I would like to point out that weightite could be used in very heavy armour, which has its uses, and gyroscopes, and ballast, and anchors... It can also be coated with crystal or steel to make up for most material deficiencies it might have.
Wind is air in motion. This is not so much a matter of opposing forces as it is a matter of throwing inertia at each other. Due to its low density, the amount of air that a bullet encounters is relatively low, and thus the amount of inertia pushing it to the side is relatively low. In order to keep the mass(and thus inertia) of encountered air low, the effective relevant cross-section of the bullet should be small. This also applies to penetration, the smaller the bullet is, the less armour it needs to move in order to make a hole. Meanwhile, the bullet has its own inertia, which is based solely upon its mass.
In short, we want as much bullet as possible to pass through as little air as possible. Crystals are low-density compared to steel. That means that the same mass of crystal encounters more air due to being larger, or that the same volume of crystal is more easily veered off due to reduced mass.
There is also the argument that lighter objects move faster, and that spend less time in the air, and thus encounter less air due to the air travelling sideways and thus encountering the bullet regardless of whether the bullet is in motion. This is completely undone by the fact that a proportional increase in velocity will produce a proportional reduction in travel time and require a greater than proportional increase in force. There is also an inverse economy of scale in firing chambers and barrels. Doubling the thickness of a chamber in order to facilitate a more powerful charge requires much more material if it is applied to the outside of the chamber than to the inside, due to the greater circumference at the outside than at the inside. Thus, a smaller bullet with the same mass can have its velocity increase more easily than a lighter bullet with the same circumference, assuming that you do not want your cannon to explode...
A heavier bullet will, however, offer more resistance to being propelled out of a cannon than a lighter bullet will. Given that the bullet, even if quite heavy, will still have by far the lowest resistance to receiving force of the whole mechanism, this is basically a good thing. A slight loss of efficiency in relative power transfer is easily recovered by a much greater opportunity to receive power.
Crystal bullets would be a significant upgrade to wind-based defences against bullets. Our current primary problem is wind-based defences to bullets. Crystal ammunition would actually be bad for us, regardless of what it does to rate of fire.
Considering that our Mundanes are already limited in their rate of fire due to power shortages, it seems reasonable to assume that this is also a factor for our other cannons, given that a single wizard can contribute to multiple cannons if they are in close enough proximity. Adding to their power consumption without solving the power shortage issue seems to be a mistake.
Their antimagic only applies if they can get into range and choose to use it. Given that it will only stop lucky-strike, and they can only antimagic at medium range, it is still useful. And we can only get lucky strike working if we understand it. Spending a single revision to get a handle on a completely new field of magic is well worth it. Our previous forays into new forms of magic have been notoriously difficult. If we had gotten a competent form of antimagic resistance back when I asked for one, then we would not be having this problem. Unfortunately we got an antimagic resistance that applies only to circuits, and is a hard-counter within that theatre so will probably be nerfed under the new rules. Don't be surprised if Avengers start dropping out of the skies if they get into short-range of an antimagic field...
KPD4 is a minor addition. Do you know what the "4" stand for? It stands for "it failed on three previous designs, lets try again". Go back and take a good hard look at the KPD4 proposal and see if it makes sense that a revision with that description would do any more for us than the 3 whole designs that evidently weren't satisfactory. It has been mentioned that the hull is the reason for the poor acceleration. We need a complete redesign of the aircraft to improve its performance noteably. It still won't work, of course, Keggers rule the skies, they can make jet-engines with a single revision, our airforce will never be more than "present" at this rate, and a revision certainly won't change that when three designs didn't.
Crystal Ammunition Fabrication is a downgrade. It uses inferior ammunition resulting in less range. It increases potential rate of fire by being less energy-efficient per shot, thus reducing practical rate-of-fire in most scenarios. The only significant advantage it would see is in removing the need to handle the weapons, so aircraft could have fixed guns and no gunner, being traditional dogfighters. Given that they are difficult to fly, however, we likely want dedicated gunners regardless, so why not use them as reloading mechanisms too and save on power consumption? Summoned ammunition is a good idea, but it doesn't work if we are summoning low-density crystals using a limited power source.
ER Blastshells have the same problem of being light. They do, however, at least replace an older technology. They are very much unlikely to increase our effective range, because they will be less deflection-resistant than solid bullets, but at least the sustained thrust might lower their exposure time...
KPD4 is too little to make a difference without a really good roll and favourable G.M.. We do not want to rely upon such things, although the favourable G.M. bit has turned out well for us in the past.
Train-deployment is, as others have said, largely redundant. There is some sense, however, in providing mobile resupply stations. I am not voting for it, but still...
Barring a massively good result. KPD4