Quote: 17-223 is longer by a large amount than 17 Mach IV or 17 Fireball.
I now realize that
the guy that gave me the brass called it 17-223 in reality it is 17mach !V, formed from 221 fireball brass
holding the two side by side i can see that the shoulder angle is a bit different . the 17fb being a little longer and steeper in the shoulder and a little longer in the neck.
I will load five or so and let'em rip and let you know how it goes