Would I be right to assume if I'm wielding a bladed weapon and called shot vital area (eg arm), according to SR4 I get to add a +1 to +4 to DV and an equal amount of -modifiers to hit, do I get to sever the arm off?
I'm running on the assumption if the net damage exceeds target's body then it gets chopped off. Sort of like the knockdown effect. With the exception to called shot head melee attacks, that to slice target's head off you would have to do enough damage to outright kill the target.
So if I called shot the target's arm that is wielding a weapon and managed to slice that arm off, the target loses his weapon as well.

Am I playing this right?

I usually reserve that for Severe Wounds, particularly Heavy Damage... See Augmentation Pages 120-122 for more information...

Keep teh Faith

Thanks for clearing that up for me.

Sorry, I probably did not help that much, but the Sections I suggested reading would probably explain it much better than I could without actually pulling out a lot of those sections...

Keep the Faith

If it was me behind the BBS, I'd allow it with the called shot and a critical success.

What's a critical success?

Yeah, it looks like the exact rules are right there in the above page reference: 7 boxes of Physical and fail an Edge (1) Test could equal Limb Loss.

remind me to raise my edge, ouch.

Just always remember that what's good for the goose is good for the gander. If you start making called shots to lop off limbs, the GM has the rules memorized and can safely do the same.

Who's likely to feel the hurt for longer? The NPC that's probably about to die anyways, or the PC that's going to have to suck up some nuyen loss, some burnt essence, and some favors, in order to get a new arm?

My Sam in my last SR game lost his arm to damage.(Shoved a load of explosives down the throat of a queen inspect spirit, and she kind of bit it off) We were doing an early 50's campaign and we were not rich. It took me awhile to earn enough to replace the arm even with SR4s reduced costs which we used. But you know I thought it was awesome running around without an arm and using my off hand for like 4-5 runs before I earned enough to fix the situation.

If you take 7 boxes physical from one attack, you've already got big problems.

Like probably being knocked down.
BTW limb loss does not result in Essence loss. The implantation of 'ware reduces your Essence.

Critical Success is getting 4 or more hits above what you needed to succeed in the first place . .
so for example, if you need only one hit to succeed and you get 5 hits, then that's a critical success . .

Our rigger was "invited" to dinner by a Wendigo and ended up eating some rump roast. We all pitched in and bought him a cyber ass after the run was over......

I still say we need barrier ratings for bones, joints, muslce and tendons . . .
How much strength do i need with how many successes to rip the arm off of someone to beat them to death with?

You need to do 7+ boxes of physical damage with an unarmed attack, and then you're just using an Improvised Weapon.