Originally Posted by
stephen m weiss
This is a good read. Bret comes closest to my view on this. I am new to cb and reloading in general, but did metal failure analysis in extreme environments and motion for 30 years. All of these issues show up elsewhere in machinery failure, manufacture or assembly.
Please forgive my nerd-speak and understand that I am just excited with this really fun topic. I do not intend to imply that ed-ja-ma-cation is in anyway a substitute for experience, especially in a topic like this one. These are musings, written like I write for fun, and I prolly sound like a pedant or some other horrid ting.
With the lead bullet, the situation is so much more complicated. The lead is already very close to its melting point so addition of heat from gas and rifling friction interact with the above-yield stress state at the rifling to push the total lattice energy above the melt enthalpy.So the contact point lead leaves the area, allowing cocking.
It is so unpredictable because all these exponential effects are combining to eat away at the tiny remaining lattice stability of the lead. And when pushing a rod from the back it is always hard to predict when it will go sideways. The driving force, the powder explosion, is an instability in itself, and varies a lot from shot to shot, day to day, powder to powder. Finally, while we get to hear about the caliber, length and rifling of our barrel, we usually get no information on the surface roughness or actual dimensions of the land and non-land geometry. The non-lands are the flow paths for the superheated gas and grit to rush past the bullet surface adding heat and stress.
The good thing is that all of these factors do not involve chaos, relativity, atmospheric corrosion, or radiation. That aside, mixed phase flow, contact stress and friction, dynamic thermal material property change, phase change, three dimensional stress state, and deformation dependent loading are all some of the most challenging stress analysis modelling that can be accomplished, one at a time, let alone combined.
Just my 2 cents on the really cool issue.
smw