RE: Hornady Light Magnum rounds
Light Mags are loaded with very heavychargeand compressed powder at 64.5 grains for the 165 grain interbond. They should not exceed the stated SAMMI limit and work by maintaining the pressure levels for a longer time. For kicks I measured other factory loads and found most in 55-57 grain range. So it seems the Light Mags are using a 15% heavier charge of a slower burning powder than most factory ammo.
The above is for the 06 but apply to the other cases also I believe.