Dies sizing vs seating

[robbor]

I started thinking about trying to use existing dies as forming dies, and others recommended using seating dies as my forming dies. Anyways i just received some 250 savage dies and i went ahead and grabbed my inside mics to measure the dies to see how much of a difference there really was. I measured at the neck then again inside but at the base of the die, my inside base measurements are not an accurate reading of the base of the dies but a good rough indication so compare size. So these were secondhand old rcbs 250 savage dies, nothing special.

Sizing die Neck .276 Base .460*

Seating die Neck .294 Base .472*

According to my manual the neck of the chamber should be .286
I was surprised to see more than .010 difference and what seemed like a huge amount of slop in the neck area of the seating die. So as others had stated a seating die would make a very good intermediate forming die.

 

[dmickey]

What caliber are you trying to form? From what parent case? I have Nonte's book on cartridge conversions as well as Donaldson's. I may be able to make some suggestions.

 

[robbor]

Im pretty set. I was thinking of being able to reform brass to try thick necked 22-250 in my factory rifle.
I already had 300 sav dies, i just got 250 sav dies for $12.
I just did not know the seater dies were that over sized and they can be used as a intermediate form die in certain situations. I think im going to try reforming some 243 and some 308 to see how they come out and how much the necks thicken up, and if they make any diff.
Im after necks that are 4-6thousandths thicker total but turned even.