https://www.timelessmyths.com/history/triangular-bayonet/
The following are some key points to remember regarding triangle bayonets:
Triangle bayonets, as the name implies, are triangular bayonets that were initially developed in the 17th century in France. They were an improvement over the plug bayonet, which had the drawback of preventing the gun from being fired when it was attached.
The fundamental advantage of the socket and split-socket bayonets with triangular shapes is that they allow the musket to be fired while the bayonet is attached to the gun.
Many believed that the triangular bayonet Geneva Convention of 1949 banned triangle bayonets because the wound they make causes undue pain even after the battle because the broken skin and the wound from triangular bayonets were impossible to stitch; however, only bayonets with serrated edges were confirmed to be banned.
Even though triangular bayonets are hardly used today, they still have value, especially those that are from the previous wars. They can cost as much as a thousand dollars to less than a hundred dollars, depending on the specific type.
My 45-70 has such a bayonet. A long one.