Heat and/or humidity, Roy.
After straightening I temper each shaft(hardwood shoots and cane) and this is when I add the scorched coloration. This seems to help some but sometimes you just have to straighten a wood shaft.
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I did have something happen to me for the first time this summer. I built that real big arrow rack I posted and moved almost all of my arrows into my shop. It's made out of Galvanised steel and no AC. It gets over a 100dgs in there in the Summer when I don't have the fan running and I was suprised to see that a bunch of my Tonkin and hill cane arrows were crooked as could be.
Now I've got to straighten and then put a finish back on after using heat."
Looks like Eddie didn't get the memo again Pat!
Reckon we can now add Roy to that list!
Roy, it's really important to seal shoot shafts much better than dowelled shafts because of all the corrections that were made with heat. But before that, it's more important to reduce MC first, store upright in a controlled environment (in the house) for a period of time to periodically check for straightness. Once that criteria is met, moderate heat and humidity isn't a big issue, for a period of time at least.
Correct if I'm wrong, but it sounds like you stored your shoot shafts in an uncontrolled environment, made up the arrows, using heat of course, finished them up, and shipped. If that's the case, no way would I expect them to make it to your recipient as they were shipped............Art