Well unless you can post a video we have to take it a step at a time with the most likely culprit being the first to debug.
Looking forward to hearing from you tomorrow.
BTW - a good recipe for a temporary leader is to use the 60/20/20% rule.
A leader has at least three parts, the butt, the taper and tippet
These are often broken down into smaller segments again but for the purpose of the test just divide the leader (say 8ft) into 60% length (58 inches) depending on the fly line in this case a 7wt well just use 20-25# test, then a taper segment of 20% length (20") of say 12# then 20" of say 8#
You can see this would not make a good fishing leader, but for the purposes at hand go for it. Later on just split the three into pieces to step down more so a 30# butt could taper to a 4# tippet by stepping more as you go etc.
Keep in mind the more it tapers the more reduction in energy is achieved and the less kick you should experience unless the taper is too radical. The trick is to make it smooth turning over.
Then you might have other influences from the rod path, etc but even the best casters will get a whip-over without a leader.
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