Breaching vs. Cutting, Arsenal Explosives question Options

[TheOneRonin]

Greetings all. I've been familiarizing myself with the advanced explosive rules in Arsenal, and I've run into an issue. First off, let me quote a few relevant pieces of text:

Cutting requires far less explosives than breaching, but more preparation time.

Makes sense, but I can't get it to work out in practice.

Okay, lets say we are faced with a security door. That counts as Reinforced Material, so we have Structure Rating of 9, and an Armor Rating of 8.

Let's also say that we have a drone carrying 200 foam explosive canisters, each packed with 1 kilogram of Rating 4 foam explosive.


So if we decide to breach the door, lets figure out how much explosive it's going to take.

Arsenal gives us the following:

DV required = (Radius[m] x Structure Rating) + (Armor Rating ÷ 4)
Explosive weight = (DV ÷ DV Multiplier ÷ Explosives Rating)squared in kg

So to blow a 1 meter diameter hole, we need a DV of
(.5 * 9) + (8 / 4)
(4.5) + (2)
6.5 or 7 DV

Let's say we are just putting the explosives on the ground, so the Multiplier is x1.

The weight in kilograms is:
(7 / 1 / 4) squared kilograms
3 kilograms

So 3 kilos of rating 4 foam explosive will put a 1 meter diameter hole in our security door.

Good 'nuff.


So let's say instead of breaching it, we decide to try cutting it.

We are going to attempt to cut a 1 square meter hole out of the door.

We are still using rating 4 foam explosive, and we will shape it into four 1-meter lines.

The DV formula for cutting is: (sqrt of kilos/meter)*(Rating of explosives)
We also get 1 additional AP per net hit made on the demo extended test (assume no net hits, so no AP)

The door can buy 2 hits from it's armor, effectively giving it 11 damage boxes.

If we want to do 11 boxes of damage, we will need almost 9 KILOGRAMS PER ONE METER LINE!!!
DV = (sqrt 9)*(4)
DV = (3)*(4)
DV = 12

Holy shit. You need a grand total of 36 kilograms of the same explosive to cut a 1meter square hole out of that security door, whereas you only need 3 kilos to blow a 1meter diameter hole. WTF???

Please tell me my math is wrong...

[edit]
My math WAS wrong, so I fixed it. But all the correction did was change the required mass of the breaching charge from 5 kilos to 3, exacerbating the problem with the cutting charge calculation.
[/edit]

[hyzmarca]

You half a target's armor when the explosive is attached directly to is (SR4 p. 315) and why the hell do you have 0 net hits? If you're going to do it keep making the extended test until you have so many hits that it doesn't matter anymore. Also remember that Each net hit adds to the explosive's DV.

[TheOneRonin]

You half a target's armor when the explosive is attached directly to is (SR4 p. 315) and why the hell do you have 0 net hits? If you're going to do it keep making the extended test until you have so many hits that it doesn't matter anymore. Also remember that Each net hit adds to the explosive's DV.

A couple of things. First, the demo rules in Arsenal supersede the demo rules in the BBB. In Arsenal, net hits on the "Cutting" explosives test only add to the AP rating of the explosive. Secondly, even if you get enough hits to ignore all the targets armor in the above case, you STILL need each meter-long strip of explosives to do 9DV to cut through the Reinforced Material (Structure Rating 9). According to Arsenal, the DV for a cutting attempt is computed as follows:

DV = (sqrt of kilos/meter)*(Rating of explosives)

So for the above door, even if you generate enough successes to ignore the armor entirely, you either need a single kilo of rating 9 foam explosive, 4 kilos of rating 5, or 9 kilos of rating 4 PER LINEAR METER.

Like I said, either my math is wrong, or something is very wonky with the advanced demo rules in Arsenal.

[hyzmarca]

A couple of things. First, the demo rules in Arsenal supersede the demo rules in the BBB. In Arsenal, net hits on the "Cutting" explosives test only add to the AP rating of the explosive. Secondly, even if you get enough hits to ignore all the targets armor in the above case, you STILL need each meter-long strip of explosives to do 9DV to cut through the Reinforced Material (Structure Rating 9). According to Arsenal, the DV for a cutting attempt is computed as follows:

DV = (sqrt of kilos/meter)*(Rating of explosives)

So for the above door, even if you generate enough successes to ignore the armor entirely, you either need a single kilo of rating 9 foam explosive, 4 kilos of rating 5, or 9 kilos of rating 4 PER LINEAR METER.

Like I said, either my math is wrong, or something is very wonky with the advanced demo rules in Arsenal.

The demolition rules in Arsenal don't supersede the original rules; they add to the original rules.

[WearzManySkins]

I agree with hyzmarca, the Arsenal explosive rules enhance or add to the ones in the BBB.

WMS

[TheOneRonin]

The demolition rules in Arsenal don't supersede the original rules; they add to the original rules.

When it comes to breaching, they change the way damage to a barrier is calculated.

To determine the size of the hole made by an explosive, start
by figuring out its DV. If the explosive is up against a structure,
it will actually have two DVs: one is calculated as outlined on p.
315, SR4, and is used as the blast against characters, vehicles, and
anything else that happens to be inside the blast radius. The other
DV is calculated as explained below, and is used to figure out the
effects of the explosion on the structure being blown up.

This second DV is equal to the square root of the number of
kilograms of explosives used, times the rating of those explosives,
and also multiplied by the appropriate factor from the Charge
Positioning Table. Note that no skill test is required here (be-
yond the one for Handling Detonators, p. 88)—anyone can jab a
detonator into a block of C4 and stick that block against a wall.
Demolitions skill applies only if the character wants to actually
work out how the quantity of explosives needed, as explained
under Calculating the Charge Needed, p. 92.

So the mechanic of the skill test net hits added to DV don't really apply. Or, at least, don't apply when determining how much damage the explosives actually do to the structure you are trying to breach.

With the advanced rules, the GM rolls the skill test, with modifiers based on how much intel the demolitionist has about what he is trying to breach. The results determine the quantity of explosive that the demo guy THINKS he/she needs to do the job properly. The actual value may be more or less, depending upon the number of hits scored.

With Cutting Charges, the rules change yet again:

PLACING CUTTING CHARGES
A cutting charge needs to be properly placed for it to work to
full effect. The character setting the charge rolls a Demolitions +
Logic (5 minutes) Extended Test, with a threshold equal to twice
the number of meters to be cut, rounded up (for beams, pillars,
etc. use the circumference as the distance to be cut). For example,
cutting through a steel prison bar that is 3 centimeters in circumference
would require only one hit (3 centimeters = 0.03 meters,
so it would need 0.06 hits, which rounds up to 1), but cutting a
one-meter square hole in the side of a ship needs 8 hits: a one meter
square has four sides of 1 meter each, making 4 meters in
all, and 4 x 2 = 8.

EFFECT OF CUTTING CHARGES
The DV of a cutting charge is calculated by taking the square
root of the number of kilograms of explosive per meter of cutting
charge, multiplied by the rating of those explosives. The charge
has an AP equal to the number of net hits rolled on the Extended
Test, plus the AP of the explosives used in the construction of the
charge. (Normal explosives have an AP of 0, but certain types,
designed for use in cutting charges, have higher AP ratings—see
Explosives, p. 85.)
When the charge is set off , the barrier uses its Armor rating
against the charge’s DV as normal; as with breaching charges, it is
recommended the gamemaster buys hits instead of actually rolling
the Armor rating’s dice. If the remaining DV equals or exceeds
the Structure rating, the barrier is cut along the entire length and
shape of the cutting charge. No other hole is made in the barrier
unless the character is using what the gamemaster considers an
excessive amount of explosives (in that case, use the rules for
breaching charges to determine the eff ect on the barrier, even if
the character set them as a cutting charge).

Again, there doesn't seem to room in these rules to allow for "net hits add to DV" or "use 1/2 armor if explosives are placed against a structure".

[hyzmarca]

Again, there doesn't seem to room in these rules to allow for "net hits add to DV" or "use 1/2 armor if explosives are placed against a structure".

It doesn't say you don't and if it doesn't say you don't then you do.

[TheOneRonin]

It doesn't say you don't and if it doesn't say you don't then you do.

Indeed. Can you give me an example of how the Cutting rules work with the explosive rules from the BBB?

[hyzmarca]

Its simple. For cutting when the explosive is placed directly on the surface total DV = [ √((mass in kilograms)/distance in meters)]*(Rating)] + (Net Hits) and AP = [(-half) + (net hits)]

This, with say 4 net hits a the explosives expert totally negates the door's armor and is able to cut it with only one kilogram of rating 5 per meter or (5/4)^2 of rating 4 per meter.

Now, to create a circular hole 1 meter in diameter you only need a curve line π meters in length of the actual requirement is (25/16)π kilograms for rating 4 foam. This is slightly more than the breaching change but can be further reduced by spending time to get more net hits.

With 5 nets hits you only need π kilograms of rating 4 to cut the hole and with 6 net hits you only need (9/16)π kilograms of rating 4 to cut he hole.

[Muspellsheimr]

The demolition rules in Arsenal don't supersede the original rules; they add to the original rules.

Demolitions is the act of destroying something - in Shadowrun, this means using the Demolitions skill (p. 123, SR4) to set explosives for maximum effect. The rules in this section replace those listed under Explosives, p. 315, SR4.

It does not say in the Cutting section that Net Hits add to the DV, and thus they do not. It is false unless stated otherwise, not vice-versa.

[hyzmarca]

It does not say in the Cutting section that Net Hits add to the DV, and thus they do not. It is false unless stated otherwise, not vice-versa.

I reject your reality and substitute my own!





Cutting is better for making holes of less than a a decimeter. I think. The problem is that when making calculations for a circular cut of a decimeter in diameter the explosives DV is the square root of a variable times the product of two irrational numbers divided by the square root of a transcendental number. Breaching is still better at 1 decimeter (29/40 kilos vs 81π/160) but cutting is better at 1 centimeter is diameter (209/400 kilos vs 81π/1600 kilos). Yeah, without extra DV cutting sucks.

[TheOneRonin]

Yeah, that's sorta what I was trying to get at. In my mind, it should take less explosive to cut a 1 square meter hole in a given material than it does to just breach a 1 meter diameter hole. However, it should take a lot more time to setup the cutting charges, since all breaching takes is slapping the explosive on the surface and pressing the "detonate" button on your commlink.

It would make sense that way, and I even believe that is how the devs intended it to work, but the mechanics just don't deliver that.

And I should point out that even if you use the following explosive rules from the BBB, breaching is STILL more efficient than cutting, which doesn't really make sense.

1. Hits on demo test add to effective rating of explosives
2. DV is doubled vs. barriers
3. Barrier rolls armor (instead of double armor) to resist when explosives placed on the surface of the barrier.

If those rules apply to cutting, they apply to breaching too.


One possible fix is to have the net hits on the Cutting Demo test either add directly to DV, or to function as a multiplier to DV. That would make cutting a much more efficient option when you have the time to do it.

[The Jopp]

Is it just me or is the entire amount of explosives needed in SR4 completely wonky?

Considering how powerful explosives are today not much difference should be made in 60 years.

I mean, really, would it really require KILOGRAMS of explosives to make a hole in a wall or could it be 1/10 of kilograms used. Instead of using kilograms you split the amount by 10.

Or is it that the explosives rating goes from firecracker strength at rating 1-2 and commercial at 3-4 and above that you get into special equipment strength and military applications.

I just find the amount of explosives needed a bit excessive.

[Magus]

Can you imagine the death and destruction you could cause with a simple fireworks display gone wrong? I mean those are some huge rockets and mortar balls that pack a lot of BOOM!

[TheOneRonin]

Is it just me or is the entire amount of explosives needed in SR4 completely wonky?

Considering how powerful explosives are today not much difference should be made in 60 years.

I mean, really, would it really require KILOGRAMS of explosives to make a hole in a wall or could it be 1/10 of kilograms used. Instead of using kilograms you split the amount by 10.

Or is it that the explosives rating goes from firecracker strength at rating 1-2 and commercial at 3-4 and above that you get into special equipment strength and military applications.

I just find the amount of explosives needed a bit excessive.

I've been spending time talking to a guy I work with who used to be an Engineer Sergeant in the 19th Special Forces Group. According to him, you DO need a metric shit-ton of explosives to breach walls if the charges aren't tamped. That's probably why the explosives rules in Arsenal give DV multipliers for properly tamped demo charges. Of course, the better your setup, the smaller quantity of explosives you need to do the job effectively.

When I was playing with the numbers, I found that commercially available explosives (rating 3) are extremely powerful, especially if you are using them to breach something that is underwater, or if you are able to properly tamp them.

[hyzmarca]

One issue is that, in real life, explosives obey the inverse-square law for heat and the inverse-cube law for shockwaves, meaning that power drops exponentially with distance. In SR, power drop linearly with distance.

[Tunnel Rat]

I can only hope that the rules for cutting with explosives have left something out.

The problem is that they aren't boosting the power of the explosives when you're 'cutting'. So, you need to do more DV, which requires that you use far more explosives because the ratio of DV to kilogram is a squared value.

Just use this to calculate the amount of explosives while cutting:

DV required = (Barrier Thickness[m] x Structure Rating) + (Armor Rating ÷ 4)
Explosive weight = (DV ÷ DV Multiplier ÷ Explosives Rating)squared in kg (per 1 meter)

So, if I assume that our SR 9, AR 8 door is 10 cm (.1 m) thick then:

(.1 x 9) + (8 ÷ 4) = 2.9 or 3 DV.
Thus, Explosive weight = (3 ÷ 1 ÷ 4)squared = 0.5625 kg of explosives per meter. So, given a square with 1 meter sides, that would be 2.25 kg of explosives in total. That's better than 3 kg for a 1 meter circular hole.

If you want to compare them accurately, to cut a 1 meter diameter hole in the door would take Pi * 0.5625 kg or 1.77 kg of explosives. So, you'd use a little over half of the amount of explosives to cut via this method.

[TheOneRonin]

I can only hope that the rules for cutting with explosives have left something out.

The problem is that they aren't boosting the power of the explosives when you're 'cutting'. So, you need to do more DV, which requires that you use far more explosives because the ratio of DV to kilogram is a squared value.

Just use this to calculate the amount of explosives while cutting:

DV required = (Barrier Thickness[m] x Structure Rating) + (Armor Rating ÷ 4)
Explosive weight = (DV ÷ DV Multiplier ÷ Explosives Rating)squared in kg (per 1 meter)

So, if I assume that our SR 9, AR 8 door is 10 cm (.1 m) thick then:

(.1 x 9) + (8 ÷ 4) = 2.9 or 3 DV.
Thus, Explosive weight = (3 ÷ 1 ÷ 4)squared = 0.5625 kg of explosives per meter. So, given a square with 1 meter sides, that would be 2.25 kg of explosives in total. That's better than 3 kg for a 1 meter circular hole.

If you want to compare them accurately, to cut a 1 meter diameter hole in the door would take Pi * 0.5625 kg or 1.77 kg of explosives. So, you'd use a little over half of the amount of explosives to cut via this method.

I suppose that could work. Still, I'd like to see some official word on how it's supposed to work. Especially since I'm about to be a former SBS Underwater Demo expert in an upcoming game.

[TheOneRonin]

So that's it? No one else has any more info about the explosives rules in Arsenal?

Has anyone used them, or any GMs had a player use them in their games?

[Method]

OneRonin: I reread the rules for breaching/cutting and I think you're right- there is something a little off about the amount of standard explosives.

Have you done the calculations using the linear cutting charges? Maybe the rules were written with those in mind, though it seems odd that cutting charges are always considered untamped. When you read the description of the cutting charges it sound like they have built in tamping (the angled iron that "focuses the explosive blast onto the line to be cut"). Anyway that -5 AP will make some difference, but not enough to correct the massive amounts of explosives you need for cutting. Doesn't make much sense.

One thing I noticed was the note about rubble obscuring up to half of the hole you create with breaching. It gives the impression that breaching is a really messy affair, but cutting has no such rule. Maybe that is one distinct advantage to cutting but I don't know if thats worth the extra explosives either.

As far as the rules in Arsenal superseding the rules in the BBB- my interpretation was that the multiplier from the Positioning Table on page 90 basically replaces the "DV x 2 against barriers" from the BBB. In other words the BBB assumes that all charges are placed "Higher above ground than hole radius, untamped" (x2) for the sake of simplicity.

[Tunnel Rat]

Even if you switch to the cutting charges, the problem remains. Let's suppose that you've managed to get 3 successes on the demo extended test and have gained -8 AP. You would now need a DV of 9 instead of a DV of 11.

So:

DV = sqr(kg) x r
OR
9 = sqr(k) x 4
k = (9/4)^2
Which means that you need 5.0625 kg per meter.

If you're being generous, that would mean that you'd rap the linear cutting charges around the hole 5 times, for 20 meters and 20 kilograms of explosives. Of course, technically, that's a bit shy of what's actually needed, so cruel GM's would make you wrap it around 6 times for 24 kilograms of explosives.

Now, say that you took that same linear cutting charge as a breaching charge. The calculation would be almost the same as before, except that the armor on the door drops by 5.

(.5 * 9) + (3 / 4)
(4.5) + (.75)
5.25 or 6 DV

So, you need 6 DV to create a 1 meter wide hole.

6/1/4 = 1.5
1.5^2 = 2.25 kg

2.25 kg is a lot smaller than 20-24 kilograms.

So, um, yeah. There's a hole in the explosives rules.

[TheOneRonin]

OneRonin: I reread the rules for breaching/cutting and I think you're right- there is something a little off about the amount of standard explosives.

Have you done the calculations using the linear cutting charges? Maybe the rules were written with those in mind, though it seems odd that cutting charges are always considered untamped. When you read the description of the cutting charges it sound like they have built in tamping (the angled iron that "focuses the explosive blast onto the line to be cut"). Anyway that -5 AP will make some difference, but not enough to correct the massive amounts of explosives you need for cutting. Doesn't make much sense.

One thing I noticed was the note about rubble obscuring up to half of the hole you create with breaching. It gives the impression that breaching is a really messy affair, but cutting has no such rule. Maybe that is one distinct advantage to cutting but I don't know if thats worth the extra explosives either.

As far as the rules in Arsenal superseding the rules in the BBB- my interpretation was that the multiplier from the Positioning Table on page 90 basically replaces the "DV x 2 against barriers" from the BBB. In other words the BBB assumes that all charges are placed "Higher above ground than hole radius, untamped" (x2) for the sake of simplicity.

How about this? Let's treat linear cutting charge DV just like breaching DV, and assume that they automatically get the x3 DV multiplier for being above the ground and tamped. So we end up with the following math:

The DV formula for cutting is: (sqrt of kilos/meter)*(Rating of explosives) *(DV multiplier for above ground + tamped)
We also get 1 additional AP per net hit made on the demo extended test (assume no net hits, so no extra AP)
Base AP for Linear Cutting Charges is -5 AP

So the lowest rating linear cutting charge you can get is rating 4. And there is 1kg of explosives per meter.

So we have: (1)*(4)*(3) = 12DV. Our sec door has Armor 8 and Structure 9. With the -5AP from using a linear cutting charge, the door doesn't have enough dice to buy any hits, and our 12DV is more than enough to cut it. Of course, we do end up using 4kg of explosives, but that's not too bad.

If the cutting charges only had .56kg of explosives per meter, then we would come out RIGHT at 9DV. And we do it with a little over 2kg of explosives rather than 4. I could live with that.

So here are some sample numbers for cutting when using the 1kg linear cutting charges from arsenal, and assuming the x3 DV:


Heavy Material: Armor: 6 Struct: 7
Example: hardwood, dataterm, lightpost, chain link
*Rating 4 charges will do the job easily


Reinforced Material: Armor: 8 Struct: 9
Example: densiplast, security door, armored glass, Kevlar wallboard
*Rating 4 charges will do the job easily


Structural Material: Armor: 12 Struct: 11
Example: brick, plascrete
*Rating 4 with just barely do the job. 4 or more net hits on your demo test will guarantee it.


Heavy Structural Material: Armor: 16 Struct: 13
Example: concrete, metal beam
*Rating 5 will just barely do the job. 4 or more net hits on your demo test will guarantee it.


Armored/Reinforced Material: Armor: 24 Struct: 15
Example: reinforced concrete
*Rating 6 will work only if you get 4 or more hits on your demo test. Otherwise, you will need rating 7.


Hardened Material: Armor: 32+ Struct: 17+
Example: blast bunkers
*Rating 8 will work only if you get 4 or more hits on your demo test. Otherwise you will need rating 9.



That works for me.

[Earlydawn]

So, is the consensus that cutting is meant to be accomplished by cutting charges?

[TheOneRonin]

So, is the consensus that cutting is meant to be accomplished by cutting charges?

Well, according to Arsenal, you can use just about any sort of explosive for cutting. However, the Linear Cutting Charges in book are designed specifically for cutting, and automatically start with a -5AP, in addition to however many net hits you make on your demo test when setting them up. This assumes you are cutting holes into a relatively large and flat surface. I would imagine that meter-long LCCs wouldn't work very well if you are trying to cut something like a 10-inch diameter round concrete pillar.


Technically, you should be able to use foam/plastic explosive to cut as well, but should be considerably less effective than the LCCs. Though the rules as written in Arsenal don't really reflect that.


IRL, you can even cut with det cord, though the amount of explosives listed in det cord is so small that you need about 10 meters of it to do 2-3 DV, which is retarded. Though I haven't figured out how to better handle it. Det cord might work better with a set DV/meter rather than basing it of the mass of explosives.

[kzt]

There are two ways of using explosives to cut steel. You can blast cut steel, or you can cut it with a shaped charge. Blast cutting steel requires quite a bit more explosives than using a shaped charge, but making effective shaped charges, particularly things like linear and flexible linear shaped charges requires quite a bit of skill and they are usually factory made.

There are various techniques for blast cutting steel and they are adapted to different targets. Typically if you have the and target info time to build the proper explosive change you can do things like build ribbon charges that will blast cut it with much less explosives than needed for brute force solutions. It's still more explosive and weight than you need for a linear shaped charge.

To fiddle with the rules and verify the accuracy you'd have to sit down with a copy FM 5-25 or a good text on explosives and run some numbers, then convert them into SR terms.

The other issue you run into in real life is that you apparently can't blast cut some metals, like Nickel-Molybdenum steels.