I'm pretty certain that's mostly a myth. From what I've read on this subject, practically all the powder is burned within the first few inches of the rifle bore.The hot gases continue to expand, however, andso the bullet continues to accelerate until it leaves the muzzle. A26 inch barrelwill yield more velocity than a comparable 24 inch barrel.

My 7mm mag Sako 75 has a 24" barrel and while I may not be getting the velocity a 26" barrel would produce, I get all I need.

As far as the 7mm mag vs. .30-06 thing is concerned, I'd have to say the difference is barelyworth talking about. Over the years I've owned more rifles chambered for the7mm mag (5) than any other cartridge and I can't remember seeing them do anything that couldn't also be done with a .30-06. I like em' both.