I've looked into the drilling of the hole option. You don't have to have fins on the spear to do it. It's a good way to transform a biller or jbl into a faster shooting more accurate gun. I had planned to do that to my biller but had some trouble trying to figure out how to keep the spear firmly in place at the tip of the muzzle without risking tangling the line up during the shot. I eventually just went with the low profile slide ring instead. Hopefully someone at biller will make an interchangeable muzzle that is completely open and you can rig up just like a riffe. I thought about modifying the current biller muzzle to do this but the risk of degrading the structural integrity of it by cutting away too much of the plastic prevented me from doing that. The thought of the muzzle snapping which I had a spear with 2 5/8" bands loaded put a damper on my do it yourself attitude. There are some interesting modifications for the billers on this post. The shaft has a fin for the string, but that is beside the point.
http://forums.deeperblue.net/america...caribbean.html