The weapons we have today are very well engineered (cheap, reliable, understood tolerances/ranges, etc). As such, where railgun tech will be used is in limited cases as compared to the well developed cheamically launched projectiles. That means that there are less cases where the railgun can be used and then learned from. Especially with weapons, you need real life testing in order to understand the engineering issues, as lab testing is generally forbidden due to loss of human life. Hunting deer and boars will only give you so much. Fortunately, we humans don't go to War too often these days (though this is very debatable to a lot of real people). Unfortunately for railgun engineers, that means there is not a lot of real world testing in the panic that is a battle.
Like, fire one of these railguns that are ship-based in rough seas at a hostile target that is shooting at you too. There's smoke, flak, little wires, mist, spray, etc in the air that can gum up the gun and jam. Does firing one of these things in a storm have interactions with lightining effects? How does that big of an EM field affect sailors over time, like the concussive blasts affected sailors previously?
But that's already something that a person can think of. It's the stuff you cannot think of that are the main issues. When the panic sets in and the battlefield is very live, what happens that will affect the armaments that you did not think of?
