Quote:

The FM is rifled to allow the bullet to be perfectly aligned and engraved to match the transition into the barrel. 

After rifling the FM is removed and taper reamed to groove dia. at the muzzle end and to bore dia. at the barrel end (pinned end) then slightly belled to accept the typically larger bullet base band. There are other alignment issues to be addressed in the starter attachment also. 

End result - same bullet positioning as breach seating from the other end but fin-less.

Whilst I do realize that this might be a little off the subject but as fins to the base of the bullet was mentioned this might be relevant.
Years ago when I was into pistol and air rifle competitions I remember reading an article either by Anschutz or Walther who found that on testing for accuracy that any slight nicks or other to the base of the skirt of an air rifle pellet affected accuracy whereas it didn't matter if it occurred at the nose.
I also used to wonder if the not very smooth base of cast bullets for my pistols also had the same effect.
I don't cast bullets anymore but have experimented with jacketed bullets mainly when using R/F jackets to get the firing pin mark out.