I must have overlooked the button, but this message can be updated. Heres the last version:

Suppressing fire House Ruling

Meaning of signs
- = RAW
+ = Not explicitly stated in the RAW, but implicitly derived
* = House ruling
if rules are mixed they start in line with (-),(*) or (+)

Suppressing fire:
Conditions/consequences:
- must be in full auto burst
- weapon jams on 94 or higher. If the weapon is unreliable: on 91 or higher

Effected area
- The suppressing zone (SF zone) is short range and angle of 45 degrees
-* The kill-zone is (-)short (*)AND normal range and angle of 45 degrees

Suppresor:
- SF BS penalty is -20
+ all other modifiers applicable for the situation, aplly. E.g blinded, higher ground, size opponent, terrain, sight etc.
+* The only exceptions to these are (+)the short range bonus and (*)the prone target penalty
- If one or more (every 2DoS, upto max amount of the fire rate of the used weapon) hits are made, they are randomly spread over EVERYONE in the kill zone (cover or not). Cover is taken into account according to its rules.
* If one or more targets are prone, than the chances they're hit (in the random distribution) are halved. Example npcs a, b, c and d, a and b are in cover, c and d are prone then on a D6 roll: 1-2 =a; 3-4 =b; 5=c and 6=d. Everyone else shooting at the prone target get the standard -10BS
* if ALL targets are prone, the prone target penalty (-10 BS) applies.

Suppressee:
* As long as the SF lasts, everyone within the SF-zone must succeed a WP test at the beginning of each of his/her turn, or be pinned.
* The FIRST time you make this test during this combat you get a -20 penalty on your WP
+ If your 'pinned' you must succeed a WP test at the beginning of each of your turns, or your will still be pinned that round. If no one is shooting at you, meaning that you have to be at least outside of the kill-zone or the SF has stopped, you get a +30 bonus to your WP check. Once you succeed the check you are no longer pinned.
- close combat ignores pinning effect (auto success)

When pinned:
- you must either move to cover or out of SF zone (away from the suppressor)
+ any BS attack you make are at -20 penalty, all applicable modifiers for the situation apply, so you do get +10 BS if you're in short range
- while in cover you must remain in cover. You may move (only a half action) but only if you can remain in cover during your entire move
-pinnend charachters may only take half actions.
*if you are NOT in cover AND inside the kill zone then despite the 'half actions only rule' you may make a full action move. You may however not charge (anyone) or run. [optional: target must make agility test, +10 if half move, -10 if full move. In fail, target falls prone

It seems that I can't edit my original post so ill just stick the changes in the next post:
Updated are 'Suppressee' and 'When Pinned'

Suppressing fire House Ruling

Meaning of signs
- = RAW
+ = Not explicitly stated in the RAW, but implicitly derived
* = House ruling
if rules are mixed they start in line with (-),(*) or (+)

Suppressing fire:
Conditions/consequences:
- must be in full auto burst
- weapon jams on 94 or higher. If the weapon is unreliable: on 91 or higher

Effected area
- The suppressing zone (SF zone) is short range and angle of 45 degrees
-* The kill-zone is (-)short (*)AND normal range and angle of 45 degrees

Suppresor:
- SF BS penalty is -20
+ all other modifiers applicable for the situation, aplly. E.g blinded, higher ground, size opponent, terrain, sight etc.
+* The only exceptions to these are (+)the short range bonus and (*)the prone target penalty
- If one or more (every 2DoS, upto max amount of the fire rate of the used weapon) hits are made, they are randomly spread over EVERYONE in the kill zone (cover or not). Cover is taken into account according to its rules.
* If one or more targets are prone, than the chances they're hit (in the random distribution) are halved. Example npcs a, b, c and d, a and b are in cover, c and d are prone then on a D6 roll: 1-2 =a; 3-4 =b; 5=c and 6=d. Everyone else shooting at the prone target get the standard -10BS

Suppressee:
* As long as the SF lasts, everyone within the SF-zone must succeed a WP test at the beginning of each round, or be pinned.
* The FIRST time you make this test during this combat you get a -20 penalty on your WP
+ If your 'pinned' you must succeed a WP test at the beginning of each of your turns, or your will still be pinned that round. If no one is shooting at you, meaning that you have to be at least outside of the kill-zone or the SF has stopped, you get a +30 bonus to your WP check. Once you succeed the check you are no longer pinned.
- close combat ignores pinning effect (auto success)

When pinned:
- you must either move to cover or out of SF zone
+ any BS attack you make are at -20 penalty, all applicable modifiers for the situation apply, so you do get +10 BS if you're in short range
- while in cover you must remain in cover. You may move (only a half action) but only if you can remain in cover during your entire move
-pinnend charachters may only take half actions.
*if you are NOT in cover AND inside the kill zone then despite the 'half actions only rule' you may make a full action move. You may however not charge (anyone) or run.

and another update

Updated are 'Suppressor' and 'When Pinned'

Suppressing fire House Ruling

Meaning of signs
- = RAW
+ = Not explicitly stated in the RAW, but implicitly derived
* = House ruling
if rules are mixed they start in line with (-),(*) or (+)

Suppressing fire:
Conditions/consequences:
- must be in full auto burst
- weapon jams on 94 or higher. If the weapon is unreliable: on 91 or higher

Effected area
- The suppressing zone (SF zone) is short range and angle of 45 degrees
-* The kill-zone is (-)short (*)AND normal range and angle of 45 degrees

Suppresor:
- SF BS penalty is -20
+ all other modifiers applicable for the situation, aplly. E.g blinded, higher ground, size opponent, terrain, sight etc.
+* The only exceptions to these are (+)the short range bonus and (*)the prone target penalty
- If one or more (every 2DoS, upto max amount of the fire rate of the used weapon) hits are made, they are randomly spread over EVERYONE in the kill zone (cover or not). Cover is taken into account according to its rules.
* If one or more targets are prone, than the chances they're hit (in the random distribution) are halved. Example npcs a, b, c and d, a and b are in cover, c and d are prone then on a D6 roll: 1-2 =a; 3-4 =b; 5=c and 6=d. Everyone else shooting at the prone target get the standard -10BS
* if ALL targets are prone, the prone target penalty (-10 BS) applies.

Suppressee:
* As long as the SF lasts, everyone within the SF-zone must succeed a WP test at the beginning of each round, or be pinned.
* The FIRST time you make this test during this combat you get a -20 penalty on your WP
+ If your 'pinned' you must succeed a WP test at the beginning of each of your turns, or your will still be pinned that round. If no one is shooting at you, meaning that you have to be at least outside of the kill-zone or the SF has stopped, you get a +30 bonus to your WP check. Once you succeed the check you are no longer pinned.
- close combat ignores pinning effect (auto success)

When pinned:
- you must either move to cover or out of SF zone
+ any BS attack you make are at -20 penalty, all applicable modifiers for the situation apply, so you do get +10 BS if you're in short range
- while in cover you must remain in cover. You may move (only a half action) but only if you can remain in cover during your entire move
-pinnend charachters may only take half actions.
*if you are NOT in cover AND inside the kill zone then despite the 'half actions only rule' you may make a full action move. You may however not charge (anyone) or run. [optional: target must make agility test, +10 if half move, -10 if full move. In fail, target falls prone]

[deleted double post]

I figured I'd post this here, instead of finding some other suppressing fire thread...

I've made Pinning something that happens whenever someone is making a ranged attack at someone else. The Willpower roll is easier for single shots while semi auto and full auto bursts are, conversely, harder to withstand.

I never could understand why only when you're shooting (without really aiming) in a 45-degree arc at full auto, will the Pinning effect suddenly manifest. To me, being a the exclusive target of an autogun burst should be incentive enough to roll some Willpower checks and get behind cover really fast.

Modifiers to the Willpower roll to avoid Pinning:

Single shots: Easy (+20)
Semi auto burst: Ordinary (+0)
Full auto burst: Very Hard (-20)
Suppressive fire: Ordinary (+0)
Multiple attackers/high rates of fire: Difficulty increased by one or more steps.

These assume that the shooting is accurate enough to worry the target. The exact definition of "accurate enough" is left to the GM (me). The reason why Suppressive fire is less troublesome than full auto burst is that covering an area with the same amount of fire will result in less bullets landing near any one target - a tradeoff for the ability to pin a larger number of opponents at once.

your rule make (a lot of) sense, however don't you think this will impede the flow of the combat a lot?

There's that risk, but I'm hoping it won't I use random.org to get a bunch of 1-100 results fast, keeping the rolling to minimum. I also use GM fiat quite a bit, I just want to have some sort of guidelines written up so I'll have a baseline to work from.