Lugerstew,
How did you load and transport the ammunition? Same orientation during the trip, or might it have been upright the first time and on its side the second time? Long ago one of Precision Shooting's authors had a load that shot great when he loaded it at home, but that gave him sticky bolt lift when he loaded it at the bench on the range. He finally figured out the vibration of being carried and driven and carried some more at the range was settling the powder. With stick powders, settling can decrease burn rate by making it harder for the flame front to move between the grains. How much effect this has varies with the particular powder. This is one advantage compressed loads of stick powders have; they tend to lock the powder in place so vibration doesn't pack it down any. The Federal GM308M load is an example, and its reputation for consistency is very good. I would expect cartridges transported on their sides to pack less than those transported upright.
A second orientation factor, if your loads are not compressed, is the powder position at firing. Years ago I had occasion to shoot some 1964 National Match ammunition in several club Garands and intentionally tipped them either down or up before leveling the guns to fire them over my chronograph. The charge of IMR4895 in those old loads only filled the cases about 82%, so the powder shift was significant. Powder forward and away from the flash hole shot 80 fps slower than powder back over the flash hole, and powder forward produced nice rounded primers while powder back gave a fairly flat primer. So powder position can matter to pressure reached, too. If you kept your ammo in a box nose-down for the first loads and nose-up for the second set, that might encourage a similar effect.
Keep in mind the Hodgdon data is for their guns with their component lots. They have a ±3% tolerance for the burn rate of their extreme line of powder, and yours could be at the faster end. (Were you using the same lot of powder in both instances?) They use Winchester cases most of the time, which, in most chamberings, tend to be on the large end of the capacity range; i.e., larger than Starline, Remington, Federal and most others except sometimes Hornady. So if you don't use Winchester cases, that can be the issue. I note, too, that Winchester has changed a bit over time, with their .308 Win cases weighing more now (around 166 grains) than they did fifteen years ago (around 156 grains), so old data in Hodgdon's charts may err on the high side. They often use a Winchester or a Federal primer. Federal standard primers are among the mildest, while their magnum primers are among the hottest, so if you substitute a Federal magnum primer for about anything else, including Hodgdon data with a Winchester primer, you may raise pressure some (this varies with a number of other factors).
