Above is a short presentation by a BAE representative brought us by NavyRecognition from the 2017 Surface Navy Association Meeting.
- 00:00–00:20 is intro.
- 00:20–01:15 discusses the electromagnetic rail gun.
- 01:15–02:30 covers the hypervelocity projectile that they expect to fire from the Mk45 5″ naval gun, the 155mm howitzer, and the electromagnetic railgun.
- 02:30–03:35 is about the Mk45 mod4 5″ and an automated, unmanned magazine designed for an international customer (It is planned for the UK’s Type 26 frigate).
- 03:35–04:42 is about the Mk110 57mm gun and a special purpose round they are developing, the ORKA (Ordnance for Rapid Kill of Attack Craft).
Below I have included a video with more detail on the ORKA round. Note this is a specialized guided round intended for use against small surface targets and inbound air targets. It should have a much higher probability of hit than the ballistic round, but is unlikely to have the full range (17,000 meters) or high altitude reach (PFHE: 24,930 feet) credited to the Mk110 because the round appears heavier than the ballistic round, control surfaces will add drag, and because of its larger size displaces some of the propellent that would have been in a more conventional round. The video claims an effective range of 10,000 meters (about 11,000 yards). That may also be its maximum range.
Chuck Hill's CG Blog 
In addition to the factors you mention, Chuck, the 3P “ballistic round” will have a shorter time of flight due to the higher velocity, and most importantly, a much cheaper cost.
We’ve talked about training and projectile cost here before with the Mk.110, and the 3P “ballistic round’s” cost was thought to be so high as to limit quantity deployed, let alone trained with. Well, if the 3P round was expensive, wait until you see the bill for these! (And on that subject, why is the 3P round so expensive?!? Pre-fragmented shell bodies have been around since at least WWI [depending on the level of sophistication we want to apply], and RF programmable time fuzes have been in America’s arsenal since WWII.)
It’s impressive the miniaturization which is being achieved. The 155mm Copperhead projectile deployed in the 80’s after 15-20 years of development, and it took another 15 years to shrink that technology to 5″ (127mm). Getting it down to 105mm or 75/76mm was never really persued, because the terminal ballistics of small projectiles wasn’t thought to be worth the developmental effort. Obviously, the small boat swarm created a threat which made the development worthwhile.
Another effect of putting this level of technology into such a small projectile, is that, in spite of continued progress at miniaturization, the electronics, battery, servos, space for the fins and canards when stowed, and the seeker all take up room, thus diminishing the warhead size, in comparison to the 3P. Not a big issue, considering the threat identified in the intent, but if other targets come into play, it must be taken into consideration.
It appears China may be preparing to test a railgun at sea. https://www.navyrecognition.com/index.php/news/defence-news/2018/february-2018-navy-naval-defense-news/5910-is-china-s-plan-about-to-test-a-railgun-at-sea.html