rcamuglia,
I would contact Hodgdon and tell them your H4350 experience. Your lot of powder might be defective.
I've talked to a few powder manufacturers, and while they won't tell any journalist everything (for obvious reasons in a very competitive business), but they have admitted that lot-to-lot uniformity of any powder is difficult, mostly due to differences in atmospheric moisture.
My last test with H4350 was with a 7x57 and 140-grain bullets. I run my cold-change tests by chronographing on different days, one as close to 70 as possible and the other as close to zero as possible. The rifle and ammo are at the same temperature as the air (for the cold tests I leave them in an unheated garage overnight), and the same chronograph is used. I also run point-of-impact tests at the same time. At 70 degrees the load chronographed 2842 fps, at zero 2834, which is as little (or even less) variation than usually occurs between shot strings on the same day.
That test just confirmed a LOT of chronographing of H4350 loads I've done in varying conditions over the years. I certainly wouldn't expect the difference you encountered, which is why I suggest contacting Hodgdon.
Another great reason to buy powder by the 8# keg...
