Why are cast bullets .001" larger?

[G37]

This is a questions I've often wondered about... Why are cast bullets almost always .001" larger in diamter?

Example:
Jacketed bullets for .45ACP are always .451", but cast bullets are most often .452"

If I can find cast bullets that are .451" should I get those instead or .452" cast bullets? Cons/Pros?

Regards,
G37

 

[msg.drew]

Personally I shoot .452 cast bullets out of my 45's its a pretty commen size you can get a sizer to undersize them to .451 but its not nessary and they might not work as well as the larger ones.

Cast bullets are much softer then jacketed. Even the strongest and hardest cast bullets are only 1/3 as strong as their jacketed cousins. To resist deformation and gas cutting (where the hot powder gases melt and/or deform the lead), a cast bullet must be larger then bore diameter. After determining bore diameter and adding .002”, the correct bullet sizing kit or sizing chamber can be selected