Since I'm an old friend of Byron's and actually had an encounter with Bob Markworth in the late 70s (More about that later George:^))I think I can lend some insight to the question and comments. I've heard Byron say that he uses hunting weights for exhibitions because that's what he's accustomed to. No tricks or strategies involved at all. He shoots what he knows.
Now George, about Bob Markworth. In the winter of 1978 I was doing my student teaching near Ft. Knox at an area middle school. Back then SE US school's offered monthly entertainment programs to their students;I believe they were called "Southern School Assemblies". Bob was performing at my school and, as he often did, enlisted audience members to participate in shooting a bow so he could have them see how easy it was to get started. My supervising teacher knew that I had shot AAU and NAA at my university, so began jumping and pointing to me when Bob began collecting his "volunteers". He took the first "shooter" and had them stand about 10 feet in front of an Olympic style indian grass target mat so they could at least hit the target face. Bob would then have them back up a few yards until they missed, which usually occurred within the first 10 or so yards. Of course the target was BIG, an Olympic size target mat! When it became my turn:^); I hit the gold at 5 paces, then 10 paces, 20 paces, etc., until I had finally reached the back of the dang gym and a WALL - well over 100 feet! The kids in the upper bleachers were going absolutely crazy! Even at the end of the gym I was still using the lightweight target bow to drop arrows into the gold. Bob was HAD! You should have seen the look on his pretty assistant's face! By moving me back in small increments Bob was actually helping me with each arrow, as I was able to make small adjustments between shots! I had been trained in "point of aim" AND gap shooting so I was basically walking the arrow into the NAA/FITA gold. Man, does seeing Bob's name bring back some memories! That man did a lot of good promoting archery and it's history to all age groips; I remember seeing him once or twice on the Tonight Show and other national programs.