I remember reading or hearing that for gas powered semi-autos you should expect muzzle velocity to be 100fps slower than published velocities. Is that correct? Specifically, I'm talking about a Remington 742 in 30/06 (22" barrel). The factory loads state 2810fps as the muzzle velocity but I'm thinking that I might as well subtract 100fps due to the semi-auto action plus another 50-100fps since the claimed velocity is probably high (based on a 24-26" barrel, perfect temperature, and just a liberal claim in general). Does that sound about right?

I would say 100 - 150 fps is a safe drop in velocity. Thats what I see with a 22" 7400.

Bigcountry, have you actually chronographed this drop in velocity against the same load in another rifle? I have heard that the difference in muzzle velocity between semiautos and bolt guns is negligable, all other things being equal (barrel length, ammunition, etc.)

I'veheard conflicting stories on this but have never actually attempted to measure the differences myself.

Anyone have any hard evidence out there one way or the other?