I'm so glad to find this thread, I ALWAYS thought the same thing! I've got a rifle, I'm looking down the bore of a 75mm tube, what the heck why not? Aim for the top rim to account for sight offset, and say a little prayer, which that sniper already had covered!
And what might happen, if lucky, would be that you could in fact damage the fuze! If the round does not blow up in the chamber, then perhaps the fuze will be damaged so it will not blow up on impact, and it will blow a hole in the stone structure. You'd have bits of flying rock stuck in you, and you'd be super deaf from muzzle blast, but if you could still see you'd have a chance to get out of the tower before they reloaded. Maybe. Ok so you'd be dead from muzzle blast. Good point.
As for the quoted post, I believe that nothing actually melts on impact. OK I have heard of tankers in WW2 who got burned by little bits of molten lead from MG fire that hit their glacis and flew in the vision port, but that's all. When a bullet hits a steel plate I don't think the metal melts, it just flows like it was melted. But it's not melted. Like when you put a really heavy weight on the end of a steel pole, it will bend like it's melted at that one point, but it's not actually melted - it just flows. Plastic deformation iirc, when the elongation to break is exceeded.
So when a bullet hits and metal is forced outwards around it, making a crater, it's just pure brute force making metal flow like toothpaste. And when shaped charges hit armour they do the same thing, just at 10,000m/s instead of 1000m/s.
"Jim Keenan
I think a lot of people have a vast overestimate of the capability of small arms armor piercing bullets and a vast underestimate of the hardness and thickness of tank armor.
Just FWIW, AP bullets like the .30 and .50 do not actually penetrate armor like they penetrate wood or sheet metal. When a bullet is fired, it has a certain amount of energy, the same energy you see in ballistics tables. When a bullet strikes a steel plate, that energy is instantly converted into heat. The heat melts a part of the plate, creating a shallow hole and raising "splashes" of steel that freeze instantly, looking like those strobe photos of a milk drop. The AP core remains intact and drives through that molten steel (if the plate is thin enough) and does damage behind the plate. In thicker and hardened plate, it can create a shallow "dimple", if it has any effect at all.
But no WWII or later tank armor is thin enough to be penetrated by any AP bullet using that principle. Tank and artillery anti-tank shells use the shaped charge principle, as do weapons like the RPG and "Bazooka". AP rifle and MG ammo was issued in combat in WWII not to stop tanks but to shoot through the sides of trucks and other light vehicles as well as thin cover of other kinds. In most cases, those did not offer enough resistance to even cause the AP to function; the heavier bullet simply gave better range and penetration in the normal manner.
As to shooting down the barrel of a tank cannon, the shell would not be bothered a bit by a small caliber projectile wedged in the bore. The bullet would be simply "ironed" into the bore. Some types of fuses might be touched off by a bullet, causing a bore premature, but the odds are so high as to be ridiculous.
Jim"