Don McDowell wrote:[quote="76/444"bumping" up can ONLY be accomplished with the early and extreme pressure spike of Black Powder and other similar explosive smokeless powders. "
Now, my intent was to diffuse the internet propagated MYTH that boolit velocity causes leading,... and YOUR contribution to this subject is......?
A little bit of experience goes a bit further than reading comprehension.
It doesn't matter whether its black powder or Smokeless powder either one will only bump an alloy so far. How far a bullet will bump up depends on the hardness of that alloy. It's a simple thing to start testing say paper patch bullets. Use the same mold and only change the alloy. When the alloy gets to hard the bullets ceases to bump up, fill the rifling and poor accuracy combined with tumbling bullets will be the result. This happens with either smokeless or black powder charges.
You can do the same thing with hard grease groove bullets to small for the bore of a rifle. Won't matter much which powder you use, either one will get you leading and recovered bullets will show virtually the same amount of land engraving, with the recovered smokeless fired bullets showing a slight bit more of engraving due to the higher pressures exerting more force onto the bullet.
Also what often times get overlooked is the length of recovered cast bulllets, the softer the alloy the shorter they'll be, the soft alloy "bumped" up more than the harder alloy and the harder bullets will be closer to original length.
Lube is extremely important no matter what the bullet size or powder charge. If a lube does not coat the inside of the barrel to keep the bullet from "tinning" itself to the steel on it's trip down the barrel you will get leading.Once you get some leading started that chunk will continue to strip chunks from the succedding bullets, until it's sometime possible to get a string of lead 1/2 inch long out on a patch.
Alot of this is why the age old recommendation of bullets being .001-.002 over groove diameter. Going over that diameter can cause finning of a bullet whereby the base will be cupped and the grooves left in the bullet will be extended somewhat over the base like a "fin".
Where the leading is in the barrel will tell you alot about what is going on. Close to the throat alloy is to soft, and or to small, further down the barrel, the lube isn't doing the job it needs to be doing. Oft times the addition of a grease cookie or modern "wax check" will solve some leading problems. As will a good coating of Liquid Alox on undersized bullets.
Sometimes in oversized chambers you're just screwed, because by the time you get a bullet up to the size it fills the throat adequately accuracy will go to pot due to finning and instability of the bullet. Conversely chambers to small for the barrel you can't get a large enough diameter bullet to seal off the bore, and leading will be present and accuracy will be short lived.[/quote]
Good info,.... thanks.
What,... if any,... would be your difference in defining "leading" from "smearing"?