Sean Bean states the following in regards to the light cavalry sabre: "The injuries it caused were so horrific that the French had previously tried to ban it from the battlefield." It can be found at 14:32 of the documentary on the link provided (The link itself should bring you to that exact moment.) Prior to the Napoleonic Wars, was there another example of weapons being banned? Was this something that was common practice between warring European nations?
https://youtu.be/SScubWbQKhI?t=868
Edit: Just to clear any confusion, if there is any, I am not referring to "Sharpe's Waterloo." :)
Edit 2: (Originally I wrote this in the comment section but I think it provides better context and gives a chance at a more elaborate answer someone may be able to provide. It also let's me progress the question to a more precise one in regards to the origin of these claims, where they started, and how it cannot be confirmed.)
I just read through a section of the novel "Tools of War: History of Weapons in Modern Times" by Syed Ramsey on the British Pattern 1796 Light Cavalry Sabre that reads:
Its blade, unlike other European sabres of the period, widened near the point. This affected balance, but made slashes far more brutal; its action in the cut has been compared to a modern bacon slicer. It is said that this vicious design prompted unofficial complaints from French officers, but this is unconfirmed.
I'd imagine the documentary was just going for the shock value through exaggeration, which admittingly is frustrating for me.
Ramsey, Syed. Tools of War: History of Weapons in Early Modern Times. Alpha Editions, 2016.
By light cavalry sabre, I'm assuming you are referring to the Pattern 1796. Now while there are numerous accounts about its efficiency, there are no accounts of the weapon being banned or even a formal protest by the French to the British regarding the weapon.
From “Sword, Lance and Bayonet”, Charles ffoulkes and E.C. Hopkinson
As a cutting weapon (M1796) in the hands of a skilled swordsman its effect must have been terrific, indeed there is a legend that Napoleon’s generals protested in the Peninsular War against the ‘unsportsmanlike” behavior of Wellington’s Light Horse. As Napoleon’s Light cavalry were using the same sword we can but assume, if there is any truth in the legend, that the complaint was rather of the greater skill and more expert swordsmanship of the British cavalryman.^(1) As a thrusting weapon it would be well nigh impossible even for an expert fencer to achieve a satisfactory result.
The footnote leads us to Graham, "History of the 16th Light Dragoons", I, 245
The cuts...inflicted by the British cavalry with this weapon were terrific, and their severity was actually on one or two occasions formally complained of by French generals. They thought their wounded savagely and unnecessarily slashed.
That's it. There's no earlier reference or quote from a named individual, either French or British, supporting a ban. The lack of supporting sources suggests that it simply became a myth as something said by an enemy fearful of the mighty British weapon.
Moving on to the next part of the question, and remaining confined to the Napoleonic Wars, and earlier (which disqualifies the M1897 Trench shotgun), the weapons commonly subjected to regulations have been chemical and biological weapons. There have been psychological and moral objections to the use of poisonous substances against humans. These sentiments, first expressed in customs on the conduct of war, later became codified in the laws of war, humanitarian law and the law of disarmament.
The earliest recorded prohibition on the use of poison is contained in the Manu Smriti (the Tradition of Manu), compiled in the second or first century BC, which forms one of the foundations of the Hindu code. This exhorted a king not to use poisoned weapons.^(1)
During the early middle Ages, the Christian Church experienced great difficulties in maintaining control over the worldly leaders, who engaged more in internal warfare than in expansionist wars against pagans. In the effort to restrain and redirect Christian warfare away from Christians the Church attempted to ban certain modes of warfare. It thus embraced a code of conduct among kings and knights not to use poison, which they viewed as dishonourable, because it enabled the weak to overcome armed warriors who had invested heavily in equipment and training. In the same vein, in 1139 the Lateran Council outlawed the crossbow.
However, these were merely informal directions. The custom restricting the use of poisoned weapons in war was first codified in Article 57 of the Strasbourg Agreement of 27 August 1675, by which French and German forces, and their respective allies, agreed to prohibit the firing of poisoned bullets and to severely punish any soldier using such munition.^(2) The Strasbourg Agreement was valid for the duration of the war, during which Louis XIV tried to establish French control over Lorraine.
However, comprehensive agreements on the conduct of war between nations would not exist until the 19th century, with nations exercising the discretion of issuing unilateral rules to govern its conduct or to seek an understanding with an adversary.
^(1) G. Bühler (Translator), The Laws of Manu. Translated with Extracts from Seven Commentaries (1886)
^(2) L. Lewin, Die Gifte in Der Weltgeschichte (1920)
As u/lazarus2605 has already said, there don't appear to be any reliable sources for the French attempting to ban the 1796LC sword.
One thing that can be added is that, although Ramsey says (really, Wikipedia says, since the book is just a compilation of Wikipedia articles) that the weapon was unique:
Its blade, unlike other European sabres of the period, widened near the point.
this is simply wrong, since there were other European sabres of the period which also widened near the point. In particular, hussar swords in common use in Eastern Europe often widened at the tip. These hussar swords were the inspiration for the 1796LC, the designer John Le Marchant having served alongside Austrian hussars in the Low Countries in the early 1790s. One example:
Such swords descended from earlier wide-tipped swords, which were used in Eastern Europe, notably in Poland, already in the 16th century:
https://commons.wikimedia.org/wiki/File:Sabel_-karabela-Livrustkammaren-_43161.tif
https://commons.wikimedia.org/wiki/File:Sabel_-Livrustkammaren-_787.tif
While some of these swords show plenty of Ottoman influence, with similarities to Ottoman swords such as this one:
there are other, more purely European, examples of wide tipped swords, such as this wide-tipped 17th century German sword:
The 1796LC sword was not some special new wonder-sword, extraordinary in its brutality, but a further evolution in a long tradition of wide-tipped sabres. In particular, the French already had experience of similar swords in Austrian service, and would not have found the British sword particularly surprising in its effect. While the effects of such swords - generally excellent cutting weapons - can be gory, it should be remembered that other weapons common on the battlefields of the time, such as muskets, cannons, and grenades, were quite capable of producing injuries equally, or even more, horrific.
References:
The Royal Armouries on the 1796LC, and a nice example thereof: https://collections.royalarmouries.org/battle-of-waterloo/arms-and-armour/type/rac-narrative-289.html