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?

Attachment 184186

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

A bit of a wild guess, but perhaps it's dimpling from a buildup of the sizing wax?
Maybe with the straight walled case the wax from the neck end builds up and causes dimples, but pushing the brass slowly into the die allows time for the wax to disperse more evenly?

I was thinking along similar lines...chuck die into icecream container with some 2stroke fuel...give guts a bit of clean out with cotton bud....or just spray insides with crc then try another LIGHTLY lubed case and see....the walls are thin...but not that thin....never had issues myself with .45/70 infact found it a doddle to load for.

I might try this. I did try that hideous 'oneshot'at some point but i cant recall if i sullied this particular die. Im really sparing with the wax eh. A slight wipe with a fingertip in the tin. Brass is amp annealed too.

I use tiny smear of vasoline on fingers,and twirl brass between fingers...can barely see it on brass.....never had issues with this once I learnt to keep off the neck of bottle necks....why I know about cleaning dies lol.

what projectiles are those??? seem very deep.

Could just be a slightly tight FLS die too if it still happens once fully cleaned out

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Originally Posted by Micky Duck

what projectiles are those??? seem very deep.

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These are just trademe cast bullets. I take the bergara barrel completely off and keep seating deeper till the whole round drops fully in without stopping on the lands. I suspect ive got a chamber cut for those short arsed 'leverevolution' rounds?