I wonder what the exceptions were, since I remember that in 0.31.25 melt yields were roughly in line with materialsize / 10.
It's funny, I had checked the wiki before dusting off my plans for my bolt splitter since the 34.05 / 06 ment I was going to need quite a bit more metal, find someone seeing some strange behavior, and after a little testing turns out I don't need the bolt splitter after all .
Ammo has never melted down based on material size (it still doesn't) - it just takes the stack size, divides it by 10, then adds 1 to get the number of tenths-of-a-bolt returned. Thus, bolt splitting has always worked for creating free metal.
As for stuff like weapons and armor, prior to 0.34.06 they were all fixed - all types of body armor (plate AND chain) yielded exactly 0.8 bars, all weapons/pants/shields/trapcomps gave exactly 0.5 bars, and all helms/boots/gloves gave exactly 0.3 bars. There was also the rather interesting claim that buckets were the best for training blacksmiths because they melted down to half of a bar (for a 50% yield, compared to the 33% yield for other furniture), though anyone with 5 minutes of testing would have immediately noticed that buckets always melt down to a
full bar - still the best, obviously, but much more compelling.
Furthermore, nobody ever bothered testing melting coins, since if they did they would've found that a stack of coins, which costs 1 bar to mint, melts down to
1.1 bars - all you need to do is mint 10 stacks of coins and then melt them down to get a free bar of that metal, making the bolt splitting trick rather pointless (since it doesn't require any special setup
and works on all types of metals other than pig iron and bismuth).