stamping mill vs stamp mill

stamping mill and stamp mill both are nouns.

Word	Noun	Adjective	Verb	Adverb
stamping mill	Yes	No	No	No
stamp mill	Yes	No	No	No

As nouns, stamping mill and stamp mill are synonyms defined as:

stamping mill and stamp mill: a mill in which ore is crushed with stamps

stamping mill (noun)	stamp mill (noun)
a mill in which ore is crushed with stamps	a mill in which ore is crushed with stamps