As of today, melt value for silver dimes is $3.10; for quarters, 2.5x dime value or $7.76; and for halves, 5x dime value or $15.51. The math for this is consistant at 31.03 x face value. However, for dollars the melt value is $33.18 per dollar (33.18 x face) or almost 7% higher than smaller silver coins. Why would this be? They're all 90%Ag / 10%Cu. Ref. www.coinflation.com
Because 90% Silver Dollars have slightly more silver than $1 face value of 90% silver dimes, quarters, and halves. From the Red Book: Silver Content Dime 0.07234 oz Quarter 0.18084 oz Half 0.36169 oz Dollar 0.77344 oz So a Quarter has a face value 2.5X that of a dime and a silver content 2.5X that of a dime. A Half has a face value 5X that of a dime and 2X that of a quarter and a silver content 5X that of a dime and 2X that of a quarter. But a Silver Dollar has a face value of 10X that of a dime and a silver content 10.69X that of a dime, a face value 4X that of a quarter and a silver content 4.28X that of a quarter, and a face value twice that of a half and a silver content 2.14X that of a half. Silver Dollars simply contain more silver per unit face value than dimes, quarters, and half dollars.
I believe dimes, quarters, and halves all have some ratio. Also, just check Coinflation and you'll see they're each worth 3103.35% of face, but dollar coins aren't.
Then dealers or wholesalers who buy junk silver and pay based on face value pay on the lower value and make out when buying dollars.
Silver content for a dollar, 90%, is .77344 oz. Silver content for a dime, 90%, $1 value is .7234 oz. Silver content for a quarter, 90%, $1 value is .72336 oz. Silver content for a half, 90%, $1 value is .72338 oz. As you can see the difference in silver content for $1 face value of the smaller denominations is quite a bit under the dollar coin itself.