Well, I did a little more digging and found some interesting info with regard to the "barrel stretcher" that was referenced with the Atkinson barrel.
Apparently, the 'stretcher' is in fact an aluminum sleeve. If you will think of a carbon fiber wrapped barrel. The original barrel was turned to a very slender contour and supposedly threaded at the muzzle. The stretcher, an aluminum sleeve with internal dimensions very close to the exterior dimensions of the barrel was slid over the original barrel and a barrel nut (think muzzle protector) was threaded on the muzzle. When drawn tight the barrel nut had the effect of 'straightening' the barrel, decreasing the weight of the barrel, and increasing the heat dissipation of the barrel.
So the story goes.
Some of our BR guys fooled with tension-ed barrels for HV and unlimited rifles where weight wasn't quite the problem. The purpose of putting a tension on the barrel was an experiment to reduce harmonics in the barrels. A lot of work went into them, but I haven't seen any in several years. Some even filled the space with antifreeze.
