.223 frangibles SoftShot safety load

The headstamp is “R.P 223 Rem”. I got it because of an unusual projectile shape, I guess this shape makes it fall apart faster. What is “42ET”?

Custom Cartridge Inc. currently in Columbus, MT originally located in Goleta, CA

Bullet is 42gr, International Cartridge Corp. Frangible, (wide tip). Have no idea as too meaning of (42ET) other than weight.

Custom Cartridge also produced a SoftShot HP by drilling out the above 42gr. but not sure of wt. I have examples of both from the Goleta, CA location