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Old 09-15-2019, 12:25 AM   #21
Rupert
 
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Default Re: Rounding DR and AD

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Wouldn't knockback be proportionate to the recoil? I've seen vids of people getting hit in the face from the recoil of firing a magnum, maybe those kinds of rounds might be able to knock back small animals with 3 HP a yard?
Getting hit in the face by a powerful handgun when you fire it is a failure of gun handling and recoil control. If you go backwards because it it, it's because you lost your balance when you tried to flinch out of the way of the gun (because you didn't want to get smacked in the face).
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Old 09-15-2019, 12:27 AM   #22
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Default Re: Rounding DR and AD

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In general, anything capable of being knocked back by a bullet will disintegrate when hit by one.
That's wildly hyperbolic.
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Old 09-15-2019, 01:35 AM   #23
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Default Re: Rounding DR and AD

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Getting hit in the face by a powerful handgun when you fire it is a failure of gun handling and recoil control.
Recoil-control is a skill which can prevent getting hit in the face, but ultimately it is the actual recoil which causes the gun to fly back when fired.

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If you go backwards because it it, it's because you lost your balance when you tried to flinch out of the way of the gun (because you didn't want to get smacked in the face).
You-as-a-whole, sure, but in terms of your hand/forearm's mass, pretty sure the recoil caused knockback.

So if a mouse weighs the same or less than your hand/forearm then shouldn't a bullet have enough force to knock it back?

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In general, anything capable of being knocked back by a bullet will disintegrate when hit by one.
I seriously want to see someone shoot billiards with a low-caliber pistol to see what happens.

I think there are plenty of hard light things that bullets could move around without utterly destroying. Humans just happen to be pretty big and soft compared to rocks.
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Old 09-15-2019, 01:39 AM   #24
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Default Re: Rounding DR and AD

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I think there are plenty of hard light things that bullets could move around without utterly destroying.
True, there are a decent number of inanimate objects that can handle it. Just nothing living.
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Old 09-15-2019, 07:29 AM   #25
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Default Re: Rounding DR and AD

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Recoil-control is a skill which can prevent getting hit in the face, but ultimately it is the actual recoil which causes the gun to fly back when fired.
A firearm that discharges while in the air is indeed going to be flung backward - as noted, a typical pistol bullet has somewhere in the neighborhood of 2.682kg*m/s, and by Newton that means the shot must impart the same to the weapon (well, the weapon may get a bit more, from pushing out gasses and unburnt powder after the bullet has already left the barrel, but I doubt itís enough to make much difference). A quick look online notes a Glock 21 is around 1 kg fully loaded, so it would fling the weapon back at over 2 m/s (indeed, itís nearly 3 yards per second). A GURPS average human would have an 8 lb or so arm (appropriate for a 150 lb person), which is 3.6 or so kg, meaning a decent grip would cut the above down to below 0.5 m/s, and good recoil control (which will involve actively using the muscles to slow the weapon down) will make it practically null.
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Old 09-15-2019, 09:15 AM   #26
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Default Re: Rounding DR and AD

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True, there are a decent number of inanimate objects that can handle it. Just nothing living.
Mythbusters did this (more than once). A 9mm pistol on the ground will indeed skid a yard or two.

A pig hung on a very sensitive hook and wearing an assault vest with an impovised trauma plate constructed from a slab of mild steel 3/4 inch thick shot witha .50 BMG rifle? It might fly backwards maybe 1 inch. The trauma plate is necessary to prevent overpentration with much energy being carried away by an exiting bullet. If you wonder, that trauma plate which the rules would probably put at DR 37 was pentrated with classical deformation and rupture. A sort of "volcano" shape.

That gun to the face? That's not "Knockback". When it occurs knockback in rules terms will cause the target to fly backwards 1 yard or more. No stumbling, no sliding, no falling, _flying_. What you're seeing in that "face" case is a Critical Failure result with a HT roll required by a hit to the Face Location with failure of that resulting in falling down.
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Old 09-15-2019, 09:32 AM   #27
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True, there are a decent number of inanimate objects that can handle it. Just nothing living.
Not even an abalone shot in the shell? They might be endangered (overfishing?) and require special licenses to catch them (apparently a black market for the meat) so it might be tricky to test that.

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Mythbusters did this (more than once). A 9mm pistol on the ground will indeed skid a yard or two.
Apparently those tend to weigh around 2 pounds? Not sure what ST/HP equivalent that'd be for a creature but sounds heavier than a mouse if not at rat.

Couldn't find the one you mentioned but https://www.wired.com/2014/02/hidden...ullet-baloney/ has an interesting thing about bent rifle barrels. I didn't think bullets could travel along such a curve! The kind of friction that would generate... wouldn't it slow down the round and heat up the barrel more than usual? Plus put stress along one side more than the other?

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The trauma plate is necessary to prevent overpentration with much energy being carried away by an exiting bullet.
Even for bullets which don't exit out the other side, I have to wonder, is it possible that actually penetrating a target (even if left behind in it) might somehow dissipate some of the backward force by the deformed tissue at the entry wound expanding outward?


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That gun to the face? That's not "Knockback". When it occurs knockback in rules terms will cause the target to fly backwards 1 yard or more. No stumbling, no sliding, no falling, _flying_.
I don't know that GURPS actually mentions the body must lose contact with the ground, even if the DX roll is failed and a fall results. I suppose because there's no increase to knockback for airborn targets that contact with the ground doesn't decrease it in any way, which seems strange.

Stumbling might fall under using "roll with blow" to voluntarily move backward with something, but conversely there doesn't seem to be a reverse skill where someone can attempt to halve (rather than double) knockback by leaning into a blow (perhaps increasing the damage?) rather than away from it.

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Originally Posted by Fred Brackin View Post
What you're seeing in that "face" case is a Critical Failure result with a HT roll required by a hit to the Face Location with failure of that resulting in falling down.
Obviously knockback isn't applied to limbs in isolation in GURPS terms but I just mean IRL you could consider the weight of non-tensed badly-aligned limbs to have their own independent inertias.
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Old 09-15-2019, 10:00 AM   #28
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.


Apparently those tend to weigh around 2 pounds? Not sure what ST/HP equivalent that'd be for a creature but sounds heavier than a mouse if not at rat.


Even for bullets which don't exit out the other side, I have to wonder, is it possible that actually penetrating a target (even if left behind in it) might somehow dissipate some of the backward force by the deformed tissue at the entry wound expanding outward?

A 2 lb animal would have maye 3 HP. That's half (round up) the figure for Machines on B.558. This largely agrees with the stats given for exampel animals elsewhere in Basic.

An small animal (like a prairie dog) struck by a high velocity but non-overpentrating rifle bullet such as the frangible bullets used in varmint rifles will literally explode. The temporary cavity caused by the wound will exceed the torso size of the prairie dog and the animal will burst with blood and stuff everywhere.

Only if the animal were bulletproof would it take knockback. An abalone shell or anything else organic is not nearly enough DR. If that nearly buletproof pig only had an inch or less of knockback from a .50 BMG you'd need soemthing like a DR40 animal 1/100th the pig's size to get significant knockback.

Bullets actually have very little momentum. They come out very high in kinetic energy because you square velocity in the KE equation. You don't square for momentum that's straight mass x velocity. So when you see a player get knocked back on the football field that's from something like 250 lbs at 20 feet per second. A rifle bullet like a 5.56mm might be 150x faster but it's 27,700x less massive. So the rifle bullet has 185x less momentum than the charging football player.
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Old 09-15-2019, 02:51 PM   #29
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Default Re: Rounding DR and AD

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Even for bullets which don't exit out the other side, I have to wonder, is it possible that actually penetrating a target (even if left behind in it) might somehow dissipate some of the backward force by the deformed tissue at the entry wound expanding outward?
The total momentum of the system is constant. The entire body moving back is one solution. The body mostly not moving and the bullet passing through unimpeded is another. The body mostly not moving except for a spray of blood and other materials out the back is a third. However, as long as the bullet is stopped and no material actually leaves the body, the movement of the body is constant.
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Old 09-15-2019, 04:09 PM   #30
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Default Re: Rounding DR and AD

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Originally Posted by Fred Brackin View Post
Only if the animal were bulletproof would it take knockback. An abalone shell or anything else organic is not nearly enough DR. If that nearly buletproof pig only had an inch or less of knockback from a .50 BMG you'd need soemthing like a DR40 animal 1/100th the pig's size to get significant knockback.
By significant do you mean 36 inches?

If, let's say, a policy was taken to treat 1 HP of blunt force trauma (ie taking 10 damage stopped by DR to create) as 1 crushing damage for knockback purposes, resulting in 1 yard for HP3 creatures, would that seem excessive?

For HP4 if using a formula like that, you'd need 2 HP for blunt force trauma, requiring 20 DR stopping 20 damage... for HP5 you'd need 30 DR, for HP6 you'd need 40 DR, and so on. With skinny/overweight variations of course.

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Originally Posted by Fred Brackin View Post
Bullets actually have very little momentum. They come out very high in kinetic energy because you square velocity in the KE equation. You don't square for momentum that's straight mass x velocity. So when you see a player get knocked back on the football field that's from something like 250 lbs at 20 feet per second. A rifle bullet like a 5.56mm might be 150x faster but it's 27,700x less massive. So the rifle bullet has 185x less momentum than the charging football player.
It doesn't exactly take a charging football player to throw someone off-balance though. I'll admit I haven't fired a gun to get a feel for that recoil. Maybe there's some way to hook up a spring scale to measure the max effective weight (via acceleration) created which could then be compared to the force of a punch?

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The total momentum of the system is constant.
The entire body moving back is one solution.
The body mostly not moving and the bullet passing through unimpeded is another.
The body mostly not moving except for a spray of blood and other materials out the back is a third.
However, as long as the bullet is stopped and no material actually leaves the body, the movement of the body is constant.
I guess I'm wondering if the widening of a wound to make room for a slug might make a body slightly wider and increase its air resistance, so even if the force remained equal, the air would oppose it more, resulting in slight distance reduction. Not with humans (I think tissue would just compress to make room) but maybe with some other kind of scifi creature with different composition.
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