The way I see it broken down, most weapon types are represented by existing 2010 weapon and supernatural rules, with only a very few modifiers needed to represent them in-game (and at least attempt to balance it out).To do this, I've made a way to give weapons attachments and make combination weapons like gunblades, and a few modifiers to give weapons that extra spicy bit of flavor that can make games interesting, with quick and simple rules.
Rifles on the battlefield often attach anything from flashlights to bayonets, grenade launchers, and even underslung flamethrowers and shotguns to the ends of their barrels. As if Xzibit himself were there to put a machinegun on your machinegun (so you can run out of ammo while you run out of ammo, dawg), so too can you make swords with rifles in them behave under the brikwars stats.
Any combination weapon should cost as much as it would for both weapons, and one must specifically be designated the Primary weapon and it's Attachment. Primary weapons with attachments behave no differently (although are more prone to breaking from critical failures) than without, but the attached weapon will always be a size 1" version of whatever ranged weapon it is based off of, as well as requiring a full turn to reload (and ammunition for explosives!). Melee attachments may not be used to parry, and may be no larger than the weapon they are attached to; in other words, the primary weapon must always be the larger one. The melee attack's use and damage ratings are determined by measuring the entire weapon, and treating it as a melee weapon of that size, including angry inch attacks and movement penalties. A knife on the end of a rifle may be a hand weapon normally, but when attached to the end of a big enough rifle it can rival the reach of even the longest pole-arms!
-Killzone's Original Helghast Assault Rifle uses an Autogun as it's primary weapon, and an undermounted shotgun as it's attachment.
-A double-bladed energy-sword is a heavy melee weapon as a primary, but with a second blade attached at the end, it may also be treated as if it were a 2-handed weapon. It may only parry with the smaller end, however.
-A gunblade consist of a heavy weapon or hand weapon as the primary (depending on size), with a pistol built into the weapon.
-A rifle with a wrench or other tool on the end of it may use the tool as if it were an attachment with an action. Talk about masculine!
-Be creative. Flamethrowers on your launchers, slingshots embedded into your assault rifles, whatever. If you can build it, you can stat it!
Double-barreled Shotguns behave as shotguns of the appropriate size, but may fire twice. May be fired one at a time or both in one turn, but the whole weapon must be reloaded after both shots are fired.
Scopes add +1d6" to the range of a weapon, but only while stationary and aiming. This value must be re-determined at the beginning of a minifig's turn if they continue to look through their scope, and they may only do so in one direction. Technically, Binoculars function as a scope for all line-of-sight style bonuses, but they cannot be used while attempting to aim any kind of weapon.
Silenced weapons are totally silent, and have half range. Remember that attacks out of range are +1UR and -1 Damage for every inch out of range: you'll be doing it a lot. Only a hit will reveal the location of the assailant, and missed shots will keep all cover bonuses to stealth the user may have. However upon rolling a critical failure, the minifig loudly shouts "Damn, I missed!"
Carbines cover SMGs as well as rifles, and are simply treated as having the range of a size 1 weapon, but the damage, use rating, and handedness of the bastard version of a weapon. While stationary, they may be tucked under one arm and used with a shield.
Big-Ass weapons are the whole category of weapons that are "it's like this kind of gun/sword, but bigger." Most of this type of thought should be discouraged in favor of easier to remember stats, but should someone remain stubborn, or have largely outnumbered feces and a license for better arms, then go ahead and let them. Big-ass weapons have +1 to UR and +1 to damage. Though impractical, one may add +2 to each for bigger-ass guns and max out at +3, the biggest-ass weapons.
Cursed weapons and armor, once donned, can never be removed voluntarily until death. In addition, they deal 1d4 damage immediately upon pickup (subsiding once a 1 is rolled). Units starting with cursed weapons are assumed to have already shrugged this damage off. This 1d4 curse bonus damage is also applied towards every enemy who is successfully hit by the weapon. A cursed flamethrower may or may not be entirely broken.
Needler Just because I got one in the brikarms pack, we figured the needler's just a short-range weapon with a twist: when a critical is rolled for skill, there is a 1d10 explosion at the end of the target's next turn. Place a marker to keep track of this.
Warming up Some weapons, like the halo plasma pistol and most miniguns, take a full turn to warm up. This can be represented by overcharging the battery, spinning up the barrels, drawing dark energy from the ambient battle's lost souls, or whatever seems appropriate for the weapon. Regardless, it will cost one action. By doing so, they may add +1d6 damage.
Missile Lock means that a minifig with homing rockets (or bullets in hard enough sci-fi) can make their skill roll twice and take the better roll if they stop to aim, saving valuable rocket ammo for those especially hard to hit large rockets. In other words, treat the weapon as if it had a blessing. If a minifig is piloting a vehicle that can arguably dodge the missile, they may attempt to use their stunt roll as if it were a parry. If successful, the missile is dodged, and if successful enough to make the weapon's use, the pilot may even pick the target through evasive maneuvering.
Monopods, bipods and turrets are surprisingly already covered in the rulebook, allowing gunners and minifigs to carry around and use size 2 weapons! Keep in mind that large sniper rifles requiring bipods can count as size 2 guns, and heavy machineguns as autoguns. Setting up takes a full turn, and carrying the weapon costs half of a minifig's move speed.
Some turrets can also be littered around the battlefield that are completely stationary, but can be mounted upon.
For some games, the type of projectile being fired from a weapon might actually make a difference. For the most part, you can add a supernatural die to a weapon to add damage, range, or whatever effects different ammo might have. Some weapons can also switch their ammo types (like loading armor piercing rounds into a sniper rifle, for example), but they require an action to do so, and that the minifig be carrying around the new ammo type (non-civilian minifigs are assumed to always be carrying standard bullets). Again, be creative, but here's what I've been running with:
Incindeary weapon: 1d4 SN, applicable to damage only
Armor Piercing: 1d6 SN or 1d12 SN, applicable to damage only
Plasma: 1d10 SN, appliable to damage or range
Laser: 1d6 SN, applicable to damage or range