The 6th Mass. and 6th Illinois left Camp Alger on the same date, July 5, 1898, headed for Santiago, Cuba.

Arriving in Cuba, after the surrender of Santiago, both of these regiments were, subsequently, sent to invade Puerto Rico, likely re-equipped with Krag rifles.
(The land campaign in Puerto Rico lasted from July 25 to August 13, 1898, Ceasefire).

Attached pictures show a young 6th Mass. Soldier, (C.J. Duffy, Co. "C"), who went to Puerto Rico. He has a Krag, tropical uniform, and Spanish 'cockade' on his campaign hat.
(I saved this photo from off an ebay listing, a few years back).
A detail from a picture, (from "City of Canvass"), showing the 6th Mass leaving Camp Alger for Cuba with T-D Springfield rifles.
The Mass'. men seem to favor the 'Montana Peak' on their hats:

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