Shale wrote on Apr 25
th, 2019 at 9:21pm:
It's interesting that the Bayeux Tapestry depicts a sling being used to hunt or drive birds away from a field
https://www.google.ca/search?q=bayeux+tapestry+sling&source=lnms&tbm=isch&sa=X&v...but does not depict the sling being used in battle. It seems that the sling was sufficiently common for hunting/farming to warrant inclusion in the tapestry but not sufficiently significant for fighting to be included in the battle scenes. The fact that it's included at all might mean that a fair number of people were somewhat skilled with the sling in the medieval period. But even if that's true, by the 11th century soldiers were just too well protected for it to be an effective weapon in most circumstances.
I would be careful with using the Bayeux tapestry as a source itself, as there is a good chance that there will be biases involved. It would be a bad showing if the Normans were shown up by slingers, much like it would be a disappointment to show Taillefer, a musician, who likely made the first kill at Hastings and is said to have sang the Chanson de Roland to the English troops and juggled lances from horseback, whereupon he threw one at the first Anglo-Saxon to present himself. In all, the guy had style!
You don't want to be the Norman knight getting shown up by a minstrel.
That said, there are more period sources and evidence to suggest that Slings were primarily being used in sieges and less in battles. I do not think that the 'effectiveness' of arms or armour should be the main consideration, given that Pre-1100's/1200's, The best armour of the period in Europe tended to consist of maile itself worn over a woolen tunic, or maile worn over a aketon. Good maile itself can provide a stunning level of defensive protection, but the sheer momentum of such an impact by a slingstone is likely going to bypass the metal and the tunic to the point that bone-fractures are a likely conclusion to a direct impact, even at somewhat extended distances. Even an aketon likely wouldn't afford much protection, given that Aketons tend to be thin themselves and were probably largely textile in origin with little batting.
If you are considering over-armour defensive garments such as a Gambeson, then this is when things would differ. This however, tended to be a later invention. You would probably be looking at the mid 1100's before such things became known, and into the 1200's before documents such as the Kings Mirror suggest that this was a 'recommendation'.
You can see what this would have likely looked like in this video.
https://www.youtube.com/watch?v=n8j1wT81KlIWith a Gambeson + Maile + Aketon configuration likely becoming common in this period (1200's) among knights and men-at-arms, slingstones are presented with a challenge. The firm Gambeson would absorb a lot of the impact and would likely take the brunt, whilst the maile and aketon would probably absorb the rest. The likelihood is that a slingstone would probably be rendered ineffective against this combination, but an impact against the arms or legs would probably still result in an unwanted 'conclusion' to a fighting season.
Into the 1300's, with the arrival of Coat-of-plates and transitional plate armours, You would really be looking into Staff-slings. Slings could still be effective however, even into the 1500's. The Spanish feared them, even in a period in which they had easy access to munitions-grade plate armour. To me, armour developments were probably not the primary motivator which phased the sling out of battles.
One should note, however, that above-mentioned plate armours were not worn in conjunction with an over-armour soft defensive textile, and as a result, the plate armour would likely be heavily dented by sling impacts. This could have a considerable impact on the outright defensive capabilities of the defensive armour in question, given that plate armour often depends on precise shaping to cause most arrows and bolts to glance off, and a dent would be a point in which the armour becomes weakest and would promote a surface by which arrows or crossbow bolts are more likely to find 'purchase' in a given armour and thus a higher risk of penetration. Before the middle of the 1400's, plate armour was often paired with over-armour padded garments such as the Jupon, and as such would probably be more resistant to slings.
Slings were used at the Battle of Falkirk and at the Battle of Najera, so they certainly were used even when they were presented with 'difficult' armours that could resist the power of slingstones with a high probability.
Other issues are probably the most likely reason for slings to be 'fazed' outside of battles, outside of armour development. What these issues are, however, is the biggest problem...
More likely reasons probably include limited access to populations with good slingers, difficulties of training, the general trend for equipping Urban armies consisting of Urban burghers and freemen etcetera (City folk don't often do a lot of slinging). Slingers sometimes take up more space than archers and generally need to be used/utilized in a different way to archers, which might be some reason why they might be fazed out of battles. Skirmishers in general were also gradually fazed out of medieval battlefields as well.