+1 on the plunk test but I've been using a taper crimp die since before the FCD came out, haven't seen the need to try it. With all the different cast bullet profiles any published OAL data is almost useless.
I'm guessing the only way to figure out why it didn't work is to try at least a few. May be able to figure it out by measuring them after casting, may have to shoot them.
I've begun a "casting notes" section in my loading record book, right after my "shooting notes" section for each cartridge. All I have to remember to do is write down my observations after shooting or casting.
It's aggravating to not remember if a certain load or component worked but sometimes trying it again works better.