https://www.youtube.com/watch?v=2FoWpog5KU4
That is the single stupidest thing I have ever seen. Absolute crime against engineering. Not completely relevant here, since the Hi Point is a blowback gun, and they're relying on a freaking hose clamp to keep everything together. Call me crazy, but I think Browning could do better than that
Oh yeah, and the welding mask & apron with fingerless gloves & bare forearms was nice touch :banghead:
The reason for this was never made clear, but it was said that if the bullet had been allowed to move, even the slightest little bit, disaster would have ensued.
A body in motion stays in motion, a body at rest stays at rest, therefore the bullet never moves; it is not the bullet you must move, but yourself
. No, a body moves if a force is applied --such as the pressure in a breech-- and can apply a force itself if it contacts another body that resists its motion. When a bullet is allowed to accelerate before reaching an obstruction, it gains sufficient kinetic energy (or momentum, they're all the same in the end), that when its motion is resisted by a stationary object, the force imparted to both bullet & obstruction is sufficient to violently deform the bullet outward against the barrel walls. So not only is pressure acting on the walls (likely higher than normal, since gas expansion to lower pressures cannot occur) but the pressure of the crashed bullet driven to expand by its own accumulated kinetic energy (or momentum, or inertia, they're all the same).
So violent is the collision of the bullet even after a short period of movement (the acceleration of a bullet is incredible, and high velocities can be reached in a mere fraction of an inch) that the material properties/strength of the solid lead are brutally exceeded beyond resistance, and it essentially becomes a fluid, squishing outward equally in all directions. The deforming metal is actually liquified in the areas where there is the most deformation (the atoms in the crystal matrix scrambled like a DQ Blizzard) and a tremendous amount of heat is evolved in the process of breaking those crystal lattice bonds. Eventually, the bullet has completely conformed to the gap between the obstruction and the breech pressure driving it, and can no longer dissipate any of its kinetic energy by deforming & breaking the atomic bonds of its crystal lattice structure. At that point, the only place for the kinetic energy to go is directly into the materials resisting it, heating the obstruction and barrel walls rapidly (and IIRC, isotropically, meaning a near-perfect heat transfer) potentially to the point of critically weakening or even melting them.
So, you have the following acting on your poor barrel;
-Elevated breech pressure (likely not higher than peak for most obstructions down the barrel a ways)
-Compression of the slug being driven outward
-Thermal energy dump from remaining kinetic energy
The barrel can then dissipate these forces one of several ways;
-Elastic deformation (flexing those atomic bonds in its crystal lattice structure, momentarily)
-Plastic deformation (tearing those atomic bonds, but reforming them immediately in a permanently shifted configuration --a goose egg swell)
-Phase change (not necessarily melting, but the decomposition of carbon/iron crystal structures that give steel its great strength)
-Rupture (permanent, catastrophic tearing of crystalline atomic bonds, cascading through the grain boundaries of the metal)
Both elastic and plastic deformation generate heat (the latter much more so), that heat is what precipitates phase change, that phase change rapidly degrades the threshold at which the other failure modes occur.
So the real killer is ultimately heat, unless you're talking a detonation or something that goes straight to rupture (think 357 cylinder kaboom). The main contributor to that thermal load, is the kinetic energy portion of the equation. Obviously the pressure and solid-lead expansion are not sufficient to damage the barrel, since the at-rest bullet is initially acted upon by a pressure that rivals the ultimate peak pressure attained, when everything is operating properly. It is not until the bullet is having to fight its own kinetic energy that it is pushed outward to the point of failure, as seen every time a bullet strikes a rigid target.
It would be interesting to try to isolate these effects, to see which causes failure first (i.e. which is the strongest in a squib situation).
-Fire bullet into a cavity matching its profile cut into a thick-walled cylinder at higher velocities until deformation & rupture (and compare to internal ballistic velocity profile of barrel to determine when KE alone will cause a rupture from obstruction)
-Fire blank cartridge in obstructed barrel at higher pressures until failure (and compare to internal pressure profile of normal charges at different squib locations to determine how close the stuck bullet must be to the new one for this failure mode to dominate)
-Compress lead bullet inside barrel section between tight-fitting hydraulic rams slowly until rupture (compare to velocity and pressure charts, together with results of experiment 1 & a lot of math & metallurgical knowledge, and I think it should be possible to separate the breech pressure, bullet swage pressure, and pure thermal effects as they contribute to failure, so you could see how each stacks up for a squib located anywhere along the barrel)
I know for a fact the kinetic energy effects will be lowest at the chamber-end, to the point they are near-zero for the rigid-bullet scenario posited in the OP.
Someone else do this for their dissertation
Oh, and sorry to everyone that it isn't a super-simple explanation ("the bullet melts the barrel" is potentially an accurate way to describe it, but it also omits a lot) but high energy plastic impact mechanics with multi-phase effects is serious super-science, that I can really only guess at (seems more complicated than hypersonic aerothermochemistry, I'll put it that way)
TCB
PS- this also explains how/why heavy, hard, fast moving projectiles like DU APFSDS are so hard to stop with conventional armor; all that heat energy dissipated by squishing the bullet or squeezing outward is resisted by the projectile material's own strength, leaving every last bit of that kinetic energy to be focused straight ahead, dumping an extremely high value of kinetic energy (because of the great sectional density of rigid rod-penetrators) into the target material at such an excruciating rate (4000fps is darn near instantaneous when it comes to how fast steel can conduct heat away safely) that the plate armor is simultaneous melted & punched through by whatever part of the penetrator hasn't vaporized under the stresses itself. It makes total sense that the only thing that could possibly react fast enough, and with enough force, to slow or stop the demonic thing is a high explosive pointed in the opposite direction (reactive armor plate)
