Result of firing Slug weapons in Micro or Zero G?

[Woas]

Last Wednesday I ran The Rescue, one of the free adventures found in Signs & Portents 55 as a one-off test-run of the Traveller rules system. We had a blast but a couple questions for us non-scientific minded people came up.

First odd part was during the rescue Herik the engineer who was trapped in a mine tunnel. For the characters to save him they need to navigate down an access tunnel that is in danger of cave-ins. The adventure states however that there is only 1/6th gravity. To my understanding that's about what the gravity on our moon is like. So I'm wondering how deadly would this be and how 'fast' are these rocks falling? A 200 lbs rock from the ceiling is only really 32 lb which would hurt if you threw that at me, but is it slowly drifting down and easily avoidable or what?
Our answer when I mentioned this was that the danger was a mix of falling objects and other debris in the tunnel getting kicked around and we just kind of went on. The one character who took damage grinned and bared it and it wasn't a big deal.

The next issue we ran into though was with guns, specifically slug throwers which brings me to the title and real root of this post. We're still in .16 G and now the player is up to the part where they are trying to rescue the space noble (his name escapes me) and run into some kidnappers/murderers. The player got into a quick gun battle with these guys and had a Gauss pistol which he fired into an enclosed hall way. Even on earth the bullet is going to bounce off some walls but what about in 1/6th gravity? Are there any rules for that? Perhaps there was something in the combat section of the rules that I totally mind-farted on when I was reading it and don't remember it?
At the time it didn't occur to us but we realized it afterwards that firing slug bullets, in an enclosed space in micro gravity is probably pretty dangerous as the bullet will probably ricochet a lot more than what is typical on a 1G planet with the possibility of hitting the gunman himself... or any of the other targets in the hall (maybe even a window although I would assume glass that is part of an airtight chamber is probably real strong and can take a couple bullets).

Anyway despite those two questions like I said we all had a lot of fun with Traveller an are all looking forward to playing it in the near future and thanks for any insight you can pass on about this stuff.

 

[Infojunky]

At the time it didn't occur to us but we realized it afterwards that firing slug bullets, in an enclosed space in micro gravity is probably pretty dangerous as the bullet will probably ricochet a lot more than what is typical on a 1G planet with the possibility of hitting the gunman himself... or any of the other targets in the hall (maybe even a window although I would assume glass that is part of an airtight chamber is probably real strong and can take a couple bullets).

Unless you are in a circular hall it is very unlikely you will have to worry about a ricochet being hit by your own ricochet.

Ricochets depend on more on the striking angle of the projectile and less on gravity.

 

[lastbesthope]

Like infojunky says, ricochets are more to do with celocity and strike angle, which is more affedcted by air restsikstance than gravity, the lower gravity will reduce the 'drop' in the trajectory of the bhullet.

As for the falling rocks, in the lower gravity the acceleration due to gravity will be about 1.635m/s^2 instead of the Earth normal 9.81 m/s^2. They will accelerate at 1/6 the notrmal rate so over the same vertical distance will gain less speed, kinetic energy andf momentum.

And while a 200 lb (approx 90kg) rock will only weigh about 33 lbs in such reduced g, it will still mass the same 90kg. There are some things where it is the mass that is important (kinetic energy) and others where it is the weight (mg) like gravitational potential energy.

LBH

 

[EDG]

And while a 200 lb (approx 90kg) rock will only weigh about 33 lbs in such reduced g, it will still mass the same 90kg. There are some things where it is the mass that is important (kinetic energy) and others where it is the weight (mg) like gravitational potential energy.

Which is why astronauts have to be VERY careful when manoeuvering multi-ton satellites. Sure, it may feel like it weighs only a few kilograms in weightless conditions, but it still has a multi-ton mass, which means it can still slowly crush a person to death if they're pinned between it and a wall.

 

[Woas]

For the ricochet, I didn't mean hitting your own bullet with a stray bullet. The situation was something like:

Character walks through a doorway and into roughly the middle of a relatively bare hallway. There is about 30' of hallway to his left and right and down on the right there are 4 guys standing, trying to break into a door and all huddled around it. Character takes aim with his Gauss pistol and opens up aiming his gun down the hall way.

Now, the bullets are flying pass the guys 30' and hitting the end of the hallway, the floor, ceiling, and side walls I assume (he's auto firing) at all sorts of potential angles. With only 1/6th G pulling the bullets 'down' what is going to stop the stray bullets from going past the the target (the thug guys), hitting a surface at an odd angle behind them and bouncing back down the hall way.

What you're saying is that the bullets are more likely to dent and burrow into the wall making bullet holes anyway and not ricochet?

I ask because I am probably the least scientifically/mathematically/physics inclined person around here and am just trying to wrap my head around how things happen IN SPAAAAACE! :wink: As I have never been there. So I apologize for the ignorance.

I some searching about Mass and Weight and was enlighten. At first I thought you were crazy EDG... I mean, if something is weightless how could it crush someone. They could just 'pick it up'. But I checked some rudamentary high school science class websites and understand now. 8)

 

[lastbesthope]

What you're saying is that the bullets are more likely to dent and burrow into the wall making bullet holes anyway and not ricochet?

Due to being in reduced gravity? No I'm not saying that and I don't think anyone else is.

Ricochets, while obviously affected by gravity are more affected by the velocity of the bullet on impact and the nature of the impact surface. Gravity only plays a very minor part in that due to it's effect on the overall trajectory of the bullet.

LBH

 

[zanwot]

Concerning bullet paths, and ricochets:

When a scientific says that something is negligible, or has a minor effect, it means you should basicallly ignore it, completely. Scientifics have a tendency of being nitpicky. (I should know)

So when it is said that the effects of gravity on bullet paths and/or ricochets in a closed volume can be ignored, or is minor, it means forget the effects of gravity (or the lack of it) completely.

In a spacestation/ship/base, concerning bullets and ricochets, everything would be exactly like what would happen in a submarine. For all intent and purposes, gravity (or the lack of) has no special effect. As in: with or without gravity does not change anything. Ricochets happen, and are only a function of: the type of bullets, the angles to the surfaces (ricochets happen when bullets do not hit a surface too straight on), and the type of surfaces. Like in a submarine. (submarine is a good analogy, better than planes, because they have to be really well protected from the outside environment, just like in space)

 

[Infojunky]

Now, the bullets are flying pass the guys 30' and hitting the end of the hallway, the floor, ceiling, and side walls I assume (he's auto firing) at all sorts of potential angles. With only 1/6th G pulling the bullets 'down' what is going to stop the stray bullets from going past the the target (the thug guys), hitting a surface at an odd angle behind them and bouncing back down the hall way.

What you're saying is that the bullets are more likely to dent and burrow into the wall making bullet holes anyway and not ricochet?

Yes, in simple terms.

Have you every skipped stones on a pond? Angle of interaction is everything, for a ricochet to happen in general the angle of interaction between the projectile and the surface needs to be under 45 degrees, the shallower the angle the more likely said projectile will skip (ricochet). The general angle of the projectile leaving the interaction will be very similar to the angle that it entered with. i.e. The projectile hits the wall at 37 degrees will leave that spot at 37 degrees.

I hope this helps.

 

[Woas]

I guess we could also just assume that most slug projectiles this far in the future, that have the potential to be fired in vacuums and to avoid any chance at all for that one in a billion shot, would be frangible as well.

Thanks for the info guys.

 

[Cleon the Mad]

I guess we could also just assume that most slug projectiles this far in the future, that have the potential to be fired in vacuums and to avoid any chance at all for that one in a billion shot, would be frangible as well.

Thanks for the info guys.

No, why would the rounds at TL 12 or 13 (whatever TL the Gauss Pistol is again) have to be frangible? They might be, but probably wouldn't be the most common round sold, just like now. Even if they were, I think the rounds for the gauss small arms are hollow point rounds with a dense core, some sort of dense needle or ball in it for a penetrator. So even if the "soft" outer bullet was frangible, there would still be a small dense core.

Basically, what this boils down to is you're asking if shooting in a tight space in 1/6th gravity will cause more ricochets then normal? To slightly rephrase what others have said, for all practical purposes no. Or to put it another way, for the purposes of the ricochets only, ignore the gravity. Just decide if you feel the round(s) would ricochet in the room they were in just based on the size, the angle(s) the rounds would be hitting and so forth.

 

[AKAmra]

Now, the bullets are flying pass the guys 30' and hitting the end of the hallway, the floor, ceiling, and side walls I assume (he's auto firing) at all sorts of potential angles. With only 1/6th G pulling the bullets 'down' what is going to stop the stray bullets from going past the the target (the thug guys), hitting a surface at an odd angle behind them and bouncing back down the hall way.

What you're saying is that the bullets are more likely to dent and burrow into the wall making bullet holes anyway and not ricochet?

Yes, in simple terms.

Have you every skipped stones on a pond? Angle of interaction is everything, for a ricochet to happen in general the angle of interaction between the projectile and the surface needs to be under 45 degrees, the shallower the angle the more likely said projectile will skip (ricochet). The general angle of the projectile leaving the interaction will be very similar to the angle that it entered with. i.e. The projectile hits the wall at 37 degrees will leave that spot at 37 degrees.

I hope this helps.

I'm not a science guy, but I don't think bullets richocet at the angle they hit at due to deformation and other physics I won't pretend to understand. What I do know is when we train moving down a hallway in a potential firefight we are instructed to stay off the wall because a bullet that hits the wall will tend to continue skimming along the wall (within a couple inches), not bounce off the wall.

For gaming purposes, I'm also in the "ignore it, it's not worth worrying about" camp.

 

[zanwot]

I'm not a science guy, but I don't think bullets richocet at the angle they hit at due to deformation and other physics I won't pretend to understand. What I do know is when we train moving down a hallway in a potential firefight we are instructed to stay off the wall because a bullet that hits the wall will tend to continue skimming along the wall (within a couple inches), not bounce off the wall.

Interesting, thanks. I guess that is because bullets are deformed upon inpact, which means they loose most of their momentum perpendicular to the wall. If the bullets were ultra solid, spherical and un deformable (or more precisely prone to elastic deformation instead of irreversible deformation, even at those energies) they should bounce "properly" (if they do not shatter).

 

[Shiloh]

I'm not a science guy, but I don't think bullets richocet at the angle they hit at due to deformation and other physics I won't pretend to understand. What I do know is when we train moving down a hallway in a potential firefight we are instructed to stay off the wall because a bullet that hits the wall will tend to continue skimming along the wall (within a couple inches), not bounce off the wall.

I think the "bullets following surfaces" thing has a bunch to do with spin and surface drag effects; in effect the impact starts the (probably seriously deformed, yeah) bullet tumbling and it "cartwheels" along the surface.

But firing down a corridor, you won't get *any* bullets coming back your way. If they hit square enough to bounce back in anything like a reciprocal direction, they'll splat or penetrate.

 

[Infojunky]

I'm not a science guy, but I don't think bullets richocet at the angle they hit at due to deformation and other physics I won't pretend to understand. What I do know is when we train moving down a hallway in a potential firefight we are instructed to stay off the wall because a bullet that hits the wall will tend to continue skimming along the wall (within a couple inches), not bounce off the wall.

For the record Gunfights are chaotic events. In general I gave the basic state and reaction. Now if we want to get into the exact interaction of each slug we can, there will be variation due to the type of slug, the type of surface, the angle, the roll of the slug etc...

Or Take from me, I have used a shotgun it a steel corridor, bouncing shot from the deck into opponents legs is a common trick.

 

[captainjack23]

I'm not a science guy, but I don't think bullets richocet at the angle they hit at due to deformation and other physics I won't pretend to understand. What I do know is when we train moving down a hallway in a potential firefight we are instructed to stay off the wall because a bullet that hits the wall will tend to continue skimming along the wall (within a couple inches), not bounce off the wall.

For the record Gunfights are chaotic events. In general I gave the basic state and reaction. Now if we want to get into the exact interaction of each slug we can, there will be variation due to the type of slug, the type of surface, the angle, the roll of the slug etc...

Or Take from me, I have used a shotgun it a steel corridor, bouncing shot from the deck into opponents legs is a common trick.

Let me guess. Fleet marines ?


In any case, with regards to ballistics, , yes, the gravity only determines when it would hit the ground after being fired parallel to the ground. -which IIRC, is what defines point blanc - beyond this, you have to compensate for drop by firing above the target. Differing gravity will effect a bullets trajectory -on the moon, short range is very far indeed, and on Jupiter, much less (plus there's the getting baked,irradiated and crushed issue).

And, the projectile will still have most of its imparted velocity when it does hit (losing it only through friction of the medium -atmosphere or....well... meat :? ) and the occasional ricochet), While gravity would add to this, yes, it is miniscule compared to the velocity imparted by the propellant. And can be ignored.

Heres one example that I've never been able to get my monkey brain to accept but is true nonetheless - if you fire a bullet parelell to the ground and drop one at the same time, they'll hit the ground at the same time.
That's the effect of gravity.

 

[Infojunky]

Let me guess. Fleet marines ?

Nope, well kinda same Department different branch, Naval Special Warfare many moons ago.

 

[atpollard]

A slight topic drift, but still related ...

What reduced gravity WILL affect is aim. A long range rifle shot with a scope that would be a perfect chest shot in normal gravity, will sail over the head of your target in 1/6 gravity - the bullet didn't drop as much as the scope was set to compensate for due to the reduced gravity.

At 30 meters, a bullet hitting an inch high or low will probably not matter, but at hundreds of meters those inches will be feet off target.

In game terms, it means sights need to be reset for local gravity to be effective.