Ok, so I have had some experiments done recently, and have found something interesting regarding energy, momentum and police bean bag bullets. Bean bag rounds for police travel an average of 265 fps, and weigh 610 grains roughly, that gives us an energy of 95 ft lbs, and a momentum of 3.2 kg×m/s. The bean bags dimensions are 1.5 inch diameter and 5.5 inch length. This tells us that they are clearly designed to only deliver the energy in as less lethal a way as possible in the form of a soft sock essentially, filled with dense lead beads. With a 2.5 foot sling, using a 2044 grain lead ball hand made to be 1.1 inch wide and long, I have recorded speeds of 140 fps (which is easily beatable with a longer sling, but the idea is compactness). This gives us an energy of 88.9 ft lbs, and a momentum of 5.6 kg×m/s. That is vastly more compact and around 75% more momentum. Knowing this, we can have a reference point on what these energies can roughly do to soft tissue by looking at bean bag round injuries, then look at how much more effective a lead ball like this would be, even with it flying slowly out of a short sling. I think we could even make a mimic bean bag round for slings, like taking that lead balls weight and make it into small pieces and put a sock around it and it would have the same energy, but vastly more momentum!

This is mostly just me rambling, but any information that may be used to compare damage output of the sling to something well known (like the bean bag rounds) in order to put an end to the idea that the sling is a toy like the general public think, is useful.

Yep, basically a sling is a tool.
How you use it, is what counts

For the record, I'm extremely happy for slings to be regarded as 'toys' by the authorities
It makes it far less likely that they'll be made illegal and means that you can carry one anywhere and post them around the world with impunity