I've seen and shot some rifles with a sharp, rapid taper from the last 1/2 inch or so to the muzzle so that the actual muzzle is very slim. The thinking is that this reduces the muzzle area against which the exiting gases can push.
Whether this is what really happens, I can't say, since I've never had two otherwise identical rifle/bullet/load combinations to compare at any one range visit.
Sounds good though... :shock:
(Think this would qualify as a 'hunting style' bbl taper?) :-D