Another good reference for arrow shaft tuning, scroll down to bare shaft testing.

https://www.fenderarchery.com/blogs/archery-info/basic-tuning

Excellent video! I really enjoyed it! Nice shot.

Check out this video, very helpful.

Do these boards have the right grain?

I had a Black Bear Hunter, and a Stag Hunter that had blonde maple risers, and didn't have string grooves or tip overlays

Definetly look different!? Still a recurve though. The shorter ones always seemed to have more "curve" due to the angle of the limbs coming off the riser.
 Like the difference between a K-Mag and a Grizzly.
I have a bunch of old Bear recurves and all of them seem to shoot best at about 8-1/2 inches

Here they are from the same '77 catalog. You can see the difference in limbs, and the BBM doesn't have grooves on the limb to keep the string centered either. K-mag at 49" and BBMag at 51". I wonder if brace height would still be about the same between the two?

I know that the black panther models were for big box stores, and that they were never in the catalogs. I wonder if it was just a newer design that got rapidly overshadowed by the up and coming compounds? It looks a lot like a shrew bow to me when strung.

Great write up. Congrats on the bear!

Well done.  Congrats.    

Neither of those shafts should be weak. I think your arrow is bouncing off the shelf, porposing and fishtailing, yielding a false weak. I'd start by checking the brace height.  If it's too low, it can cause either of those problems.  If it's where it shoud be, raise your nock point, as McDave suggests. Of course, it could also be a form issue.