Castle Rock,
I had the same experience a number of times after buying my first chronograph. They were very rare back then, and every guy who asked me to check the velocity of their loads was disappointed (and as you noted, often somewhat angry). But I doubt the loads used were the issue, or are today.
Instead the problem is a common condition called Velocity Optimism. Those who refuse to spend a hundred bucks on a basic chronograph instead check several sources of data for their approximate load, then pick the source listing the highest muzzle velocity--even if the data used a different bullet make, primer or barrel length than they're using. All they care about is whether the powder and bullet weight are the same.
This method of velocity estimating is bound to fail, because test barrels that provide the highest velocity normally do so because the chambers and bores are usually tighter than the average factory rifle, so tend to provide higher velocities for the same charge.
Some companies use test barrels for determining pressures, then chronograph the loads in what they sometimes call "typical" factory rifles. But there is no such thing, since factory chambers and barrels vary from pretty tight to very loose. But Velocity Optimists, by definition, don't pick speeds from loose-barreled factory rifles.
