I've thought of a few ideas for primary weapons that seem interesting to me, and I thought you guys might like to read about them. Of course, some might have already been used; I'm not even close to having played all the campaigns out there. But it's struck me how many potential gameplay gimmicks for primaries there are (and how lackluster the retail ones are).
1. Shrapnel sabot gun. Kind of like the primary equivalent of a cluster bomb -- it's a high-velocity, low-ROF weapon that shoots a single shell. On impact, it fragments into a Sidhe-like blast.
2. (Actual) leech cannon. Fires a beam that drains energy from hostiles and adds it to the wielder's ship. That might actually make it worth using, in conjunction with a heavier weapon.
3. Antimatter projectile cannon. This is less about the weapon concept itself and more about the surrounding balance issues. When I played Freespace Blue, something about the modified Morningstar -- probably the impact shockwave it generates -- made it feel as though putting a pair of them on something like a Pegasus let it hit above its weight. I tried to think of how a weapon could be designed specifically for light fighters, and I got this.
It's a ballistic weapon, with a moderate-to-high fire rate, absurd damage, and a short range that makes it best used with a highly-mobile ship. The actual rounds are tiny -- because you don't need much antimatter to do a lot of damage -- but there's a cap on how many can be carried on one ship. I thought about how to justify that with a fluff explanation -- I'm not sure how much difference it would make to have a stupidly excessive amount of antimatter accidentally detonating inside your ship rather than just a moderately excessive amount -- but it turns out that justification already exists in the Tsunami techroom description, which is probably why I was thinking about it to begin with.
Anyway. It's designed to be absolutely lethal when used with something like a Pegasus or Loki, but of limited utility on heavy fighters, since they can't actually carry any more ammo for it than smaller ones can.
4. The tractor gun. My personal favorite. Low damage, but extremely high range and velocity. It's like a backwards Morningstar -- it fires negative-mass projectiles that, upon impact, drag the target back toward the shooter. Oh, and it propels you forward, so it's best used with a ship that can generate reverse thrust. Not that effective on its own, but it doesn't need to be -- you sit next to an Aeolus with this thing and reel in enemy fighters to get chewed apart by the triple-a defenses. Or just cut out the middleman and stick it on a turret.
Of course, the question is if it's even possible to give a projectile negative mass without the game ****ting itself. I'm pretty sure the effect could be scripted in a pinch, though.