"A coin dealer, who once had strong connections to the
RCM, once told me that only the proof-like and specimen strikes from 1967 were .800 silver, the business strikes were .500 silver. Of course, that is heresay, but I am not about to start zapping rolls of 1967 10-cents to prove it one way or another. Given the mintage of that series, I would have to spend days with the XRF zapping hundreds of coins to get a 95% confidence interval of that data..." -SPP-Ottawa
It's interesting you say that about the proof-like/specimen strikes vs. the business strikes. I picked up two of these dimes from a dealer, both had been circulated/touched by human hands, yet one is proof-like and the other is considerably dull. The proof-like "80%" version still has sharp detail on the crown (even though the obverse is dull on it), and the mackerel. The other "50%" one has a tiny bit of luster left, but the crown and fish are not as sharply struck. I do realize they're both not in pristine condition and am just throwing this out as an opinion, but side-by-side, there is a difference with each obverse even though they're both dull.