:)A place I lived in Oregon years ago, Canby, had a local range. Before hunting season we alwys had these "site in" days.
The club had three chronos, generally two of them worked. We would set them up with rifle rests and a target and let guys shoot thru them. usually 3 rounds. In three years of helping with this and about 50-75 guns aday for 6 days. The VAST majority shot about the same less then the published specs as you listed.
Guns listed at 3100 shot 2900 2800, some less. the guns shown about 2200 or so (30-30) generally were closer, big pistol rounds were WAY off. Many a guy who thought he had a 3400fps WBY got a big surprise.
My hot dog, tried and true 7mm mag load, 160 grain, listed at 3150fps shot about 2950. boo hoo my 06 180 grain load listed at 2700 actually shot 2725 or so average!! It was a lot of fun and a real eye opener.
Carl