In 1968, proof coin production moved from the Philadelphia Mint to San Francisco and proof coins gained the “S” mintmark. ... In 2017, the “P” mintmark appeared for the first time on circulating cents. This change was only for the 2017 issued cents, in honor of the U.S. Mint’s 225th anniversary. Your 1966 NMM could actually be a proof, from the Philidelphia Mint! I have a whole roll of Franklin Half Dollars with all the same mirror luster as your coin. They all came in an uncirculated roll that I bought from a dealer with full lines on the bell.
Since I started this post I have compared this coin at other '66 SMS Kennedy halfs. They all have a proof like finish. I agree this loose SMS that has a better surface than the others that I can it compare to. Everyones imput is appreciated.
When nothing else to compare to, side x side in hand, etc, (photos don't do it) yes, the SMS half, et al, can often "look" proof, but when compared in person side-by-side with a good/true proof, there's no comparison in my opinion.
Here's a pretty good read on why there were no mint marks from 1965, 1966, and 1967! https://en.wikipedia.org/wiki/Coinage_Act_of_1965
I can see we got folks here to read up. And, when Google isn't your friend, Make sure that you use that search bar up in the right corner of the page.
Johnson screwed up a lot of things in the US. Now we know who was responsible for this clad coin junk. Let’s go LBJ!!!
And no Kennedy halves were minted in Philadelphia between 1964 and 1971. (Well they did strike 1964's in 1965.)