So I was looking at the reduced weight weapon mod from arsenal, and saw that it says that "Material strength has not been changed, but in cases where the weapon’s weight may be important, such as when throwing it, generally assume it has been cut in half."

What effect does that really have? I mean, does it double the ranges? reduce the damage? what good is this mod?

Due to the abstraction of SR4, & the removal of equipment weight listings, this modification, mechanically, does nothing. It is purely flavor. It may, however, assist you in convincing your GM to let you carry around a trio of Panther Cannons.

In light of the total lack of guidelines for limiting throwing range on weight, the issue will probably will never come with standard ranged combat. However, the spells Fling and Levitate do have limits based on the mass you can manipulate with them, so the weight (once arrived-at, anyway) would matter. With Fling, for instance, you could make a thrown weapon attack with an up to 1 kg object with just a Force 1 casting - which would cover most actual throwing weapons handily... or, say, a reduced-weight sword or axe for more damage.

soo... other than the light, subtle hints of flavoring it grants, this is completely useless?

isn't that just mopeworthy and a half...

S'what you get when you convert to a rules-light and overly-abstract system but still try to cut-and-paste rules from previous editions.

Mechanically it grants no advantage. If Shadowrun were a wargame it'd have no point.
As a roleplaying game some folks may want to have a weapon that weighs less than normal.

Which they should be able to handle in exactly the way they handle fluff mods on armor (such as color shifting fabrics or temperature controls). This mod literally takes up 1/6th of your modification capacity. There should be some benefit to it if it's going to cost you another game mechanic in return.

I agree with Dr. on this one - without a mechanical benefit, it should not have a mechanical downside - aka using up capacity.

My sniper has in on his extended barrel rife so i can lug that thing where needed I has mechanical purpose skin pocked can only carry 1KG thus you could use it to fit more in you pocket. But its pure mecanical value is not clear.

Cracker Jack just had his tricked-out AK-97 run out of ammo on him, and he's the only person in position to shoot the Maguffin to prevent the {Random Corporation} from getting it (What they're paid to do.). h@><><0R is the only other 'Runner in position to throw Cracker his weapon, a Ares Predator IV. Unfortunetly, like most Old Skool Decker/Hackers, he's out of shape.

With a standard Ares Predator IV, it's a extreme distance throw at h@><><0R's Strength. With his current skill, that takes it out of his ability to have any dice, and he used up all his Edge earlier on the Hackfest against some nasty IC.

With a Light Weight Ares Predator IV, it's still long distance, but the difficulty is halved, and h@><><0R's got a SHOT at doing it, even without Edge.

In addition, h@><><0R does not like the "Baggy Pants" look of the Orxploitation Rappers, and didn't like the way the heavy pistol dragged his pants down. So he got the light weight mod.

There, an in-game reason.

You want another one?

Grenades.

Rocket Launchers and Missiles.

The Davy Crockett.

Anti-Material Sniper Rifles that are used by Asian Elven Sailor Fuku-Wearing Schoolgirl Shadowrunners.

In 3rd Ed. where we do worry about loads, it does make a difference. (Join the resistance, play 3rd ed!)

In SF or Raygun could probably talk about this better. I know in RL she has a revolver with lighter weight materials and complains about it.

CanRay - weight has nothing to do with throwing distances, at all. So no, that is not an in-game reason.

"...but in cases where the weapon’s weight may be important, such as when throwing it, generally assume it has been cut in half."

I'm not saying he can throw it any FARTHER, but it's easier to throw due to the lesser weight.

Of course, lesser weight, easier to manipulate. Strong wind, and here comes that grenade again. Oh, look, an Air Elemental.

Once again - that is pure fluff. There are no weight listings in the game, & weight has nothing to do with how far or easy it is to throw it.

Half of nothing is still nothing.

for 3rd ed, weight matters. a lighter gun is easier to tote but because of it we throw off accuracy. In RL I have a S&W .38sp with an extended j-frame (so it's hammerless) and lighter alloy. It is light and sits easily in a jacket pocket without too much bulk. BUT the trade off is the damn thing has so little mass it kicks like crazy-nothing absorbs the shock and it throws ALL the force of the bullet back into my hand. Just firing through a box (50 shots) for the damn thing can make my hand ache for a day in a way the .357 with all the mass to make it heavy, never does.