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Originally Posted by Dave Waits
Doc, how can the powder used have any effect on leading unless you were driving it near max charge? Velocity is what causes leading.
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Dave, I am not an expert on such matters, so I would refer you to this page:
http://www.lasc.us/Fryxell_Book_Chapter_7_Leading.htm
There are quite a few different causes of leading, and if velocity were the sole cause I would not have had any leading because my velocity was pretty low! I assure you I
DID have leading.
I bring this paragraph to your attention:
Quote:
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The other issue here is that the slow pistol powders reach their pressure peak when the bullet is an inch or two in front of the forcing cone, when the bullet is fully supported and contained by the barrel. Sealing and lubrication are fully functional in this environment. The fast pistol powders reach their peak pressure when the bullet is in the throat or traversing the cylinder gap. This is fine if the load involves modest pressures, but if a plain-based cast bullet is subjected to magnum pressures as it crosses the cylinder gap, then serious leading problems can arise. The take-home lesson here is to not use fast powders for magnum pressure levels in the first place! Just match the powder to the pressure curve.
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Keep in mind these were light loads, right at the power floor for CDP class IDPA. My (non-expert) opinion is that peak pressure was not being realized with HP-38 quickly enough, causing some leading near the chamber in the barrel due to gas cutting of the bullet. Switching to a quicker powder caused the bullet to "bump up" quicker, resulting in full obturation sooner.