Firearms: Calculating active points from kinetic energy

[k1ll0tr0n]

Short version: a good simple way to get realistic active point totals for firearms is to take the 5 root of the muzzle energy (in ft/lbs), multiply by 6 and add 5. In excel, that's =PRODUCT(ME^(1/5),6)+5 where ME is the muzzle energy. If you want a curve that yields more powerful guns, do the same but with 4 root, i.e. =PRODUCT(ME^(1/4),5)

 

Long version: Sorry for this wall of text

 

I am a giant military nerd. Traditional HERO gun damage tables, based on caliber, have always left me a little flat. After fiddling with Excel and Wikipedia data I think I have a good curve based on energy:

 

This curve follows the HERO chart range

(MUZZLE ENERGY(ft-lbs)^(1/5))*5= ACTIVE POINTS

But, if you'd like to see more variation in the common calibers:

(MUZZLE ENERGY(ft-lbs)^(1/4))*5= ACTIVE POINTS

 

Either way, the players can stat out any gun they fancy

 

Both of these curves have points where they fall apart. The 5 root fail point is higher in the cannon range, 35mm and beyond. 4 root falls apart right after .50 BMG, which is usually at the top of a heroic-level firearm chart anyway. 4 root guns do well in grim game worlds, along with making combat much shorter (the two often go together).

 

You'll notice this doesn't quite take into account things like overpenetration. Smarter people than I have taken a stab at that, and while it's a very clever implementation, it adds another layer to what is already considered a complex system. It's hard enough to sell my new group on HERO as it is. You also get into issues of what's important to you in game versus what's important to you in the real world. In the game, you'd probably prefer to take a few body than to be STUNNED. But in the real world, you would (I assume) vastly prefer to take a little break as opposed to losing a finger or a few cups of blood. Stopping penetration in the real world can easily lead to being knocked around a bit more, but any player is going to be annoyed if they pay points for a defense that gets them STUNNED more often.

 

One more thing: it's important for the GM to take the barrel length into consideration. If a player shows up with a 20 × 110mm Hispano pistol and claims the full muzzle energy, it would be cool for the GM to call foul on that. Along these lines, STR MIN calculations should also be checked and common sense used. Even if a character has a 30 STR, they do not weigh enough to anchor an autocannon firing light antiaircraft rounds. It will literally pound them into the earth.

 

Anyway, hope someone finds this interesting, and possibly useful. Next up for me: finding some Star Wars Hero prefabs. Older links in the forums appear to be broken. Unhappy face.

CartridgeEnergy.txt

[Christopher R Taylor]

Its an interesting examination, something I'd like to see attempted with melee weapons and muscle powered ranged weapons as well.  I wonder if the system would function with a longbow?  A good english yew longbow would generate 105 lbf, according to Wikipedia (yeah I know but usually on this kind of topic its tolerable).  A hunting bow was a modest 50-60 lbf, and Crossbows can range up to about 130 lbf.

 

This site has some useful data on kinetic energy of old weapons

 

I'd run the numbers but frankly I don't even know how you'd do a factor with a fraction in it.

[NuSoardGraphite]

Your text file has formatting issues.  It's impossible to read as it is now.  It would be better served as an excel file or created under Word using a Table format.

 

Many people have taken a stab at what you are attempting here.  Most ended up checked into the looney bin.

 

The major contention when it comes to developing "realistic" firearms rules in Hero is that the original authors created Hero with a basis of X2 energy (force/damage/KE/whatever) equals +1 damage class.  Everything in the damage system including Defenses and the Body of objects is based upon this exponential progression.  The problem is that the original authors never bothered to tell anyone this fact and left the fanbase to argue over this interpretation of the rules.  At this juncture, the general consensus is that the damage system is exponential in nature and x2 energy equals +1 Damage Class, but there are still quite a few holdouts who don't adhere to this formula.  They tend to prefer the notion that the damage system is abstract.  This tends to lend itself more to Superheroic genres than to those who prefer Heroic genres.

 

I personally use a simple KE to DC chart that places the Damage Class based on the Muzzle Energy of the round.  Every doubling of energy is +1DC.  50 to 100J is 1DC.  Go from there.  That puts the .50 Desert Eagle at about 6DC or 2D6K.

[Christopher R Taylor]

So with 1 foot pound equaling roughly 1.35 joules, your system would place a hunting bow around 1 point of body damage, which seems kind of low to me.

[NuSoardGraphite]

So with 1 foot pound equaling roughly 1.35 joules, your system would place a hunting bow around 1 point of body damage, which seems kind of low to me.

Muscle powered weapons should not use the same calculation to determine damage as projectile weapons. Trying to do so creates some rather frustrating inconsistancies. You can use the chart for a close approximation of where beam weapons should be based on their output power (convert Watts to Joules)

[Lucius]

 

I think I'll stick to calculating Active Points by adding up the Base Cost of the Power and the Adders and then multiplying by 1+Total Advantages.

 

Lucius Alexander

 

The palindromedary wants to calculate Inactive Points

[Tasha]

Also, not really worth it because it doesn't really take into account things about the Size and shape of the round.

 

On top of that, it seems like on of those exercises that leads to excessive work for minor gain.

[Markdoc]

Not only is there minor - if any - gain, but in real life there does not seem to be any direct connection between kinetic energy and actual damage. Too many other factors are as least as important. A perfect example are the amateur rail guns you can see in action on youtube. ENORMOUS muzzle energies, and yet most of them can't shoot through a cardboard box, because the round they fire is so light that it has little momentum.

 

So it's a lot of work to get an unrealistic result. The problem with bows illustrates that nicely, as does real life shooting data, where there's no discernible difference across a wide range of calibres and muzzle energies.

 

Cheers, Mark

[k1ll0tr0n]

Not only is there minor - if any - gain, but in real life there does not seem to be any direct connection between kinetic energy and actual damage. Too many other factors are as least as important. A perfect example are the amateur rail guns you can see in action on youtube. ENORMOUS muzzle energies, and yet most of them can't shoot through a cardboard box, because the round they fire is so light that it has little momentum.

 

So it's a lot of work to get an unrealistic result. The problem with bows illustrates that nicely, as does real life shooting data, where there's no discernible difference across a wide range of calibres and muzzle energies.

 

Cheers, Mark

First off, hat tip to Mr. Graphite for solving it elegantly with the exponential scaling. I consider my question answered. Eyeballing Mr. Graphite's solution, using 50 ft-lb as a baseline for 1d6 RKA, I get superior values to what is in the stock firearm tables. That would make small arms top out at 4d6 RKA for the special-built Steyr AMR, which sounds right to me. And without Excel!

 

Mark, what amateur rail guns have you seen with high kinetic energy? That would be fascinating. I believe that energy combines mass and velocity, although the two become interrelated at relativistic velocities.

 

There are many, many other factors in bullet trauma, but the rest of them I am comfortable leaving them to the dice (AKA "the STUN lottery"). I definitely don't want a lot of complexity, and definitely no added rules to what's already an admittedly thick ruleset- at least for newer players.

 

As someone mentioned, yes, for human powered weaponry, trauma has much less to do with energy. Slashing in particular is quite hard to model. Speaking for myself, however, I feel HERO mechanics for hand-to-hand are quite solid, and haven't ever really had a "What the . .?" moment there.

 

Thank you everyone! Good to be here.

[Markdoc]

A quick google search for 'amateur railgun' will turn up plenty of videos and websites, but most of these are small railguns that can safely be fired inside despite their very high muzzle energies.

 

But if you want see a state of the art amateur rail gun, try these guys: http://hybridtechcar.com/railgun-27-kilojoules-the-most-powerful-amateur-railgun/. It fires a big-ass projectile, with a muzzle energy of 27,000 joules. For comparison, that's (very roughly) about twice the muzzle energy of a 0.5 HMG. The projectile can penetrate a single car door or about 20 cm into ballistic gel, so the lethality if you fired it at a person is probably a little greater than a .38 short (less penetration, but it would make an ugly wound with that projectile). It kind of makes the point eloquently that muzzle energy doesn't really tell you much about a weapon's lethality or ability to inflict damage.

 

There's a reason that balistic wound specialists gave up on measuring KE as a predictor of weapon lethality a couple of decades ago: it doesn't map at all well to real life shooting data. I talk about this in more detail (with data links) on a recent thread in this forum called "are tanks really that tough" but the topline message is that while there are clear diferences in lethality between handguns and long arms, the differences between handguns or between long arms is so small that it's very difficult to measure, even averaged out over hundreds of shootings. In hero terms that means that similar weapons (for example, handguns) all fall into a DC, or if you stretch it to the limits of credibility, at most 2DC of each other.

 

I'm a very data-driven guy, so the real life data for me, trumps the ability to differentiate weapons for gaming purposes, even though I know a lot of players (including me, it must be admitted) like that

 

Cheers, Mark

[NuSoardGraphite]

A quick google search for 'amateur railgun' will turn up plenty of videos and websites, but most of these are small railguns that can safely be fired inside despite their very high muzzle energies.

 

But if you want see a state of the art amateur rail gun, try these guys: http://hybridtechcar.com/railgun-27-kilojoules-the-most-powerful-amateur-railgun/. It fires a big-ass projectile, with a muzzle energy of 27,000 joules. For comparison, that's (very roughly) about twice the muzzle energy of a 0.5 HMG. The projectile can penetrate a single car door or about 20 cm into ballistic gel, so the lethality if you fired it at a person is probably a little greater than a .38 short (less penetration, but it would make an ugly wound with that projectile). It kind of makes the point eloquently that muzzle energy doesn't really tell you much about a weapon's lethality or ability to inflict damage.

 

There's a reason that balistic wound specialists gave up on measuring KE as a predictor of weapon lethality a couple of decades ago: it doesn't map at all well to real life shooting data. I talk about this in more detail (with data links) on a recent thread in this forum called "are tanks really that tough" but the topline message is that while there are clear diferences in lethality between handguns and long arms, the differences between handguns or between long arms is so small that it's very difficult to measure, even averaged out over hundreds of shootings. In hero terms that means that similar weapons (for example, handguns) all fall into a DC, or if you stretch it to the limits of credibility, at most 2DC of each other.

 

I'm a very data-driven guy, so the real life data for me, trumps the ability to differentiate weapons for gaming purposes, even though I know a lot of players (including me, it must be admitted) like that

 

Cheers, Mark

This bears out with my KE damage model in that a .38 pistol does 3 DC and a .50 Desert Eagle or a 7.62mm from an AK-47 does 6 DC. Only being 3 DC apart... 1d6k vs 2d6k. Not much of a difference. The biggest thing being the higher energy rounds penetrate armor better.

 

Inwould like to know what kind of projectiles the railguns are firing and dona comparison with similar size, shape and grain of projectile between a conventional assault rifle like the M4 and a railgun.

 

Ah, it seems they are using Aluminum rounds, which dont seem robust enough to survive the impacts. I would like to see then use smaller steel or iron projectiles and compare penetration characteristics. I'm sure they would achieve wildly diffferent results. In fact the aluminum rounds are so delicate, at least on one occasion the aluminum round melted from the friction and got stuck in the barrell. Not good!

 

So yes, testing with comparable ammo mass and density would be necessary for comparison purposes.

[Christopher R Taylor]

The thing is, if you're careful with the armor in games, 3 damage classes can add up to an awful lot.  A max of 8 rPD in a game means a 1d6 bullet will never penetrate to do body damage, but a 2d6 will often do considerable body damage.  Its about designing all the parts to work together and "break points" where defenses no longer protect but damage keeps going up.

[NuSoardGraphite]

The thing is, if you're careful with the armor in games, 3 damage classes can add up to an awful lot.  A max of 8 rPD in a game means a 1d6 bullet will never penetrate to do body damage, but a 2d6 will often do considerable body damage.  Its about designing all the parts to work together and "break points" where defenses no longer protect but damage keeps going up.

Absolutely.

 

In Heroic level games, the GM should control defenses so that they can get the proper feel they desire. The importance of balancing DC vs Defense cannot be stressed enough.

[Markdoc]

Ah, it seems they are using Aluminum rounds, which dont seem robust enough to survive the impacts. I would like to see then use smaller steel or iron projectiles and compare penetration characteristics. I'm sure they would achieve wildly diffferent results. In fact the aluminum rounds are so delicate, at least on one occasion the aluminum round melted from the friction and got stuck in the barrell. Not good!

 

Well the video shows very clearly indeed that the projectiles survive impact entirely intact - even the one that was fired through the car door, so no, that's not the reason.You are right that different projectiles would almost certainly change the outcome of the tests ... which right there tells us that kinetic energy is in fact, not the determining factor, since different projectiles with the same KE will behave differently.

 

As to the fact that 1d6 is not different to 2d6 .... actually that's a huge difference. In hero system terms the first will never penetrate normal ballistic armour while the second will do so routinely.  That's a far, far larger difference than that observed in real life with handguns of any calibre - that's actually about the magnitude(or a bit larger) than the real-life difference observed between handguns and mid-large calibre rifles.

 

regards, Mark

[Tasha]

Isn't there already a 50+ page discussion on the Dark Champions board about this kind of thing?

[NuSoardGraphite]

Well the video shows very clearly indeed that the projectiles survive impact entirely intact - even the one that was fired through the car door, so no, that's not the reason.You are right that different projectiles would almost certainly change the outcome of the tests ... which right there tells us that kinetic energy is in fact, not the determining factor, since different projectiles with the same KE will behave differently.

 

As to the fact that 1d6 is not different to 2d6 .... actually that's a huge difference. In hero system terms the first will never penetrate normal ballistic armour while the second will do so routinely. That's a far, far larger difference than that observed in real life with handguns of any calibre - that's actually about the magnitude(or a bit larger) than the real-life difference observed between handguns and mid-large calibre rifles.

 

regards, Mark

Aside from KE however, what factor in bullet physics can be used to determine the basis for damage?

 

For my purposes, I use KE as the basic factor for Damage class, then use other factors such as the shape of the round, density, momentum, bullet size etc to make adjustments to the base. For example a high densisty round with a thinner profile would be Armor Piercing. A round designed to mushroom when it hits flesh gets +1 DC and +1 StunX, but is Reduced Penetrating. Perhapse a low density round which has high velocity but lacks momentum is Reduced Penetrating.

[Markdoc]

Yup.

 

Cheers, Mark

[massey]

Well, part of the problem is Body.  The Body characteristic is a very vague thing.  Living creatures tend to have more Body than inanimate objects.  A normal can have 20 Body, which is enough to survive being shot in the forehead by a .50 cal rifle that rolls max damage.  You'll be bleeding to death, but you're still breathing.  If a doctor gets to you, you'll probably survive.

 

It's really just D&D hit points all over again.  Not that there's anything wrong with that -- it's perfect for a game.  But when you're trying to make firearms in the game work like they do in real life, you have to remember that the human body in the game doesn't work anything like the human body in real life.  Not to mention things like the Deadly Shot talent, where you just do more damage, because you do more damage.

[Markdoc]

Aside from KE however, what factor in bullet physics can be used to determine the basis for damage?

 

After firing more bullets into more things than the most enthusiastic gun nut will see in an entire lifetime, and going in detail through the entire shootings databases and extracting real life shootings where the weapon and ammo could be identified, the FBI ballistics team found only two things that predicted lethality: depth of penetration and location of the hit (not surprisingly, head hits are far more likely to be lethal than foot hits, for example). They also noted that handguns that produced hits that reached or exceeded 16" (40 cm) depth in ballistic gel were likely to penetrate right through the body cavity and that beyond that, there was no significant difference in lethality. Most modern handguns reach or exceed that baseline, which would imply that they are all similarly lethal ... and that's what their analysis of the shooting database showed*. Long arms were significantly more likely to inflict lethal hits than any handgun, and again, there was little observable differences between different long arms. Other factors (muzzle energy, bullet weight, residual energy at 30 yards, etc etc) were analysed in detail - none of them showed any correlation with lethality.

 

That's also the conclusion from the published studies I linked to the last time we had this discussion, and it's true of both homicide injuries in the US and conflict injuries among British soldiers.

 

So in conclusion, if you and your players like using KE to model damage for firearms, sure, knock yourself out. As Massey notes, BOD is a fairly abstract quantity anyway, and using KE to estimate weapon damage is no more unrealistic than people who can fly or shoot energy beams out of their eyes. But it is a game construct - it absolutely does not model what we see in real life (at least as regards shooting people).

 

That said, Tasha has a point. We're not really discussing Hero system mechanics here anymore so perhaps we should let his lapse here and take it up in the Dark Champions forum if there is any  interest in discussing it further.

 

cheers, Mark

 

*Edit: the firearms analysis program is ongoing, but the head of the program noted a while back that they were looking for the tiniest differences, saying that even though the difference might matter 3 times in a thousand, that 3/1000 chance could still save law enforcement officers' lives. That gives you an indication of the scale of the difference they .are looking at - about 1/3 of a percent, which is way, way less than a DC.

[NuSoardGraphite]

Well, part of the problem is Body. The Body characteristic is a very vague thing. Living creatures tend to have more Body than inanimate objects. A normal can have 20 Body, which is enough to survive being shot in the forehead by a .50 cal rifle that rolls max damage. You'll be bleeding to death, but you're still breathing. If a doctor gets to you, you'll probably survive.

 

It's really just D&D hit points all over again. Not that there's anything wrong with that -- it's perfect for a game. But when you're trying to make firearms in the game work like they do in real life, you have to remember that the human body in the game doesn't work anything like the human body in real life. Not to mention things like the Deadly Shot talent, where you just do more damage, because you do more damage.

And this is exactly why the Impairing and Disabling optional rules are a thing. So people in Heroic genres dont get shot in the head,and,just walk away from it.

 

To me, that is the other half of the equation. Bullet physics can only account for how the round delivers damage. It cannot account for how the object being hit by the bullet reacts to that damage. Thats why damage systems need to remain relatively abstract.

 

Damage dice and advantages/limitations is how damage is delivered. Body stun and impairing is how flesh reacts to being damaged. And honestly I think thats about the best we can hope for if we want to maintain any reasonable level of playability.

[Lucius]

Aside from KE however, what factor in bullet physics can be used to determine the basis for damage?

There's a rule requiring you to use some factor in bullet physics to determine the basis for damage?

 

Lucius Alexander

 

There is no rule requiring me to use some factor in the content of the post to determine the basis for the palindromedary tagline.

[NuSoardGraphite]

There's a rule requiring you to use some factor in bullet physics to determine the basis for damage?

 

Lucius Alexander

 

There is no rule requiring me to use some factor in the content of the post to determine the basis for the palindromedary tagline.

Not at all. Just wanting to do so for consistency and the ability to convert real world and fictional weaponry to game stats and have them stated appropriately.

[Hugh Neilson]

Not being any expert in firearms, "Aside from KE however, what factor in bullet physics can be used to determine the basis for damage?" sounds like the answer is "Real world analysis demonstrates that damage is not a direct function of KE", so why should it be the factor used to determine the basis for damage?

[Lucius]

Aside from KE however, what factor in bullet physics can be used to determine the basis for damage?

 

 

There's a rule requiring you to use some factor in bullet physics to determine the basis for damage?

 

 

Not at all. Just wanting to do so for consistency and the ability to convert real world and fictional weaponry to game stats and have them stated appropriately.

 

I don't see anything inconsistent in not using some factor in bullet physics to determine the basis for damage; I don't see where USFIBP is necessary to convert real world and fictional weaponry to game stats; and I'm afraid I don't know what you consider appropriate, but would be curious to hear you explain it.

 

Lucius Alexander

 

But I almost always consider a palindromedary tagline to be appropriate

[Tasha]

Not being any expert in firearms, "Aside from KE however, what factor in bullet physics can be used to determine the basis for damage?" sounds like the answer is "Real world analysis demonstrates that damage is not a direct function of KE", so why should it be the factor used to determine the basis for damage?

 

I think that KE is only one part of the equation when it comes to how a projectile damages tissue. Projectile shape, speed, composition, and many other factors contribute to damage. Also, it's possible for a projectile to go right though a piece of tissue not doing nearly the damage that it would do if it were moving slower or had bounced off some bones.

 

Most people play Hero to experience Cinematic Realism. Basically bigger guns cause more damage than little guns, there is room for custom ammo that does different things to damage. I don't think that any of us want to play Projectile Physics Hero, where we have to work out each gun and ammo type with tons of math. This is a Roleplaying game, there's bound to be some abstraction with the system. It's up to us and our players to figure out if this works for us.

 

This is one of those discussions that seem to come up regularly esp from Players who want more "realism". It almost always turns out that adding that realism either doesn't work at all because real life is really complicated or because the existing systems are surprisingly close enough to reality to satisfy most people.