David, for the 1:16 twist, a 1.400" bullet from my Brooks mould, is stable to 1,000 yards.
 
Pedersoli did not have a specific bullet mould available for the fast twist .40 Gibbs, when rifles were first released. Have not heard differently, to date.
 
Peepsight, ... should be able to provide bullet length for his 318 grain .40 caliber Pedersoli mould.  
 
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"So, at short range (100-200yds) does the 1 in 24 twist have any advantage over the 1 in 16." �David
 
Advantage: It could save a shooter around 20 grains of costly blackpowder and 100+ grains of lead, per shot. Additional advantage, a 318 grain bullet should shoot flatter, with less recoil.
 
Disadvantage: If someone purchases the 1 in 24" twist .40 Gibbs for short range shooting only. Then at a later time, decided they wanted to shoot creedmoor matches, the slower twist would not stabilize a heavier bullet properly.  
 
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