I just received a 1946 Walking Liberty I had sent into one of the big PGS. It didn't come back at what I was expecting. I'm going to post the photos and would approcate any grading opinions. Once I get several I'll unveil the grade and the company, and the discussion can continue from there.
It's not MS anything, it's seen some circulating for sure. Maybe AU 55. Those scratches in the right obv field might give it a details designation. That depends on severity of them, it's tough to tell from your pics.
I see one of those coins on the confusing "AU58/MS63 slider divide", which could go either way. I'm gonna give it the benefit of the doubt and say MS63. Heck, I'll even go all liberal and guess MS64, since you said you were surprised. That would surprise me, a little, but it was my initial impression at first glance. Pleasant surprises happen for me about as often as unpleasant ones, in the TPG submissions game. Hopefully that's what you got here. I agree with @ToughCOINS that it looks like present-day ANACS plastic. PCGS would have had noticeable clear "grippers" and NGC would have those ghastly, intrusive white prongs I hate so much.
I'll say MS64. I might have gone MS65 except for the right field obverse scratches pointed out by @Nathan401 and the scratches on the reverse on the eagle's left wing. Not sure in my "newbieness" if they would cause a "Details" designation.
Strong strike, good luster. Average eye appeal and some distracting contact marks in the field of obverse and possible friction wear on some high points on the reverse. 62?
First impression made me think MS 63, but I believe there is wear and they went AU 53 (which would be lower than I would expect).