sizing? Why?

16 March 2003, 02:42

cmcalpin2002

sizing? Why?

I think I did read why somewhere but now I cannot find it. If a mold is .358" then why do the bullets get bigger(.359") afterwards to require sizing? Cory

16 March 2003, 02:57

aladin

quote:
Originally posted by cmcalpin2002:
I think I did read why somewhere but now I cannot find it. If a mold is .358" then why do the bullets get bigger(.359") afterwards to require sizing? Cory

Your saying why does a 358 throw 359 slugs?

Usually the mold dia designates the groove dia the design is suited for. And alloys drop at different dia's-- in a 358 from pure lead to linotype might produce a 2 thou variance. And for instance many old Ideal molds labeled 308*** throw slugs 311.

IMO-- shooten UNsized IF they chamber safely. Then work you way down in dia if desired to tune the loading to that particular barrel.

16 March 2003, 04:15

Leftoverdj

As Aladin said, different alloys produce different size bullets. And there are manufacturing tolerances to consider. Since slightly oversized bullets are much less of a problem than undersized bullets, moulds tend to be made a hair bigger than the listed diameter.

This works to our advantage since sizing and changing alloys lets us change bullet diameters. One mould can be used for both 9mm and .38. Another mould can be used for old .45 Colts which need a bullet about .454 and newer stuff which has the .45 ACP bore size of .451. Aladin mentioned the moulds intended for .308 bores which drop bullets big enough to work in stuff like .303 Brit and 7.7 Arisaka.