There’s a great Japanese movie (can’t remember the name) where a Japanese force armed with cavalry and spears and swords and bows comes up against another Japanese force armed with primitive firearms.
In the movie, during the battle, they keep the camera on the leaders of the force with the old weapons.
They can’t believe what they are seeing.
The battle ends and the camera pans over the slaughter caused by the firearms.
Kagemusha.
http://www.imdb.com/title/tt0080979/?ref_=nm_flmg_wr_16
https://en.wikipedia.org/wiki/Kagemusha
“Now in full control of the Takeda army, Katsuyori leads the counter-offensive against Nobunaga, resulting in the Battle of Nagashino. Wave after wave of attacking Takeda cavalry and infantry are cut down by volleys of arquebus fire from Oda troops deployed behind wooden stockades, effectively eliminating Katsuyori’s army.”
I suspect you’re referring to “The Last Samurai.”