at it all used big complicated scopes and rifles with barrels that were as thick as fence posts!
If you want a word of advice from an old rifleman, I'd suggest you begin your studies of long range marksmanship with either a 243 Winchester, or 6mm Remington rifle.
If you don't reload, the 243 would be a better choice because the cartridges and brass are going to be easier and more plentiful to come by. If you do reload, then, I'd suggest going with the superior 6mm Remington chambering. Either caliber would be much more appropriate for you to begin with; and, I will say that after a lifetime of rifle shooting, I continue to prefer 6mm rifles; this is one caliber you'll always be able to put to good use and will, also, never outgrow.
If you would like to do some of this research for yourself, start by reading any of the various reloading manuals, like: Speer, Sierra, or Hornady. Any of them will give you an education in what to expect from a certain caliber and chambering. Me, personally? I'm not enough of a sadist to recommend that any young rifle shooter should begin his career with a centerfire 30 caliber rifle - especially with something as whopping as a 338!
(But, this is the internet; so ya never really know!)
One last thing: It ain't the gun; it's the shooter that really counts. An experienced rifleman knows how to make almost any rifle - in any chambering - work for him. Hand me a rifle, let me take 3 shots, and I'll either know how to use it properly at distance; or, else, I'll hand it back to you and say something like; 'No good!'
(I've done this many times! Usually, I'll make a friend; but, sometimes, you can also make an enemy, too. Like I said: It's the shooter and NOT the caliber or the gun.)