.356 in 9mm

[pacrat]

False.

Carbide dies size size the 9mm using a tapered carbide insert. This insert is dramatically different from a carbide insert for a straight walled case. A 9mm carbide insert induces a tapered profile in a fired 9mm case. The body is larger in diameter at the case head and smaller at the case mouth. The degree of taper varies between die manufacturers.

If you ran a 9mm case through a .380 die you would end up with what you describe, but that is not the case with 9mm dies.

Bingo again.

9mm case has .011" taper over .754" lenght

380 case has .001" taper over .680" lenght

With base dia differences of .374'-380 and .394"-9mm. A 9mm case in a 380 die would have severe and extreme wasping after seating bullet.

The fact that they both use .355/6 dia bullets is the difference in brass thickness required to contain the much higher pressure of the 9mm

It's all about geometry.

[ar15barrels]

False.

Carbide dies size size the 9mm using a tapered carbide insert. This insert is dramatically different from a carbide insert for a straight walled case. A 9mm carbide insert induces a tapered profile in a fired 9mm case. The body is larger in diameter at the case head and smaller at the case mouth. The degree of taper varies between die manufacturers.

If you ran a 9mm case through a .380 die you would end up with what you describe, but that is not the case with 9mm dies.

Different makes of dies are made differently.
Many are not like you are saying.

[J-cat]

Lee, Redding, RCBS are. What do you call many?