Chronographs sure are eye openers. I have a Oehler 35P.
Lots of guys have asked me over the past 18 years or so if they can run their ammo thru it. I always say yes.
However, most of them went away very angry, sometimes even telling me my machine was screwed up. Nobody wants to believe that their pet rifle load, whether store bought or hand rolled, is 200-300 feet per second slower than they were led to believe.
In my experience, only my .300 Weatherby rifle makes "book" velocities routinely. In handguns, my Kimbers in .45 ACP come awfully close, usually +/- 25 fps. The four inch ProCarry is usually about 50 fps slower than the five inch Eclipse.
I have had two instances where I was way over book value. The first time was with .44 magnum. The book said that I should have gotten 1200 fps when, in fact, I got 1700. Scared me so bad I took the remaining loads apart and checked them all. I found nothing wrong, but I did not use that load again.
The second instance was with my Model 70 Featherweight in .280 Remington (7mm Express). With 160 grain Nosler Partitions I was getting 2880fps. The absolute best deer killing load that I have ever developed. I was afraid to duplicate it again, though.
Just last week I discovered something that I thought was a bit odd. I have always used 59 grains of IMR 4350 under a Sierra 150 grain bullet for my 30'06 deer hunting loads. They usually clocked at 2800+/- fps. The loads that I rolled last week clocked at 2950 fps. Did something change with IMR 4350?