I've been playing around with pinch grips recently. This is a grip that seems to be fairly prevalent amongst primitive archers. It's used a lot down here in New Guineau. Conventionally it wouldn't be thought to be much cop for
ELB, because of the relatively higher draw weights. However it has a couple of advantages. For me it avoids much strain on the fingers, because there's no hook. So if you've got tendon issues, arthritic fingers, etc it's a bonus. the other thing is that it reduces paradox because there's not a lot of sideways pressure. The biggest con seems to be the limited draw weight. But yesterday I saw an idea on Paleoplanet that gets round that. You make up a half inch wooden bead and put it on a D-loop string around the nock points. Then you set the arrow and draw by gripping the bead. It's brilliant. The user was saying he has no probs drawing 70 lbs. I made one up and was playing with 30 lbs today. I'm going to show it to a couple of old mates who cannot shoot fingers anymore. Hopefully it might get them going. If anyone's interested I'll attempt to post some pics.
Blakey, I recently did some tests on different bow strings. In particular looking at string weight. What I discovered was that adding weight to the center of the string is about the worst thing you can do. It affects the bow's efficiency (i.e. how much potential energy is transferred to the kinetic energy of the arrow). It is diffcult to give you an idea of how much because it depends on your bow, the weight of your arrow. I would however say that a 9" serving uses 8' of thread and can weigh up to 12 grains in weight. Two brass crimp nocks weigh approx. 10grains. For my bows and my arrows, these two factors accounted (if memory serves -excuse the pun - me correctly) for approx 2-3% reduction in bow efficiency. So assuming you bow, with your arrow shoots at 150fps, 22grains of additional weight in the middle of the string will reduce your arrow speed by between 3 and 4.5fps. The effect seems to be worse for lighter arrows than for heavier ones.
Depending on the length of the D loop, the amount you bend the bow will reduce so you will store less potential energy too.
To overcome the reduction in potential energy stored and efficiency you probably need to shoot a higher poundage bow.
You might want to consider losing the D loop and thread the bead directly on to the bow string. When choosing the bead, use the lightest material you can find. Another suggestion is to compensate for the bead by making the bow string from a different material. I know a lot of traditional archers stick to B55 rather than use one of the fast flight based materials. Since adding weight slows the bow down, you can probably get away with speedening it up again using a modern material. Depends on how risk adverse you are as it is your bow.
Part of my string expereiments included crimping bits of lead to my bow string. They hurt like hell when they came off the string so be carefull with using a wooden bead. It might split and then you will have created a stone-throwing bow.
Have fun tinkering.
P.S. If you manage to get access to a chronograph, I would love to know what the drop in arrow speed is. Otherwise, let me know what you come up with and I can test on one of my bows and measure the difference for you.