Ok so here is the start of V2 with my analysis of Matthias design that CA pointed me too. It's a different approach from my V1 incorporated weight.

On my bullwhips I use a steel BB core that is not practical for slings. On a sling I realized you don't need to braid the lead weight fishing line into a core. Just make your finger loop. Then cut multiple strands of the lead line. Measure your length to your pouch. Partition and split the individual lines. Mark all points and tape together (I use hockey tape). And voila you have a complete core. The rest will be plaiting said core to the desired thickness and design. 30% faster to make and just as strong.

Don't have time this week but will begin plaiting the core next week and update you guys then.

Yeah! Seconded! I'm excited to see how this turns out.