pellet vs musket ball

pellet and musket ball both are nouns.

Word	Noun	Adjective	Verb	Adverb
pellet	Yes	No	No	No
musket ball	Yes	No	No	No

As nouns, musket ball is a hyponym of pellet; that is, musket ball is a word with a more specific, narrower meaning than pellet:

Other hyponyms of pellet include BB, BB shot, bird shot, buckshot, duck shot, grape, grapeshot, ball.

pellet (noun)	musket ball (noun)
a solid missile discharged from a firearm	a solid projectile that is shot by a musket
a small rounded mass of a substance