Re: How do I get my extreme deviation or spread DOWN?
I did a lot a work on perfecting ES in my 6.5x284's. The basic case prep and components are 140 Hunting Berger VLDs, or 142 JLK's which perform identically, the only difference a .612 vs .640 BC. I use Lapua brass and neck size with.292 Reddng bushing dyes, neck sized, head-spaced .002"under fired brass length. I'll body size and anneal every 4-5 firings. Runout is less than .002". For all components, I always use the same lot. For a few rifles I have set up, the above is my base. Once I get good accuracy, .25-.5MOA at 200 yards, I then chronograph for velocity and ES. My goal with the 140's is to get velocity in excess of 2950 and ES of under 10-12 FPS for 5 shots and repaeatable over different days.
For optimizing ES and velocity the single biggest variable is getting good chronograph data. I have used several brands including an Oehler 35 and set-up and lighting have to be dead nuts repeatable. For me this has been the biggest source of false ES.Note: (IMO, greatest contribution to getting readings easily and accurately is the recently introduced Magnetospeed. Since using this I have elimated this variable for me!)
With my rifles I have found ES to be effected by:
Primer type and brand.
Seating depth. There are different accuracy and ES nodes with VLD's. I have found good accuracy "and" ES more often at .050-.1" off the lands.
I only change one at a time. My go to powder for hunting loads is Retumbo. I'll start with charge weight for velocity, ES, and accuracy with .075" off the lands, and try to optimize first varying seating depth. If this doesnt get me there, I'll try different primers. I start with Fed215's, but will try CCI mag, Fed210's is a last choice, but you will loose 50 fPS velocity. I had one rifle that needed a powder change to H4831sc to get then results I wanted. This is the process that I follow, but will have to say that the it's not as bad as it looks. The last two rifles I worked with got there with 57.5 gr. of Retumbo, 215's, and a seating depth of .075" off the lands. 2970FPS, ES 11, sub .5MOA. I only played with seating depth and charge. I think this is a good starting point.
"Let us speak courteously, deal fairly, and keep ourselves armed and ready"-T. Roosevelt