Interesting grips! I would bet they are Mexican made, and hollow. And I would expect them to be Sterling Silver rather than pewter. Take them to a plating shop and ask them to check them with their X-ray fluorescence (XRF) analyzer, or other method they may use. This method is non-destructive.
I did this several months ago with a ring that my then high school girl friend, 27 years later my wife, had given me in 1961 as a token of going steady. I had left it in a silver cleaning solution overnight and thought it had lost its plating, it looked terrible! I wanted to have it re-plated as I expected it was a base metal alloy originally silver plated, but the shop confirmed it was Sterling. I was very pleasantly surprised as the ring had only cost something like $2 when she bought it. The shop foreman volunteered to test it, and I was not charged! I lost her in Sept, 2019, and that ring is one of my most highly prized possessions!