I've been slinging regularly (once or twice a day) the last two months, with two slings: 1. longish braided jute, small pouch, as long as middle finger to the breastbone (folded); 2. shortish folded nylon line, rather shorter than middle finder to the shoulder (folded). The target is a sofa-sized grafitto (about 2m across by 1.2m high) at ca. 23m distance. Shooting style is 1-3 overhead rotations followed by sidehand-ish release.

My most accurate and pleasant shooting is with the short sling and biggish (1.5-2 eggs in size), heavier stones (sometimes 4-6 out of ten shots on target); the longer sling shooting smaller, lighter stones (golf ball size) has become unpleasant and unmanageable at this range, lots of careless shots pulling left (i.e. late release) and even fouling. However I seem to have gotten better with the long sling shooting at longer distance (estimated 40-50 paces), sometime hitting the bushes or trees or rocky outcrops I aim for (to my surprise). The short sling also gives OK results at middle distances in terms of reach and accuracy, though.

[Edited for typos]

Yes, I think when I shoot I bit further I concentrate on the target, the bad shots at close range with the long sling often happen when I'm trying to concentrate on the shot (the body, the sling opening)-- which in fact only makes the bad shots more frustrating. But the greater power of the sling also makes it harder to control at the shorter range. Which is no doubt why Jaegoor uses a shorter sling for his target work.