You need to post more data: How far? What is the target? Where are you hunting (both long and short shots or more one sided)?
Good news: Lots of quality ammo for 300 WinMag.
Factory stuff I would look at: Nosler and Barnes factory ammo with their bullets. Barnes 150gr TTSX is pretty flat shooting and will work up to elk. Not my first choice for elk but it works. Nosler turns out some of the best stuff out there. 200gr Partition from the 300 WinMag will hammer an elk.
If your shots are going to be < 600yds then factory ammo will cover it. But if you stretch that pretty much you're going to be told to start reloading.
Two things you need right away is a quality laser range finder and a chronograph. The range finder is standard equipment these days and rightly so. The chronograph comes before any reloading equipment (in my book) because you need to know the velocity of your ammo to dial in the ballistics programs. There are a ton of good free Ballistic programs on the web. Chronographs are available on sale for less than $100. Absolutely no reason for hunters not to own a chronograph these days!
FYI: I have never had factory ammo deliver the exact velocity they claim. Mostly less, some A LOT less, can't remember any shooting faster. I've owned a chronograph since the first Shooting Chrony. The one when there was only one model and it didn't have a memory or calculator. Used a notepad to record velocities and did ES & SD when I got home to the calculator. This was before PC's.
It was the best investment I ever made! And they cost less today!