Yep, lot to lot variation is a reality of manufacturing life, and the reason the manuals say to always back off when there is any change in a load, and this includeds changes in lot numbers of brass, powder and primers.
I had extreme pressures show up one time with nothing more different then just lot to lot differences in some Remington 30/06 cases.
It doesn't take much to again run a few test loads for pressures once the "working up" has been completed and duly recorded along with your test targets.
As per RL22, I worked up loads for a 300 win. Mag. back a few years - Browning A-bolt w/26" tube - WW cases, CCI mag. LR primer and a 165gr Nosler partition.
That combination gave me between 3200 and 3300FPS, until I bought more powder. At which point my velocity dropped to +/- 3200fps.
You will read about this situation in the loading publications and about the only solution is to buy your components in larger amounts. You may not get one of the "fast" lots, but you will have consistancy which is more important then the extra 50 +/-fps.
Anyway, I normally tried to buy more then one can of powder at a time, once I had a load worked up and would ask for cans of the same lot numbers. Better yet, buy in the larger containers and then the issue won't come up very often.
Keep em coming!
CDOC