Here what I go by except that I use three intermediate expander balls 6, 6.5 and 7 mm.
I have some brass that has been shot twice now and they are holding up better than reloaded 303 savage brass.
> The formula for 220 Swift to 303 Savage...let's see...
>
> Get virgin 220 Swift brass from
www.MidwayUSA (can get
> it online). There is a particular shell holder for it
> that no other cartridge uses (I forget which one,
> Midway has it). I ran the 220 through a medium neck
> resizer at first because if you go from .224 to .308,
> it screws up the neck and shoulder...you need an
> intermediate size. I use the neck expander from a 6.5
> Jap.
>
> Next, you Put the 220 with the 6.5 caliber neck
> through the 303 die. The shoulder will be shortened,
> as expected, and the neck will be way too long. I use
> a Forster case trimmer and wheedle the neck length
> down to the 303's length. Once you chamfer the case
> mouth...that's it. You are done. Pretty simple.
> I have loaded these with full power loads (Speer 180
> round nose over 30 grains of 4895) and get three inch
> five shot groups at 100 yards with tang peep sights.
> They don't stick, and you can't tell the difference
> between the 303 and the re-made 220's unless you look
> at the rim of the cartridge base (or the headstamp).
> The 220 rim is a little thinner, but I honestly
> haven't seen any headspace problems.
> I have a lot of original 303 brass, but the commercial
> supply is all gone. I thought I'd try the 220 thing,
> and am glad I did.
>
>
> Best of luck, be careful, and watch what you are
> doing...
>
> Good shooting.
>
> GD