Homemade sizing die

[kakan]

Hello, I'd like to make my own sizing die for a cartridge with straight case (without any taper, exactly like .45 ACP, .380 ACP, 9x18 Mak etc.). I realize brass is springy, so the sizing diameter of my die must be *a bit* smaller than the OD of the case I want to get after sizing.
Can anyone help me, and tell how figure out what this inner diameter should be?
Thank you in advance.

[elk hunter]

KaKan,

Welcome to the forum.

If you already have them, you can try measuring the three dies you listed and a before and after sizing measurement on cases should give you an idea of the spring back, but it will vary depending on case hardness and thickness.

[largom]

kakan, welcome aboard! Make a chamber cast of the gun involved, cut your die about 2 thousands under the cast Dia. If this is too tight you can always open it up a little.

Larry