I started with the Arbalete, (40" barrel), in 1951. Along the line I changed the barrel and put a line release on the bottom of the pistol grip, giving me approximately eight feet of line with a shock cord. The muzzle was a Johnny Carroll invention. I used one rubber. 5/8" surgical with a 1/8" hole, the length was 22". My Charlie Sturgill wishbones were made out of spring steel with extra large lead rubber holders. The wishbones were two inches long.
I tied my own rubbers using a waxed nylon line. I would, after tying, take a match and heat the waxed tie until it melted into one solid mass. I never had a wishbone or a tie come undone, (thanks Charlie). I tested each rubber to 122 + - pounds, that was my tolerance. I always put an extra rubber around my neck.
The Johnny Carroll muzzle was perfect for my one rubber but in testing I found that one side of a cocked rubber would vary 1 pound to 2.5 pounds. I figured this differential from one side to the other might throw my shot off, so I got some DC4 silicone grease and heavily greased the muzzle and rubber bend, causing the problem to go away.
Charlie made my competition shafts (still have them) with one notch and extending six inches beyond the muzzle. I taped the shaft so that in reloading the slider would fit in the muzzle tight enough as not to rattle, (no noise). When Charlie cut the notch in my shafts, it was 2 ¼ inches from the pistol grip. That gave me my 122-pound, one rubber gun that I used all over the world.
Figure it out:
Arm length 3ft. approx.
Gun 3.3 ft.
18.3ft. - Kill shot.
With the shock cord the shaft would hit the end with a "BANG". I always used the forty-inch gun, for holes, caves, whatever; I still have my three 40" competition guns with their Charlie Sturgil shafts, wishbones and Johnny Carroll muzzles. They have been silent for 40 yeas. (Arbalete)