Home » MODDING HQ 1.13 » v1.13 Coding Talk » Lower bullet damage with distance
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| Re: Lower bullet damage with distance[message #294076]
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Thu, 24 November 2011 13:28  
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 usrbid |
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Messages:1506
Registered:December 2008 |
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Yo Monade, the amount of damage a bullet does depends on (as far as I know):
- bullet weight
- bullet speed (at a specific distance)
- bullet shape
- target medium
From weight and speed you will (probably) be able to calculate the energy the bullet has. However as far as I know the energy is not the best measure to determine damage. There is something called the Taylor KO Index (look on Google), which is better in predicting effect on impact.
The weight, speed, and energy for most bullets you can find on Wiki (or on the package when you purchase them e.g. Hornady is good about that).
For example shooting a typical 9mm and 45 ACP under same conditions, it is quite possible the 9mm will have more energy compared to the 45 (I haven't verified that), however from experience the 45 will have more destructive effects (I believe because the bullet is bigger and heavier).
A hollow point will penetrate less compared to a full metal jacket. For example shooting a 45 HP and FMJ under same conditions the FMJ will travel further in the medium.
Here is why energy alone is not a good measure. A 9mm FMJ will travel ~4 feet through ballistic medium (no denium in front), while a 45 FMJ will make it (I guess) ~18 inches (maybe more, but not 4 feet). The 9mm travels further because the bullet is smaller and there is less friction to slow it down.
However a front to back pass through is not as desirable. Depending what organs (if any) were damaged, this can be survivable. A 45 HP will lose all its energy inside the medium and cause a tremendous temporary stretch cavity and leave a huge wound channel which in turn speeds up blood loss.
Bullet speed at muzzle (right in front of the gun) is determined by the barrel length (using same bullets). Too short of a barrel doesn't allow all energy from the powder to be transferred on the bullet. Too long of a barrel (unlikely case) will eventually slow down the bullet due to friction in the barrel.
For example shooting a 45 ACP through a 5 inch barrel will have the usual 890 ft/s at muzzle, shooting through a 3 inch barrel can make the speed drop below 800 ft/s. US soldiers in Iraq prefer 20 inch barrels for 5.56 NATO as the longer barrel gives the bullet more speed / destructive power.
Bullet speed at target is influenced almost entirely by air resistance, which in turn needs humidity, barometric pressure etc. For example most modern firearms e.g. Glock, H&K USP will discharge safely completely submerged in water, however the bullet travels about 2 1/2 feet in water.
Another example, the faster a bullet goes the more air resistance it will encounter. Speeding up a bullet to somewhere between 3,000 to 4,000 ft/s will result in the bullet disintegrating in mid air, it breaks up into pieces (assuming normal bullets, not tungsten core). That's why small arms ordinance typically doesn't go beyond ~3,000 ft/s.
Bullet drop is mostly an aiming challenge. The more a bullet drops, the higher you need to aim (or adjust the sights). For example 7.62x39 WP has a drop of ~40 inches (don't know the exact number) at 300 yards. However if you compensate for the drop by aiming higher, the bullet will hurt the target, no difference.
How much a bullet drops depends on its weight and the energy it has. Heavier and slower bullets will drop more.
The shape of the tip of the bullet will influence how much air resistance a bullet has. This is why hunting rounds are typically polymere (plastic) filled hollow points as you want good flight characteristics but destructive power at target. The plastic tip is no significant hinderance for hollow point expansion.
The shape of the nose of the bullet, the area immediately following the very tip, also determines air resistance. This "curvature" of the bullet is called ogive. This is why rifle bullets are shaped differently than handgun ammunition, because rifle bullets are designed to better deal with traveling through air over long distances.
The shape of the tail of the bullet will influence stability (wobble) and how well the projectile deals with "closing up the air" behind it, which is called drag. Basically the bullet makes a hole as it travels through the air which creates a (partial) vacuum at its end, which "pulls" the bullet back and slows it down. A boat tail design is typically used for long range high accuracy target engagement as the boat tail (look it up on Wiki) stabilizes the bullet and bleeds of drag well.
Let me know if you have questions.
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| Re: Lower bullet damage with distance[message #294078]
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Thu, 24 November 2011 15:50
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| Sam Hotte |
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Messages:1965
Registered:March 2009
Location: Middle of Germany |
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AFAIU all the stuff "how does any projectile transfer its energy to the target" is done already in MAM. So no need to duplicate this, IMO.
I do not know, if MAM considers range in its calculation ("how much energy has been lost flying between muzzle and target due to mainly so called air resistance?"). If not, there - the time of impact on target - is the right place to consider it if you want to have it as complex as MAM.
If you stick to the more simplified current damage system AFAIK "bullet drop" of NCTH is the part that considers range restrictions due to air resistance. I guess that range currently just influences CTH.
You would need something added like "for every tile the bullets goes over effective range its potential damage is reduced by x".
That'd be it, IMHO.
[Updated on: Thu, 24 November 2011 17:32] by Moderator Report message to a moderator
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Sergeant Major
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| Re: Lower bullet damage with distance[message #294088]
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Thu, 24 November 2011 20:21
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| Sam Hotte |
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Messages:1965
Registered:March 2009
Location: Middle of Germany |
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MonadeThe point is just we have no dynamical calculation of damage loss with distance.
But we have a dynamical calculation of Damage: MAM. (Let's assume for the discussion MAM would be a physically accurate calculation of each bullets damage depending on weight, form and shape, material etc. - and impact energy)
The only significant influence range has is a loss of impact energy.
MAM already calculates impact energy - but the energy loss the projectile suffers on its way is not calculated dynamically yet.(at least within effective range its not).
So what you need/want is a dynamically calculation of eneergy loss during the flight path. OK.
Given the fact that we do not have a weather and environmental simulation, we could take the very educated guess that the fluid "air" the bullet is flying through is the same in every part of the current tactical secter in game: Humidity, temperature etc. will not be different between two adjacent tiles and they will not change during the (very short) time period our bullet is on its way.
(So BTW your question about the impact of pressure, wind, temperature etc. is answered: They do not have impact in the game as they do not change during a gun fight - so you can take any values you see fit and being reasonable.)
After all, the only factors that then have significant influence on the calculation of a bullets drag (-> http://en.wikipedia.org/wiki/Drag_(physics) ) are its geometry and material and of course its initial speed.
And all those factors should be included in MAM for a good part at least. Cause Geometry of the projectile and its material determine things like tumbling, penetration, deformation etc.
That's why my POV is: If you want dynamically influence of range on damage, start at the point where damage is calculated dynamically; that's much easier than looking at the things from the IMHO wrong end (no offense intended).
[Updated on: Thu, 24 November 2011 20:26] by Moderator Report message to a moderator
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Sergeant Major
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| Re: Lower bullet damage with distance[message #294106]
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Fri, 25 November 2011 06:55
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| usrbid |
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Messages:1506
Registered:December 2008 |
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MonadeWow thanks Dieter
No problem, any time.
Monadewhat if the bullet is a Ricochet?
I am not super sure but I believe the current code doesn't support ricochets. In real life ricocheting does happen more frequently than one would expect e.g. deflection of stone or metal plate and the bullet is still dangerous e.g. you can find a couple NoobTube vids where the shooter gets minor injuries. Personally I ignore ricochets as the chance the bullet comes back at the shooter is abysmal.
MonadeAiming with subsonic ammunition at distances around 200 is something special than aiming with supersonic isnt it? As said the bullet drop is drastic compared to supersonic.
A heavy bullet will drop more compared to a lighter one given the same speed. That is also why hunting ammunition tries to be as fast as the bullet supports before disintegrating to make the bullet travel further in less time which in turn minimizes bullet drop and makes aiming easier.
This vid explains something else (how to zero your AR sights) but it visualizes very well how aiming and bullet drop works and will help you to actually see what we are talking about.
MonadeOne thing at the end: Air resitance is defiend by alot of parameters (wind, temperature, pressure...) which average value could be used for this?
In principle you can use any values you like e.g. averages at sea level, as the differences are almost negligable at shorter distances e.g. less than a mile, meaning air does a somewhat bad job trying to slow down a bullet. This is because a bullet travels comperatively slow e.g. to atmospheric entry where you need to become creative managing air resistance, and air is comparatively thin e.g. to water.
MonadeCan someone place a complete formula best with an example? Bullet x fired from weapon y has z engery left after xyz tiles.
You can get this information either from the Wiki (each caliber has the muzzle velocity and energy) for a "default" barrel length (usually 16 inch) or from the ammunition manufacturer (on their Web site or on the box the bullets come in). Here is something from Hornady for example. This is one of the free on-line calculator resources.
To get the velocity at a specific distance, there are many on-line ballistic calculators. You enter the bullet characteristics and shooting conditions, and the calculator will produce the data for a specific range.
Edit: None of the stuff on JBM is currently working, come back after the weekend, I am sure they are going to fix it soon, they have been providing this service for over a decade, must be a technical glitch.
[Updated on: Fri, 25 November 2011 07:18] by Moderator Report message to a moderator
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| Re: Lower bullet damage with distance[message #294156]
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Sat, 26 November 2011 18:45
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| Sam Hotte |
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Messages:1965
Registered:March 2009
Location: Middle of Germany |
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MonadeSam_HotteAs for air density I'd use basic barometric values (0
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Sergeant Major
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