I can't help but feel that ever since lasers got their spinal mount option those two weapon systems have fallen behind in usefulness compared to them.
They still have their niche where they are slightly better then the laser, but even combined with their cheaper research (if you want your laser to reach all its potential) its just not enough to make me want to use them when compared to the allmighty lasers flexibility.
Compared to the meson, gauss, plasma or HPM which all still have highly specialized areas that set them apart from the laser or where they are clearly superior, the PB and RG are "just" pure damage weapons for long or medium range respectively, both areas where the laser is also at its strongest.
Therefore I suggest a new line of research for each.
Railgun: Advanced Alloys. New and improved heat resistant metal alloys. This research has 3 levels that reduce the atmosphere reentry penalty to 0.85, 0.70 and 0.5; so a fully researched railgun would only lose 50% of its damage when shooting at a 1.0 atm planet (They'd still be useless against 2.0 atm, or even earlier considering that damage <1 gets rounded down to 0).
Particle Beams: Another 3 level research. Each level increases the damage the beam deals to interior systems by 25%, meaning a strength 4 beam with level 3 of this research would count as a strength 7 weapon when rolled against a components HTK. I'm sure someone could even come up with a good name for this, I can't though
Both of those researches should be somewhat expensive to research (8000, 16000, 32000 RP?) for a young nation but free when included in the actual weapon. (Added automatically to every weapon designed after the research completed. Kinda like improved agility or warhead research for missile designs.)