jaybe
That sounds just about right and common
This is from MMP:
The big difference between Black HPH12 and HPH24 is HPH24 is .002" smaller
in loaded diameter. Loaded diameter is a sabot with a bullet inserted.
With a .452 diameter bullet the HPH12 is .507-.508" diameter, the HPH24 is .505"-.506" diameter
The crush rib is .503 -.505, have you tried them yet?