An interesting thing which has helped my accuracy a bit in close range is to keep in mind the offset. Let me explain-

When you sling at a target you try to path a trajectory between you and your target and throw along that trajectory. The issue here is that the projectile does not actually fly from your eye but instead about a meter or two off to your right (or left for left handed). This is a very strong effect in close range and weakens as range extends. I've personally found that visualising the trajectory from the stone release point towards the target useful in hitting both close and medium range targets.
Now, most will do this kind of thing automatically, or simply subconsciously 'learn' the offset for their chosen range. I think that deliberately visualising it works better for me as it levels out the inconsistency over ranges and you won't do the wrong correction when switching ranges.

Anyone do anything similar?

I like both ways, subconscious/intuitive and deliberate visualization and correction of offset if I miss a lot.

I haven't, but now I'm going to give it a try.  I've definitely noticed that after slinging at fairly close targets (10-20 m is my usual in the yard), if I switch to distance slinging for the last few throws, my throws are usually off to the left.  Taking the angle of the throw into account, that makes perfect sense if my release point is staying the same.

Today I made a very similar discovery. I was down by the river, hurling stones at both short and longer range targets, and I found that I had a much greater degree of accuracy at about ~70m, than a close up ~20m. However, when I made a mental note of where the stone was being released from (in relation to my eyes), my accuracy at close range improved quite a lot.
I think that this could prove to be rather valuable, as with practice this 'awareness' of the stone will become instinctive.

As an afterthought, it seems a bit of an obvious thing to do...

Several observations:
I like to throw tennis balls because it’s easy to see where they hit, and I try to have 5 or 6 on hand so I can walk my shots in and make immediate corrections from shot to shot.

Another thing that helped me specifically with balearic style is to point at the target during the release instead of continuing to follow through and swing the hand past the target (the ball follows the hand off to the side).

Third, I take a cue from long-distance shooters and focus on consistency before accuracy. Rather than immediately correcting for offset, see if you can get multiple shots to have the same offset as the first, then make a correction after you are more confident that the problem is the lateral offset and not something else like timing.

JudoP wrote on Mar 5^th, 2020 at 2:23pm:

An interesting thing which has helped my accuracy a bit in close range is to keep in mind the offset. Let me explain- When you sling at a target you try to path a trajectory between you and your target and throw along that trajectory. The issue here is that the projectile does not actually fly from your eye but instead about a meter or two off to your right (or left for left handed). This is a very strong effect in close range and weakens as range extends. I've personally found that visualising the trajectory from the stone release point towards the target useful in hitting both close and medium range targets. Now, most will do this kind of thing automatically, or simply subconsciously 'learn' the offset for their chosen range. I think that deliberately visualising it works better for me as it levels out the inconsistency over ranges and you won't do the wrong correction when switching ranges. Anyone do anything similar?

Absolutely.  Also you can apply this to almost any activity that uses hand/eye coordination. Pool, basketball, bowling, etc..

Yes, especially with sidearm/Balearic style.
I think a large part of accuracy is being aware and present in the moment like this. I suppose you could say being scatter brained will give you scattered shots!

Extremely helpful advice. It really helped me closing in on small, ground level targets.
When doing a greek overhand I imagine it flying from above my head. I guess you can also visualize whether you throw a downwards line or a little parable.

I like Mr Noone's point about consistency, which I struggle to achieve

One thing that has helped me, which wasn't apparent to me my first few years of slinging, was to develop how a shot feels, develop the tactile feedback for how to correct it. When one is throwing by hand, it is easy to feel how the projectile left your hand, so you can easily make adjustments. You have to understand what it feels like when the shot goes high, when it goes low or when it is to the right or left. Since your hand is only in indirect contact with the projectile I, personally, have had a harder time developing this sense. And if I don't sling for a long time, I tend to lose it.

But if you can develop it, and if you can feel where a shot is going to go before it gets there, it is much easier to make adjustments. For me, sometimes a shot feels really good, but it still misses. So that tells me I still don't have a full understanding of how all the mechanics should feel.

I remember for a while, I would look at my target, close my eyes, sling, try to visualize where it was going to hit and then look to see if I was right (sometimes the stone was too fast or I was too slow to see where it hit). This was a pretty useful exercise for me, but not something I do on a regular basis. Maybe I should try again.

I think if you can visualize in your head how a shot is going to feel before you throw it, it is a useful exercise.

IronGoober wrote on Apr 23^rd, 2020 at 12:16am:

One thing that has helped me, which wasn't apparent to me my first few years of slinging, was to develop how a shot feels, develop the tactile feedback for how to correct it. When one is throwing by hand, it is easy to feel how the projectile left your hand, so you can easily make adjustments. You have to understand what it feels like when the shot goes high, when it goes low or when it is to the right or left. Since your hand is only in indirect contact with the projectile I, personally, have had a harder time developing this sense. And if I don't sling for a long time, I tend to lose it. But if you can develop it, and if you can feel where a shot is going to go before it gets there, it is much easier to make adjustments. For me, sometimes a shot feels really good, but it still misses. So that tells me I still don't have a full understanding of how all the mechanics should feel. I remember for a while, I would look at my target, close my eyes, sling, try to visualize where it was going to hit and then look to see if I was right (sometimes the stone was too fast or I was too slow to see where it hit). This was a pretty useful exercise for me, but not something I do on a regular basis. Maybe I should try again. I think if you can visualize in your head how a shot is going to feel before you throw it, it is a useful exercise.

Interesting, I will give it a try.

In the same vein I found at some point I knew how a good throw felt before I could ever actually articulate what was happening. A good throw had greater tension and more resistance at the beginning of the power stroke. It took me awhile to realize how important the lag angle of the sling is as you are initially pulling into the power stroke. Once I figured that out I began to focus not on the end of the throw but the beginning of the power stroke. It made a big difference for my accuracy.

I think the flight characteristics of a projectile is less important for short range accuracy than for long casts, as long as your particular casting tech is consistent, however bad it may be.  so as you attempt longer and longer shots the ammo needs to be increasing consistent.  to use archery as an example;
In my back yard l have many targets (2 ltr soda bottles) scattered about a hill side that give me ranges from ~2to 30 meters.  to avoid irritating or endangering the neighbors and/or damaging arrows I use low power bows and really old crappy, arrows w big feathers for targets out to 20 yards. it doesn't seem to matter much which combination of bow/arrow I use to have about a 3” group, which is good enough to hit my targets, while allowing me maintain  exercise, etc....When I use  the same eclectic equip at my local archery range, to the disgust of the good shooters, my groups expand to about 10” at 25 yards, and cant hit a 4x8 backstop w any 2 shots at 50.

My best slinging accuracy occurred years ago when I lived near 100 acres of abandoned orange groves waiting for a developers bulldozer as a kid in orange county calif, and used oranges as ammo.  They seemed to be a perfect size/weight ratio , and there was an unlimited supply of whatever size needed to match sling length. 

I bet oranges make a very satisfying splat!