One of the biggest advantages to reloading is you can make your ammo perfect for your rifle. You can seat your bullets the depth that is best. You can adjust the powder charge that is best. You can try different bullets, primers, powders, etc.
What good does having some guy you barely know load you some ammo gain you? And for such a common caliber as 300 WM which you can buy pretty much anywhere. The only good reason I can think of is to save money. Well there you go, you got blem bullets. I don't see where the gunsmith did anything wrong. Blem bullets usually shoot great. Make sure he at least sorted brass by headstamp.
I don't know a lot about long range hunting, and 500 yards is right at the threshold of being long range hunting. You are well beyond max point blank range, wind is a huge factor, accuracy has to be quite good. I wouldn't consider 1 MOA accuracy good enough, which is harder to achieve than most on the internet claim. I have no problem with long range hunting, but it is a specialized sport, using specialized rifles. It can be done with store bought ammo provided you find the one that shoots good enough. 300 WM isn't that hard to find, and if spending a few hundred dollars on ammo is too much, then you simply are not prepared to take a 500 yard shot, very few people are. That's the long and short of it. Get out there at 500 yards, take some shots, and see how it groups.