I think Plasmacraft is about due for a weaponry overhaul. This is the post I made on the Plasmacraft thread on minecraftforum: (wall of text warning)

"I'm playing with this mod, buildcraft, and industrialcraft on my SMP server. I was wondering, what's the deal with all the different costs on the guns? The laser rifle is essentially free, and arguably better than most of the other guns. All of the other guns have fairly high resource costs considering their very low durability (especially the laser shotgun). What's the reasoning to all of this? The laser rifle I think is the fairest of them all. It still takes awhile to make the parts and ammo, and it doesn't last too long in the field. The limiting factor of this gun is that you can only carry so many replacements in the field. The Rail Gun has a pretty modest recipe, but you have to consider it essentially fires iron bars. That's extremely expensive. I guess for PvP it's not all that unbalanced.
The Plasma rifle is the most expensive. A diamond, really? for a gun you can shoot about a hundred times then it breaks? Also it pockmarks your land with acid pools - not beneficial in a lot of combat situations. Even in PvP you are going to have trouble getting one of those pools to spawn on someone else. The laser shotgun is also hilariously expensive. I don't plan on ever making a legitimate one with the recipe the way it is. Am I just a cheapskate or something? I want that redstone and iron for Industrialcraft, dangit! And even worse it can't even fire a full stack of ammo, and it isn't at all more devastating than a laser rifle (except I guess it makes a bit more fire per ammo, but ammo is free for this gun anyways...) It in fact does less damage (as stated in the wiki), but players and mobs can only get hit once every moment or so, so that multishot is going to be totally useless for everything except burning forests down, or maybe catching a few sheep on fire at once. Finally, the acid launcher is the other gun with a totally renewable ammo. But it is also very iron-expensive. Why would I spend ~7 iron on a gun that makes the environment super dangerous when I could use a laser rifle for free? or an industrialcraft mining laser for that matter! Please understand I'm not trying to tear your weapons down, I am merely calling out for a rebalancing of the ammo/weapon costs. Perhaps instead of losing your gun, it would just "break" and you could repair it at home in a plasmificator, with a smelt time slightly longer than a plasma. Perhaps you could always get caustic batteries back, and the % chance would be of getting a full one back (i.e. the gun doesn't waste a shot of ammo). Of course, you could keep it the way it is. But unless I see some sort of obvious advantage to the guns that cost diamonds and tons of iron, I am going to continue using the standard laser (because it only costs time!)"

There's a lot of neat options here. We could have breakable guns that can be recycled into new guns, or repaired to keep maintained. Either way, the mechanic of not having infinite guns when in the battlefield should be kept. I think ammo should be kept as renewable as possible, but perhaps have more strict stack limitations depending on the power of the ammo. Laser shotguns are very powerful for example, so maybe the pellets should only stack up to 8. The laser rifle is arguably the weakest rifle, so maybe that could have a full stack of ammo.

Perhaps a gun could be "filled" with ammo, as in using the durability of the gun. When it is empty it turns into an empty gun that must be reloaded, but has a chance of breaking as well. A broken gun would have to be repaired using some sort of tool or crafting recipe. I remember playing with a gun mod where you could repair the durability of a gun by crafting it with cotton (for cleaning of course).

Also, I feel the mod could use some more exciting stuff. Perhaps even some hooks into Buildcraft and Industrialcraft (but I'm no programmer, I am not going to judge the difficulty of undertaking such an event). What I would personally love to see is some custom mod-based weaponry, that gets unlocked based on what mods you have. For example, perhaps buildcraft could have an oil/fuel fuelled flamethrower. Industrialcraft could provide you with a reinforced iron/obsidium minigun, that fires iridium/uranium bullets. (you could hold down right click to continuous fire!) Or perhaps a rifle whose only difference to the laser rifle is that it does not make fire (so PvP is a little less vigorous, sometimes my friends just like to mess around but we are to lazy to repair the world).

I think Plasmacraft could easily become one of "those mods" that everyone needs to have. It's not too aggressive on the weaponry, they are not all generic guns. They all have unique purposes, and I think the coding that went into the projectiles is exceptional. There's more potential out there for sure, we just need to find out what it is.