Neck expansion diameter?

[MIEagle]

I'm preparing Winchester cases to shoot the .311299 NOE plain base cast bullet in my '03-A3 and '03 Springfields. The bullets are sized to 0.311. Using my RCBS FL sizing die plug, measuring 0.307, makes the inside neck diameter 0.305. Should I buy an RCBS neck expansion bushing to open that up and if so, how much? Thanks.

[JWFilips]

A thousandth under your boolit size

[Doc Highwall]

When you slug your bore whatever size it happens to be you should size your bullet .001" to .002" larger, and your expander should be only .001" to .002" smaller than your sized bullet.

What alloy and how fast you want to drive them makes a difference.

If your expander is more than .002" smaller then your bullet size you could possibly be sizing the bullet down during the seating operation.

More then .002" neck tension causes greater effort to seat the bullet which causes a greater bullet run out and larger groups.

[Outpost75]

0.001 under for soft bullets less than 12 BHN, to prevent damage to bullet bases.

If using harder alloy and heavier loads, such as over 2000 fps in .30-'06 to cycle a Garand, 0.002" under is better, same as for jacketed bullets, just increasing expander plug diameter as needed for larger diameter cast bullet. I use the RCBS .309" for loading .311" bullets in my Garand.

[GabbyM]

If you actually are getting .002" spring back after expanding. You need to anneal your brass, IMHO. Some shooters like it hard though. .001" is a normal spring back. Sinclair has the RCBS expanders as a separate item. .310".
749-014-393WS
Neck Expander Plug .310 749014393Neck Expander Plug .310
Mfr Part: 39869

[MIEagle]

0.310 Neck Expander Plug on order. I will also anneal all of my brass. Thanks!