The process I believe is referred to as "particle erosion", and is most pronounced in the area of the bore immediately ahead of the throat due to higher heat and pressure as the bullet starts to move down the bore. Ball powders generally develop pressure at a lower flame temperature than extruded powders, hence less throat erosion. In the test done a number of years ago by the American Rifleman, the increase in useful barrel life was something like 15 - 20% more in the .308 Winchester if I recall correctly. May not be as much in the .300 Ultra Mag class of cartridge.

Another similar phenomenon is the shorter barrel life one experiences with heavier bullets. I have two .243 Winchesters - both with Krieger barrels - and cut with the same reamer. One has a 12" twist and is used for varmint hunting with mostly 70 grain Nosler Ballistic Tips. The other has an 8" twist and is used exclusively for long range target shooting with various VLD bullets in the 105 to 107 grain range. The 12" twist gun has about 3,000 rounds through it - and shows less throat erosion (through the Hawkeye bore scope) than the 8" twist gun that has less than 2,000 rounds. Reason??

Even though the heavier bullets use less powder to reach full throttle velocities, and the full throttle velocities are lower; the heavier bullet takes longer to get moving down the barrel; exposing the area just ahead of the throat to the forces of particle erosion for a longer period of time.