Hello,

after thinking about it here is how I will manage Drain for overpowered casting :

Basic drain is by spell formula in S not P damage.

In addition the wizard need to sacrifice a number of square of his Physical monitor equal to the difference between the Spell Force/Power and his Magic Attribute. Thoses damage cannot be resisted nor avoided in any way as they are the life energy necessary to sustain the power surge above standard Magic Attribute.
If a mage Stun monitor overflow to his Physical monitor, the P damage can be deduced from the amount to sacrifice to sustain the spell.
The mage only loss conscience after the spell is launched and applied (last will energy).

Exemple :

Mage with Magic 4 cast a power 8 spell. Standard Drain is (F/2)+2S, in this case : (8/2)+2=6S. The mage also need to cross off 4 (8-4) square of his physical monitor. If the mage only have 2 square left on his stun monitor, and the drain is finally 4S,he sustain 2 square of damage overflow to his Physical Monitor, wich mean he only have to sacrifice 4-2=2 other square to sustain the spell.

Comment :

My own and personnal feeling is that it is closer to how Overpowering a Spell should behave. The nice thing is that the Drain is still on the Stun Condition Monitor wich means the Overpowering is not as much a freebee as when using the P monitor.

I prefer having Overcasting drain based on FOR instead of FOR/2.

Not according to the official SR4A rules.

I'd go for (Difference/2) P Monitors crossed off, but otherwise... I like it.

I just don't allow overcasting in my game. Why? Mostly because I usually only have 1, or at most 2, combats per session. If the mage nearly kills himself with drain during the one fight that session, it doesn't matter a lot.

So you have a problem with the Mage allmost dying from Drain, not overcasting itself? Let him die. Two characters later he either has learned his lesson and stops overcasting like a tool, or he will keep losing characters to it.

Yes, that was my proposed house rule
I've edited for clarity

That's a bit too close to blood magic, just using Stun instead of Physical damage.

Yes it is... and it should be.

Overcasting is nothing more than Life Magic, the good guy aspect of the Blood/Sacrifice Magic. At least in my perception.

No. I'm just saying that its not going to significantly impact things if he gets severely wounded by overcasting. example: he overcasts a force 8 stunball at a group of enemies, making a hard fight into an easy fight. They win. There's no more combat that session. It really doesn't matter if he's got 5P damage or not. There's some roleplaying left to do, but his raging headache isn't likely to make them fail at that. Since the overcasting isn't really a threat to him, I don't let him do it at all.

Wow... are we just ignoring the -1 penalty to all die rolls that come with have 5P? I don't know about you, but a one die penalty has forced my characters into some fairly hairy situations. Lessee... I have a 4 CHA, but no Negotiation or Intimidation skill. Just after the fight we have a survivor that we want to question. No skill means I have a dice pool of 3. Now we take that penalty into account and now I have 2 dice total. Odds are I won't even get one success.

This happens all the time until the 'runner gets fairly experienced and has the karma to better round him/herself out. Heck, during my last 'run, playing a mage with 20 karma total, I was injured with 5 boxes of damage from drain (healing other members of the party... and yes, I overcasted so that they could have most of their health boxes available to them) and we were trying to make a getaway with baddies chasing us. Most of us are on bikes. Mine had a Pilot rating of 1, Handling +1, and Motorcycle Gyro Stabilization. My REA was a 3, and I currently have no pilot skill (it'll be the first thing I pick up after this 'run, let me tell you!). So, I went with defaulting to my meat (since it was better than the bike's Pilot rating--I figured I'd trust myself over a machine). REA 3, -1 for defaulting, +1 for the bike's Handling, -1 for Health penalties for a total of 2 dice. Traffic was moderate so the GM ruled all Pilot tests had a threshhold of 3. I throw in Edge (3) and roll 2 success (about average on that dice pool). I immediately have to make a crash test (thanks to gyro stabilization I have +2 dice for that test). 4 dice for the crash test and I get 2 successes. Down I go! Oh yeah... I was seriously wanting for that lost die due to Health penalties!

Life magic is just blood magic that comes from yourself rather than a third party.

The team has a face. And a rigger, with a van. Yeah, the drain could still adversly effect some part of the rest of the session, but it's not going to kill him.

Sounds like to me like you have the perfect set up for a desperate battle. Just have the players fight one battle like they use to, and have them overcast or whatever they like. Then, when they think they are heading back to safty have them attacked again. With the spellcaster heavily wounded they probably don't have anything to deal with a spirit or another magican do they? I'm not sugesting this as a way to kill the players. In a worst case senario you could just fumble the dice to let them survive. The important thing is that they should go "woah! That was close. Maby we shouldn't be so reckless next time". You don't have to do this every time either. As long as you keep them guessing, they are never sure wether or not they should waste everything in combat or not.

Since you say that you only have one fight per session leads me to belive that you let the PCs rest between the sessions. When I GM it doesn't work like that. I give the players a mission, and if they can't finish it in one session we pick up where we left of.(Usually never takes us more than two sessions though)