[Magnaric]

So, in a SR4 game and playing an ex-black ops Troll weapons/assault/wetwork specialist. Story goes he "liberated" an early prototype Onotari Arms Manhunter(years before the regular version came out) from a SK facility. Anyways, posting the stats below to see if my math is correct. I posted the mod slots or spots taken in brackets.

Onotari Arms Manhunter(Troll-sized at start)
 +Advanced Safety (1)
 +Internal Mark 74 SmartLink
 +High-Power Chambering (2)
 +Improved Rangefinder (1)
 +Sound Suppressor (Barrel)
 +Easy Breakdown, Manual (1)
 +Bayonet Mount (1)
 +Imaging Scope, with Image Magnification and Ultrasound (Top)
 +Shock Pad (Stock)
 +Sling (Doesn't take a spot)
Underbarrel Weapon
GL-67 Grenade Launcher (Comes with AirBurst System built-in)
 +Advanced Safety (1)
 +Internal Mark 74 SmartLink
 +Electronic Firing w/ Trigger Removal (2)
 +Bipod (uncertain if can use grenade launcher with this)

As far as I can tell, it normally does 9P -3AP, has -3 to detect shots(Suppressor), RC of +3(sling) or +4(bipod). ALso, here's a pic to represent it.

[Mantis]

Unless your GM allows overmodification, you have spent too many slots. An under barrel weapon takes up 3 mod slots.

[Magnaric]

Yes, but can you not then modify the underbarrel weapon with appropriate changes? Or is an underbarrel weapon considered as stock and basically un-modifiable?

[RHat]

Underbarrel weapons, if I recall correctly, are limited to 3 mod slots.

[Mäx]

Underbarrel weapon can't be bigger then the one you attaching it to, assuming that the Manhunter is an assault rifle, i would say GL-67 really doesn't qualify.

[Magnaric]

The grenade launcher is a little hefty, thought most of its extra bulk is the stock and firing mechanism, which I could get rid of in liey of the main rifle's ones, whereas the Manhunter is a battle-rifle, which is something between an assault rifle and a sniper rifle(as well as Troll-sized). But you are likely right about the mod slots, in which case I'd just have to remove the bipod and possibly design it as being a stationary attachment.

[Mäx]

Sorry but GL-67 is in most ways bigger then battle rifles.
Seriously where talking about 20 round capacity drum fed grenade launcher.

[Magnaric]

Probably right, I relooked at it and it's kind of large. I can likely change that to use a smaller launcher though, and the only difference will be ammo capacity and what addons it has. Good call on that. 

[RHat]

There is a pistol sized one in Arsenal.

[Magnaric]

Yeah, noticed that, might swap it out for that one. Been conferring with some other people too, going to have a few changes to run past my GM before this next session. All excellent tips though, appreciate it.

[SpatulaODoom]

How is it your sling is providing 3 points of recoil compensation? My understanding is it provides 1 point, with the shock pad providing a 2nd point. Which is immediately sucked up by high powered chambering's automatic 2 points of recoil.

Underbarrel weapons do not receive any recoil compensation from the primary weapon's mods/accessories, nor does anything on the underbarrel weapon provide any recoil comp to the primary weapons.

In addition, Underbarrel weapons are limited in what sort of recoil they can benefit from. Gas vent, heavy barrel and electronic firing only (No bipod sorry).

Oh and underbarrel weapons have their ammunition halved.

EDIT: I don't have the book that the battle rifle is from (I'm assuming one of the gun heaven books), but here's my suggestion.
Onotari Arms Manhunter(Troll-sized at start)
 +Gas vent 3 (2)
 +Internal Mark 74 SmartLink (I'm assuming this is built in)
 +Improved Rangefinder (1)
 +Sound Suppressor (Barrel)
 +Imaging Scope, with Image Magnification and Ultrasound (Top)
 +Shock Pad (Stock)
 +Sling (Doesn't take a spot)
 +Underbarrel Weapon (3)
ArmTech MGL-12
 +Internal Mark 74 SmartLink (1)
 +Airburst link
 +Electronic Firing w/ Trigger Removal (2)

You're better off with gas vent 3 + Ex-Ex ammo than with High Powered Chambering by a long shot. If you run into spirits or heavy armor then bust out the high explosive minigrenades. Drop the improved rangefinder, battle/sporting rifles have a 100M short range alone. Beyond that you have an imaging scope, use it. If you really want the advanced safety (it's sorta worth it on the conceptual level) drop the gas vent down to 2 to free up an extra mod slot in the main gun and drop the trigger removal from your grenade launcher. I figure a 6 shot version of the MGL-12 should be small enough to pass muster since these aren't 40mm grenades we're talking about.

[All4BigGuns]

How is it your sling is providing 3 points of recoil compensation? My understanding is it provides 1 point, with the shock pad providing a 2nd point. Which is immediately sucked up by high powered chambering's automatic 2 points of recoil.

High power chambering penalty may be "fluffed" as recoil, but it is just a penalty. RC doesn't count for that one as far as I know.

[SpatulaODoom]

I'm trying to find a nice way to say "that's retarded" without saying that's retarded.
If that's how it's "fluffed" then where is the crunch? It's in the same sentence. It's a dice pool penalty due to recoil. It's recoil.

[Magnaric]

Sorry, I may have p[harsed that wrong. The RC of 3 was from the sling AND the shock pad, for a total of 3, not individually.

And yeah, I actually altered things a little after conferring here and with some other people. Kept the High Power Chambering but lost the Sound Suppressor and Improved Rangefinder, and replaced it with Gas Vent 3 instead. That effectively does away with my mod point overrun, and kept the damage output. Loses something on Subtlety, but this weapon was never exactly the sneaky type anyways.

I do realize that there are mechanical "flaws", but it actually fits with this weapon being designed as a stand-alone prototype rather than an optimized final version, which plays into the whole character backstory and such. But massive help on suggestions all around, thanks guys.

Oh, and as I read it, have to agree with SpatulaOfDoom, the High Power Chambering adds +2 to total recoil, which then should be able tyo be overcome by Recoil Compensation. Essentially it's just because you are firing a larger caliber round with more force behind it, so that force is getting sent back at you, hence recoil.