It eases the transition from leed/throat to rifling. This is usually the point of peak pressure and where the bullet gets aligned/re-aligned or not. I believe the current thinking is 1.5 degrees but let PacNor advise you on this. No rhyme or reason to it but an 11 degree muzzle crown is the current favorite, 30 degree case shoulder, and 1.5 taper to the rifling. I'm not smart enough to tell you why.
"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli
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