Re: Extreme spread
I am afraid that at this point, you have to enter into the process of elimination to find the culprit.
Brass, bullets, powders, seating depths, primers and so on. You might need a total load overhaul, and even then it might not fix. I had a .220 swift that shot 1/4" groups at 100 yards all the time, but I could never ever get the sd down below 20. I tried every trick in the book and no luck. I did proceed to kill chucks out to 700 yards though so I guess it wasn't too bad. But I know what you're going through and it is frustrating. Keep us up to date on your experiments!
If it's not far, it's boring.