Kinetic anti-ship attacks
First, there are suggestions for a kinetic warhead to be used against Honorverse ships. The idea (as I understand it; I haven't really been participating in the thread) is that it would use an Orion-type drive, with a nuclear warhead to propel a relatively small, super-dense projectile (I think tungsten had been suggested). The device would be fitted into some standard missile body -- I think counter-missiles were suggested on the theory that they go slower than shipkillers and would therefore give more time for a passing engagement shot with this "kk" warhead. Detonation range would be standoff, but just barely -- I think a range of only a couple of hundred kilometers have been suggested -- because of the need to get the slower-than-light slug close enough to tage the target at all. Objections to it have been manifold. They include arguments that the amount of energy the small slug would deliver would be far less than the energy of an entire missile; that no missile is going to survive to that short a standoff range; that there's no way to get the slug through a sidewall; that targeting said slug would be a bear; and that even on a "down- the-throat" shot, the ship's particle shields would significantly degrade the weapon's effectiveness.
Let me get this straight. Someone wants to use a kinetic weapon in ship-to-ship combat?
The short version is that I don't see any way for this to be a practical proposition. The notion is elegant enough, but it sounds like something a war gamer would come up with, rather than a practical weapon of war. (Please remember that I used to be a war game designer, among other things.) First, the fire control for something like this definitely would be a real bear. Given the velocity of Honorverse missiles and warships, the amount of time you'd have for your kinetic projectile to acquire the target and fire would be very, very short. From what I've read about the Orion drive, I don't believe you're going to get pinpoint accuracy is one a nuclear-explosion-driven projectile under the best of circumstances. You're certainly not going to get enough of it to make hitting an Honorverse ship a very practical proposition. And you're not going to get one of these through the sidewall of a ship, whatever you do. If you're talking about using a solid slug as your projectile, you're not going to have sidewall penetrators. Without those, your slug is going to go "splat" (very enthusiastically) the instant it hits the sidewall. For God's sake, look what happened in Honor of the Queen! The only way that this weapon would be remotely practical (from the perspective of avoiding sidewall, at least) would be employed in a "down-the-throat" or "up-the-kilt" shot, and you'd have to be approaching from either directly ahead or astern on a relatively shallow approach angle if you were going to generate sufficient side vector. You'd also have to be very, very close. Without the exact acceleration figures, I can't run the numbers, but I'd guess that a range of more than, say, two hundred kilometers at pusher-bomb detonation would be completely impractical. And if you could get warheads that close to an Honorverse warship, then laser heads wouldn't need to be 30,000 kilometers from their targets when they detonate. Against modern point defense, there's pretty much no way in the world you're going to get this weapon close enough to a ship to work. Even if it were practical, I can't see why anyone would want to use a weapon which would effectively be smaller and weaker than ones already available. Specifically, if you want to use some sort of a kinetic weapon, then simply use a standard missile fitted with a sidewall penetrator. Without an extremely unlikely tactical advantage of some sort (similar to the one Rafe Cardones managed to generate for himself in Honor of the Queen), you're not going to get it close enough to attack the sidewall, anyway, but if you could, then slamming the target with a projectile which masses better than seventy tons would seem to me to make a lot more sense than trying to hit it with this "sub-caliber" slug.
I'm not sure where the counter-missile comes in. If I'm understanding you correctly, the suggestion is that counter-missiles are slower than shipkillers, which would simplify the targeting solution for the kinetic slug. The problem is that counter-missiles don't have room for a slug and its propelling nuclear weapon. Even if they did, their acceleration rate is actually higher than that of a standard missile. Their endurance is much lower, because of their overpowered drives, so their effective range is also lower than that of a standard shipkiller. Even against something like a LAC, where type-[on]-type combat is probably going to take place at shorter ranges, I can't see anyone in the Honorverse giving up the range of a standard shipkiller in order to use magazine space on something as problematical, at best, as this weapon.
As far as the effectiveness of a "down-the-throat" attack on a major combatant, the particle shielding definitely would present difficulties. I'd have to run the numbers, but the particle shielding is basically designed to handle collisions with solid objects massing up to about two metric tons at velocities of up to 60% of light-speed. More massive objects can be dealt with it lower velocities, and as the velocity rises above .6c, the size of the object the system can handle goes down. There is, however, a reason warships mount massively redundant point defense to cover the bow-aspect of their wedges, and a reason besides the need to engage an enemy vessel for mounting the most powerful chase weapons possible and mounting them in multiple numbers, instead of simply settling for the biggest, nastiest spinal mount weapon you can cram in. When an object too large for the particle shielding to deal with turns up, it is automatically engaged by the ship's point defense and -- if the ship has been cleared for action -- its chase energy weapons, as well. And the fire control on those systems is designed to engage targets coming in at better than 80% of light-speed. and they're also designed to begin engaging them at ranges in excess of 200,000 kilometers. So, I doubt that you'd be able to get your warhead close enough to score a hit before detonating, even if the slug were massive enough to punch through the particle shielding in the first place. Obviously, you'd have a better shot at scoring a hit with an "up-the-kilt" shot, where the particle shielding wouldn't be a factor except for the minor point that the after end of the ship is designed to be the forward end of the ship when the vessel is decelerating. Which means -- you guessed it -- that the stern hammerhead is equipped with exactly the same sort of massively redundant, space debris-killing energy weapons and particle shielding as the bow. So, if this sort of weapon was known to be out there, the Skipper would simply be sure that he had his particle shielding up at both ends of his wedge, and his debris-zapping armament would do the rest.
Given the size and expense of a MDM, I can't see anyone mounting this type of warhead on one of them. If it were practical to put it on something the size of a counter-missile (which I don't believe it would be) and if it were possible to generate a hit (which I don't believe it would be very often), then someone particularly fond of gadgets might carry a few of them in his magazines. I can't imagine why, given that the chances of actually hurting someone with it are so remote, and no one in an Honorverse navy would throw away a delivery system which could get a laser head into effective standoff attack range on it.