Another Weapon Reserch

[HMS Sophia]

Good luck even getting the barrel into a room for clearing.

You don't need to. A 40mm will shoot through walls. Clear the room and the building all at once

[Knife]

I don't think you need to cancel the project, just dial it down. In fact... dial. Have a dial a yield option with multiple types of ammo. If it's some sort of coil gun slinging bullets with magnetic fields, I see no reason the bullet has to fit snug in the barrel as if it needs to use rifling. I'd have a smaller projectile for standard anti personnel ammo, 4mm-6mm with the weapon having a dial a speed starting at 500m/sec or 1000m/sec and up to 1000m/sec to 5000m/sec with the option of using larger bullets for penetration.

So, something like: You slap a 4mm ammo magazine into the weapon and the rifle recognizes the ammo and presets the weapon to the 500-1000m/sec setting. Your tageting system in you're power armor identifies and classifies you're target as a human sized soft target at X range and further refines you're settings to optimal. Say 658m/sec for the 65m to target. You pull the trigger and 1/10 of a second later your target has a 4mm hole in him.

But OH CRAP, armored vehicle comes up over the ridge, so you're infantry man drops the 4mm mag and pops in the 8mm mag. Weapon automatically presets the 1000m/sec to 5000m/sec option. You're targeting system ID's the target as a hard target and further refines you're system to optimal blah blah blah. You get the point.

[TeufelIV]

There is sort of a weapon system in Anti-Material Rifles sort of similar to what your asking about.
Steyr IWS 2000 fires a 15mm APFSDS round.
Muzzle Velocity at about 1,450 meters per second
Effective Range 1000 M
Max range 2500 M

Steyr AMR

Wiki Pedia Link

World Guns link

The sabot coming away drawing

[erik_t]

Can't quite get my head round the math for this myself- but can anyone who can tell me if my gut instinct is correct, and a projectile moving at 17kps at sea level atmospheric pressure is going to superheat from air friction and burn up in very short order?

Of course. Keep in mind, too, that air resistance power scales with the cube of velocity, so the rate of heating (in watts or some other suitable unit of power) for a projectile moving at 4 kps would be eight times the rate of heating for a projectile moving at 2 kps. Do the math: if an object moving at five times the speed of sound (1.7km/s) were accelerated to 10 times that speed, it would be heating up a thousand times as quickly.

17 km/s is similar to the impact velocity of Earth-crossing asteroids. At that kind of velocity, the rule of thumb for rock is that it will be vapourized by the time it passes through a column of air roughly equal to its own mass. A projectile made of various super-materials could last longer, of course, but one should make no mistake that we're dealing with a huge amount of heat.

Frankly, Mike, you should be pleased. Someone finally figured out how to make a plasma* cannon!

Assuming a nose radius on the order of 100um, which is probably excessively generous, the usual back-of-the-envelope methods would suggest a stagnation point heating rate on the order of 66GW/m^2 (cf total freestream enthalpy flux around 176 GW/m^2). This does not compare favorably with the heat of vaporization (atomization, first, second, third ionization...) of tungsten.

Tungsten vapor, apparently

[Darth Wong]

Heh heh

Unfortunately, I think most peoples' ideas of atmospheric drag heating are based on movies, and in movies, things moving very quickly through atmosphere heat up and maybe melt around the edges, but they don't vapourize.