I'm with you, I'm guessing he bought the gun with a large quantity of ammo, it beat him up, and he got rid of it rather than trying to figure it out. Guns for sale on Gunbroker often have deals where you can buy a large quantity of ammo in the caliber rifle you are buying at a decent price; I'm guessing that's what he did.I'm guessing that the guy you got the rifle from wasn't into reloading, thus the large quantity of factory ammo that came with it!
He most likely couldn't hit the side of a barn with it either and that's why he sold it to you!
I would never purchase more than one box of factory ammo before testing for accuracy with any rifle; I do however shoot reloads in all my center fire rifles when hunting!
You may well have gotten a great rifle for a good price and I would encourage you to continue with tweaking your reloads until you find the one that shoots the way you like. Just don't let it beat you up too bad before you take a break!
I'm a little surprised that you tried so many things including messing with the beading before you addressed the ammo issue, that is where I always start!
Honestly, I was kinda surprised when I figured out it was the ammo/gun. I used to have a Browning Bar that was nearly a tackdriver without a BOSS. I figured the A Bolt should be more accurate, and with a BOSS, even better. And, I had a trusted Leupold that had been on several rifles without incident or question, so...
Hornady: I've had great luck with their ammo, and they have become one of my go-to ammos for most things that I use factory ammo for. I had really expected great things from this ammo/rifle combination.
I've been shooting rifles seriously (handloading, amateur bench shooting, etc) for 20 years now, and have NEVER seen a gun hate a factory ammo that badly. Even the SKS's I've owned and my Mini 14 will group better than that! It just had to be the rifle if it was shooting that badly. Then add the fact that normal 'deer ammo' that I buy locally runs $15-20 a box. and .338 WM runs $45 a box, plus shipping and handling, and isn't available locally. In my mind, it just had to be something out of sync with the rifle, or the scope went bad, or maybe it was me.
Eventually, this caused me to 1. Level and improve my shooting bench. 2. Work the kinks out of my midway shooting rest. 3. Load some good ammo. 4. Play with a BOSS for the first time, something I've wanted to do for years (yes, I like it, no, I don't care what it looks like). 5. Work on my recoil tolerance. 6. Wind up with a really great bear rifle, that will turn heads when someone asks what I'm shooting (haha). 7. Get a really great group, that I now consider one of my personal bests (lots of folks can shoot bughole groups with a 22 ppc, it's different getting a 5 round group with a 338!).
I'm really glad I kept at it, I've learned a lot from and had fun playing with this rifle. I'm looking forward to shooting it some more. I wonder if I could lighten it and still get good accuracy?!? Lol