[9x45]

In a pistol, no. And it's not really a crimp at all, but rather a de-bell step which is just enough to take the bell off from the powder thru die. The crimp does not hold the bullet in place, it's the interference fit between the bullet OD and the case ID. Over crimping can lead to bullet setback.

 

[9x45]

For semi auto cases, especially 9mm, it is TRUE. Putting a bullet in a fired (un-sized) case makes no sense. It is not the correct ID diameter to provide an interference fit. So try this, load some 9mm without a crimp and shoot them in a S&W revolver. It doesn't need to be de-belled (crimped) because it does not sit in a chamber. The less taper in a semi auto, the less sensitive the round is to de-bell, such as a 10mm or 40S&W at .002" per side versus a 9mm, at .0055" per side.

 

[9x45]

The above is correct, but that is not what you originally wrote.

This is GlockTalk, not RevolverTalk....