I'm at MS62/63 on this one.
1881-S is a Morgan date/MM that can look unreal in quality, and it takes an average MS65 to make a MS64 grade on this one and a few others

It all depends on the luster (less any contact marks) which I imagine is subdued by the photo lighting rather than more than it looks in hand. MS64 in almost any other date/MM Morgan though. 1881-S seem to be held to a higher grading standard by the
TPG's (since there are so many great looking ones, along with 1879-S) IMO.
Here's some interesting numbers from David Bowers and PCGS:
-The five most common MS-65 or better
Morgan dollar issues are:
1881-S: 150,000 to 250,000 (the most common
Morgan dollar in this grade)
1880-S: 125,000 to 175,000
1885-O: 100,000 to 175,000
1879-S, Third Reverse: 100,000 to 150,000
1882-S: 100,000 to 150,000
The following varieties all have estimated minimum populations of 100,000 or more coins in MS-64 grade:
1881-S: 400,000 to 600,000 (tied with the following most
common
Morgan dollar in MS-64 grade)
1885-O: 400,000 to 600,000 (tied with the preceding)
1884-O: 350,000 to 500,000
1887: 350,000 to 500,000
"Buy the Book Before You Buy the Coin" - Aaron R. Feldman - "And read it" - Me 2013!
ANA Life Member #3288 in good standing since 1981, ANS, Early American Coppers Member (EAC), Colonial Coin Collectors Club member (C4), Conder Token Collector Club member (CTCC), Civil War Token Society (CWTS) member, Liberty Seated Collectors Club (LSCC) & Numismatic Bibliomania Society member (NBS), USMex, Member in good standing, 2¢ variety collector.
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http://goccf.com/t/140440