casting under size

[loiner1965]

why does my rcbs .470 mold casts bullets of pure lead at .465 whilst all my lee molds cast more or less the same size as stated on box ?
this is using the same pan of lead and both dropped into water.
i know about bullet shrinkage so i tried air drying the freshly cast bullets but still no difference.
apart from the obvious why is this?
both molds produce lovely boolits but i do love the rcbs mold

[geargnasher]

Because the Lee moulds are made of aluminum, so the expansion ratio is different. And odds are you're needing to run the moulds much hotter than with "regular" boolit alloys for a good fill, so the aluminum expands more to cast the same size (about) that it would with a less-shrinking alloy with a lower melt point and lower typical casting temps for the mould itself. The steel mould can't make those kinds of dimensional excursions.

Gera

[loiner1965]

many thanks....thought it was that but wanted comfirmation from the more experienced casters to comfirm

[bobthenailer]

I dont know if its a rifle or pistol you are casting for ? but RCBS rifle & silhoutte moulds weights & size are established with linotype alloy , and pistol moulds are done with 1 part tin to 10 parts lead and round & mini balls are done in pure lead so if you are useing a alloy softer than used at RCBS then the bullet will weigh more and be a smaller dia.

[loiner1965]

hi bob.
loading for a mk4 martini and a mk2
it is pure lead i am using but i do have a supply of linotype i could mix in...but at the moment i am getting groups of around 3 inch at 110 yards and no leading issues

[gray wolf]

Water dropping pure lead does what ?
Rcbs molds will not ( most times ) give the listed size unless you boost up the antimony. ( as said ) They sure do make nice boolet though.

[243winxb]

Antimony is needed in an alloy for water dropping to harden the boolits. Antimony will also increase the bullet diameter as it drops from the mould, but not .005"
getting groups of around 3 inch at 110 yards and no leading issues Don't change a thing. :-)

[loiner1965]

That's why I sticking to how I cast the bullets lol
http://img404.imageshack.us/img404/5670/img0109ts.jpg