@Undftddj here they are using iron bullets, instead of the commom lead bullets of real life. Iron has a melting point of 1538ºC.
In fact, we know they are not using lead bullets, because lead is not magnetic.
And to aswer my own question, ``wouldnt be better to just heat the bullets to 750ºC then shoot it?``
No, bc the gunpowder ignite around 430ºC, making this tactic inviable