In the 1951 book "Woodchucks and Woodchuck Rifles", Landis describes shooting with a Highwall chambered for a wildcat .17 based on the R2 Lovell case.  This case has a reported 17 grain capacity with conventional coarse-grained IMR powders.  Landis says "the 16.0 grain charge of 4895 makes more report than the 15.0 grain loads with 3031 or 4320".  Bullets, cases & primers were apparently constants.  Only one rifle was used, so that also becomes a constant.  Apparently none of these loads were maximum for the rifle, as he later reports increasing his hunting load to 16.5 grains of 3031 or 17.0 grains of 4320.   

I know that .22 shorts go "pop" and 7mm Magnums hurt my ears, hearing protection or not, but why should the 4985 load be noticeably noisier than the other two?  Has anyone looked into the factors contributing to noise?

Also there is the ignition or deflagration of the less-thoroughly-combusted products of the slower powders outside the barrel, i.e., the muzzle blast.  Much the same effect occurs with a given load when the barrel is shortened, Magnaported or fitted with a muzzle brake.