Re: Powder residue entire length of case....help
Disclaimer first - I am not a pro, so my experience is just that - practical experience. I will always defer to the pros. That being said:
I don't shoot 6.5-284. To get a frame of reference, I went and checked what virgin and fired brass I have on hand. I did some measuring (hornady headspace gauge also) and found:
300WSM, Winchester M70, Winchester cases, insert E
Unfired: 1.735" to 1.736"
Max spread: 3 thou.
22-250 rem, Cooper M54, Winchester Cases, insert B
Unfired: 1.561" to 1.563"
Max spread: 4 thou.
Based on that, the headspace change you are seeing is greater than the two different cartridges that I have on hand are showing. Excessive? I am flat-out not qualified to answer that. As you are using Redding dies, I would reccommend shooting them an email - my experience with their tech service has been great.
As an aside, I got into shooting/reloading 280AI a year or so ago. I was doing some research as Nosler standardized (through SAAMI) this chambering so they could market brass and ammo. I was considering buying some brass to save the effort of fire-forming. What I found is they had reduced headspace by 14 thou vs the original PO ackley design. Thus, their brass is 14 thou short in an original PO ackley chamber. Based on what I was reading, shooters/reloaders considered 14 thou "free" headspace excessive and a safety concern for case stretching / case head seperation. As a frame of reference you may want to Google it and see what they say as well.