I'll add that following pointing, Al's bullets were EXTREMELY difficult to eject from the die, while "my" bullets ejected normally. Even
slathered heavily with excessive lube, Al's cored bullets put the K.O. pin spine, "to the test"! As stated, the heels appeared, "shaving sharp", thus, were trying to dig/cut into the die walls - RESISTING ejection!!
Via my memory and Mitutoyo (digital) & Starrett (vernier) micrometers (and we used both), Al's 'cored' diameter was 0.3078", while those from my core-seat die were/are 0.3081", or, 0.0003" difference in shank diameter. Following pointing, the shank Dia. of my bullets is in the 0.3083-0.30835" range: expanding up 0.0002, while Al's pointed [shank] Dias. ran 0.30845-0.30850": expanded-up about 0.0006", or three times greater outward expansion . . . it appears that this IS a place where 1/10,000Ths of an inch DO matter!
Skimming through the memory bank . . . AND some early "90''s" notes, it appears that we "jumped to the/a [correct] conclusion": the SHARP heel is likely the result of the more rapidly expanding jacket releasing the core, which slides slightly forward before the jacket 'catches up', thus, the malleable jacket accommodates forming the SHARP heel prior to re-mating with the core . . . in short, the EXPANDING-UP principal, put to the test!

A perusal of comments by George Ulrich (maker of GREAT dies), in the resurrected Stephen Perry thread, reveals George's questioning - relative to carbide dies - the expanding-up principal . . . damn, George may be correct AGAIN!

Not that expanding-up is bad, but as in all things, there's a limit: several of my smaller caliber carbide die sets, executed very competent makers (Niemi, Ulrich, Detsch), swage-up only 0.0001" and some, not at all! Upon receiving one set, of the latter type, the die maker informed me that fro that caliber, compared to tool steel, "carbide is too slippery to assure proper expanding-up" . . . and, though, at the time, I was not endeared, that die-set makes GREAT bullets.

RG