Starting in 1996 the $.50 coin issued in the Proof Set was struck on a sterling silver (92.5%) planchet. From 2012 on they were struck in fine silver (99.99%) planchet.
I will show now two of these coins.
The first was part of the Coronation Coin and Stamp Set. It commemorates the Queen's Jubilee. Its weight is 9.3g with 92.5% silver purity and Proof finish. The mintage was 14,743 units.
The second is a "normal" coin from the 2018 Premium Proof Set. Its weight is 9.4g with 99.99% silver purity.
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