when to use the Lee .001 undersize sizing decapping

[edadmartin]

My Lee turret was purchased used and came with 2 45 acp sizing dies. a Lee .001 undersized sizing decapping die, as well as the standard sizing die
When would I want to use one die over the other??

[Ben]

Wow.......I just learned something new.
I never knew that Lee sold a set like that.

Ben

[44Vaquero]

Steel dies or carbide? The undersize would be used for jacketed I assume. Maybe the previous owner had a competition pistol with a tight chamber? It's not a stock item that's for sure.

[rockshooter]

I have several of the Lee "u" dies (9mm, .40/10, .38/.357). I have run into thin brass in the past and its nice to be able to ensure that the bullet is firmly gripped by the case. I prefer to use these just with jacketed bullets- which normally are smaller than boolets- so as not to risk swaging the cast ones. I don't think they are a catalogued item so I just call Lee customer service when I want something.
Loren

[edadmartin]

Ok I wondered if the undersize die was for either .451 boolits or for glock shot casings, that had a slight
Bulge.

[mdi]

Hmmm. Maybe to begin with it would be a good idea to start with standard dies and put that .001" die away. If you run into case sizing problems, then consider a special die. You know, K.I.S.S. until you get a handle on this reloading thing...