I have all the respect in the world for Rocky's expertise. That being said, I have compared Browning BAR's in 25-06 and 280 to bolt guns by shooting the same the loads side by side over a chrony.
Chrony said the BAR was shooting the same loads ~ 200 fps slower.
I believe Browning has publicly admitted the same.
Of course the 200 fps only matters to the chrony. Neither the operator nor the intended critter will notice a practical difference without reading the chrony.
GE
My results are the same as yours, every time that I have chronographed a semi auto of the same caliber and barrel lenght as one of my bolt actioned rifles the velocity has always benn lower in the semi auto... by as much as 200 FPS..
A lot a semi's have chambers that are even sloppier than factory bolt guns, and therein lays your difference.
I've seen 270+fps difference between chambers, and they were both cut in the same barrel, mounted on the same receiver, and using the same lot of handloads. At 26" with a oversize throat the ammo was chron'ed at 2725, at 25" with a tight throat the same ammo chron'ed at 2995
