Re: Powder Lots...
The bottle I get my powder in are nearly always big enough to hold twice the original fill. If I buy two pounds of powder and it's two different LOTs I MIX them together to form one NEW LOT. I do a thorough mix, rolling and tumbling the bottle to ensure things are well mixed. There are powders that are better known for being very different LOT to LOT, Reloader 25 and 22 come to mind...be careful with your new Custom Mixed LOT and work up the loads.
If you can find some VV bottles they are really big or the Reloder bottles are extra large to. REMOVE the original powder label if you're going to mix powders in any bottle not the original. Mix the powders (tumble and roll in the "mixer bottle" and pour the NEW LOT back into the original properly marked bottles, line through the LOT numbers so you will remember that you've MIXED the LOT but maintian the ability to see the original LOT number in case there's a recall (you'll lose the entire mixed LOT on a recall).
The vertical stringing for me is caused when I don't position my shoulder in the same place on the butt of the rifle, a little too much high (heel) or too much low (toe) and the recoil will be effected. There's a great deal of data in some early posts on this site about shoulder pressure, heel and toe and all other variables when shooting from a bipod, try a search.
Bond-ese, James Bond, 007 "Shaken, not stirred!"