I finally finished my bird bolos (I can't even remember when I started them. They'be been floating around in the bottom of my braiding bag for a long time)
They are made from a small steel ring in the center. The lines are each made from 8 strands of mason line split into 2 groups of 4 (each line is a 4-strand braid).
The weights are made from wire rings "moused" with mason line connect the weights to the lines. The weights themselves are .68 caliber lead rifle balls, covered with monkey fist knots made from flat paracord.
I finished the lines just above the weights by wrapping them with flat waxed nylon thread I use instead of artificial sinew. Then I toasted them with a lighter to melt the wax together.
I haven't thrown them yet. First, all the birds gone south. There's too much snow. Second, it's usually been around 0 here. Too darn cold. I can honestly say after tying 6 successful monkey fist knots and I have no idea how many failures, I can thoroughly detest having to tie it. Maybe it's easier if there is no weight inside, or if you are making a larger knot, but it was kind of a royal pain in the...place where politicians keep their heads.