For those that take the Precision Shooting magazine, Bill Calfee, 22LR BR gunsmith of the GURU level has been writing a series of articles on that subject over the last year or so.
He talks about busting old myths on barrel dimensions and what makes a truly shooter barrel. Bottom line is that he is a strong advocate (understatment) of the requirement to "slug" barrels with lead slugs to determine high and low spots and that the muzzle absolutely must be tighter than the rest of the bore. With the slugs he determines the exact spot for the muzzle regardless of blank length for pure accuracy.
As for a reverse taper, think of the blunderbuss. Not exactly known for precision accuracy. Now that is an extreme example, but perfectly appropriate.
That is also the major reason after mftr lapping rarely works and often hurts the barrel accuracy. The lead lap normally causes an increase in muzzle bore diameter, requiring you to cut off a minimum of 1" to remove that enlargement.
Also what has become more prevalent lately is the fact that different bullet require different bores dimensions for best accuracy.
for example, it has always been known that Hornady bullets are a little fatter and if nothing else shoots, they tend to shoot in loose bores. top 1k shooter recently built a couple new guns with Broughton barrels (bore .30795) and the new 208 AMAXs would not shoot in them at all. After measuring the bullets and talking with Tim North at Broughton, they discovered that they were just too tight in a Broughton. Rebarreled the guns with Hart barrels (true .308) and now shooting like a house a fire. Not bad barrels but bad bullet/barrel mix.