jwall,
Faster or slower velocities than expected are common in rifles chambered for some old military cartridges, especially European rounds, because throat length varies considerably. The original military throat lengths for the 6.5x55 and 7x57, for instance, were designed around very long round-nosed bullets, while some (but not all) modern sporters have much shorter throats. The 8x57 can also vary: While the original chamber had a very long throat for the typical heavy roundnoses, it was eventually shortened for the later light spitzer load--but some later civilian sporters also had longer throats, because in the early days of soft-nose cup-and-cores many hunters preferred long, heavy bullets for their superior penetration. I have just such a German sporter with all the usual touches such as double-set triggers, slim stock with side-panels and Schnabel forend, etc, and its throat is long enough to swallow 250-grain Woodleighs Weldcores with no trouble.
But even modern rifles can have slightly varying throats, or bore dimension. I've handloaded for more than a dozen .270 Winchesters, and the same loads would produce anywhere from 2900 to 3100 fps with 130-grain bullets and various appropriate powders such as IMR4350 and RL-22. If I ran into a slightly "slow" barrel that wouldn't get 3000+ fps with a 130, I added more powder to get there, and never have run into apparent pressure problems--even in a couple of rifles with 20-21" barrels. However, have also loaded for a couple of .270's that got 3100 fps with listed data, and since I didn't see the need to go for more, I quit there--unlike some handloaders who think any load that's apparently "safe" during one test will always be safe in all conditions.
One of the reasons I use a chronograph when working up loads is that, like Denton and the Sierra tech, I've also been told by more than one pressure-lab tech that adding a little powder to loads that produce lower velocities in a given rifle is a safe, as long as velocity was within "normal" boundaries.
