Thread: Stretch marks using Lee dies on 45-70 solved (but not quite understood)

The short story is that I found that by taking more that 7 seconds (precisely) to slowly put the brass up into the die, the ugly stretch marks are avoided.
I also measured before and after and found that no extra stretching happens if you quickly pull it back out (it may effect concentricity but i doubt that effects a 45-70 at 50 to 100m tops)

The bit i'm interested in is why? Is it heat generated by normal resizing speed (say 3 seconds on the initial motion). I use enough resizing wax (not using enough produces a hazy finish on other cals).

If it is heat, what is happening to the brass to form long ripples like you can see on these loaded rounds? It looks ugly and no doubt causes some variation in capacity/MV/POI.

*As you can see on the resized and bell mouthed cases, taking it much slower does resolve it completely. Does this also happen on Hornady or RCBS dies?



P.s that long trailing mark is an ejecting scratch from my Bergara break barrel extractor claw. Cost of doing business.