New reloader need powder advice

[Jack]

ApacheHunter, welcome to Huntchat!
I can tell you've been doing your homework- 4350 and Reloder 19 are among the first few powders I'd reach for if I were doing some load work up for the 280 with 140's. Another good choice would be 4831, if those 2 powders don't work out.
Very wise of you to check several manuals- every company uses a different test firearms- and they do sometimes show different results.
Now the bad news ...which powder is best? No one knows which powder will work best in your firearm. Only your rifle can tell you that. Firearms, like people, have personal preferences.
Here's what I did when I worked up loads for my 280: I tested both IMR-4350 and Reloader 19 with Nosler 140 Ballistic Tip bullets. The best 4350 load was a bit faster than the best Reloder 19 load, but the Reloder 19 load was surprisingly accurate, so I've been using Reloader 19 ever since.
In the more bad news department the loads that work well in my rifle won't tell you much about what will work well in your rifle. The only way to know for sure is do your load work up, go to the range, and let the rifle tell you what it likes.
Good luck!