Looks good I have a Indian wild Mockorange walking stick sling I’ve been wanting to do this winter.
your the first to do a whole long stick that I’ve seen “here” in a long while , I like the feel of long handles

 

Thanks Clint. You've been doing some cool builds to, interested to see your mock orange build. Maybe the long handle adds a counter balance?

 

You could also make it where you wrap string from fork to fork and make your knock on your dart like a arrow knock

 

I just tried that and it worked really well, I think it might work just fine with a normal sling pocket and bands. The arrow spear could fit into the hole in the pocket if it's not to heavy.. Starting to slim everything down.

 

proof of concept works. Flings a 5 1/2 foot willow 'spear' pretty hard, the elastic of the bands is a nice springy action... The rock sling throws egg sized rocks hard, just need practice. The slingshot is surprisingly consistent, I think the long handle really has an affect. Now I just need to sand make a better pouch, add some carvings, maybe a little wood burning, and lots of practice.
Oh and a .22 rifle and shotgun barrel would be nice to add on too.