I was looking at the PCGS plate coins for both PR coins and MS coins.
Besides the die markers (which I can't see on OP's coin based on pics), I noticed a distinct difference in the middle of the ear which blends/fades into the hair.
Notice the top of the ear on MS coins are not as detailed as the PR coins.
Also, the first hair lock on top of the MS coin is not as detailed as a PR coin.
Now again...this was just looking at PCGS plate coins for comparison.
My first thought when I saw OP's coin was PR.
I think Grandpa was correct!
Great coin!

smat