Why does Gauss Rifle = no recoil?

[drsarh]

Background (ignorable):
I recently moved out of the good old US of A (wife found a great job while I was in grad school, and hey - it IS Paris...) I have only recently discovered the existence of T20. Further degrading my existence is the loss of all of my old Classic Traveller and MegaTraveller tomes as a result of the move. Possibly my question has been answered elsewhere, or since I am working from the T20-lite (I have not yet found a source of the full book locally) it may be dealt with in the full rulebook. If it is dealt with elsewhere, then directions to the correct source are welcome! This leads me to the actual

Question:
What is the justification for the Gauss rifle having no recoil?

Analysis:
As I understand it, the Gauss rifle and it's near relative the EM rail gun use an intense electromagnetic field to accelerate a projectile to high velocity. Since the gun itself is the object that produces the accelerating EM field, the gun would experience the recoil. In the accelerator rifle, the slug is a small rocket (so it is the rocket exhaust that recoils), the snub pistol's muzzle velocity is low (so momentum p = m x v => low, but not zero, recoil) and laser weapons release a stream of photons with negligibly low momentum.

One might assume that the mass of the projectile is so low as to make the recoil from p = mv low. But then damage from it, also related to momentum, is also reduced.

Thanks
Sarh

 

[PapaGolfWhiskey]

Good Point Doctor. I'd like to see this one answered too.

BTW IMTU - The snub IS also (like the accelertor) a mini rocket gun.

 

[eclipse]

This was kicked around recently on the TML.
The short form of the answer is that it does have recoil, just not enough to be noticed by the game mechanics. If you search the archives for this month, you can probably find the thread with all the gritty, technical details.

 

[tjoneslo]

eclipse is correct in his brief statement.

Weapon damage is based upon kinetic energy: K=1/2mv^2, but recoil is based upon momentum: p=mv. The gauss weapon becomes a useful weapon because it uses a light weight (4 gram) projectile at very high velocity (>1500m/s). So the weapon can inflict a scary amount of damage without having an enormous kick to it.

Convential weapons also have additional kick from the gasses used to propel the bullet escaping from the end of the barrel. Since all of the mass of the powder used to propel the bullet comes out the end of the barrel, you must add this mass to momentum imparted to the gun. This second source of recoil kick is not present in the gauss gun.

http://www.travellercentral.com/rules/ke.html
This is a weapons design page which calculates recoil as well as weapon damage in various traveller versions. Play with it for a while to see how adding propellant mass dramatically increases the recoil.

 

[Rover]

My dear Travellers,
I had this very discussion a few days ago with the GM of my gaming group.

The answer we came up with is that a GR would have to have some form of gravetic inertia compensator, or other hightech wizadry.


A GR will have significant recoil.

I plugged the numbers into an online recoil calculator at http://www.geocities.com/CapitolHill/Lobby/1221/recoil.htm

Bullet Weight: 4 grams - 61.5 grains
Bullet velocity 1500m/s ~ 4875 fps
Weight of gun 5kg ~ 11lbs

total recoil 2.6 ft-lbs

An M16 would have about the same, but that is for just one round. This gets multiplied by the ROF, which for a gauss rifle would be quite high.

Now an M16 doesn't give much recoil, but if fired in zero g it would still be significant.

The thing is, I remember the muzzel velocity of the gausse rife being 4000 M/S (but I could be wrong on that)

If that is the case, the the recoil would be 18.4 ft-lbs. About the same as a 12ga slug. That would be too extream to handle on full auto in zero g.

 

[JeffSandmeier]

But as stated in an earlier post, there is no gas venting in a GR, as there would be in the M16. Therefore the actual recoil would be less, probably as much as halved.

 

[Rover]

Originally posted by AaronKohura:
But as stated in an earlier post, there is no gas venting in a GR, as there would be in the M16. Therefore the actual recoil would be less, probably as much as halved.

I took that into consideration when I made the calculation.

I did not to want to get too technical, but just point out that baring some techical wizardry there would be apprciable recoil with a Gauss Rifle. Remember Newton, For every action there is an equal and oposite reaction.

If you want to know all the numbers and plug them into an online recoil calculator, here they are.

Gause gun:
Bullet Weight: 4 grams - 61.5 grains
Bullet velocity 1500m/s ~ 4875 fps (I thought it was 4000 m/s or 13,000fps)
Weight of gun 5kg ~ 11lbs
Caliber 4mm or 0.157"

total recoil 2.59 ft-lbs

M16 (5.56 Nato, .223 Remington)
Bullet Weight: 55 grains
Bullet velocity 3200 fps
Powder weight 25.0 grains
Weight of gun 9lbs
Caliber 5.56 mm or .224" (That's the acual bullet diameter)

Total Recoil 2.68 ft-lbs

Now that's pretty much identical, for each bullet. The real differencs comes in rate of fire. the M16 spits bullets out at 800 rounds per minute. I would submit a gauss rifle would have a much higher ROF.

Now the high ROF will have the advantage of spitting the bullets out before the point of aim is too adversly effected by the recoil, but the total impluse imparted by the weapon to the shooter will be reletivly substantial.

In short a Gauss gun is not a zero G weapon.

And while we're on the subject of Gauss rifles, They are not silent. The high muzzel velocity will cause a sonic boom (in an atmoshere). The higher the velocity the louder the crack.

 

[Zutroi]

Misc. observations from the thread -

RE: the sonic boom.

If the target is missed, he won't hear the crack of the projectile until it has passed him, providing the interesting effect of making it sound like the gunfire is from the opposite direction. The unwary victim may even start to 'get away' from the fire by getting closer to the shooter, providing a better shot...

Recoil - Traveller gives 900 m/s as the muzzle velocity of an ACR (or 2740 ft/sec in American money), so the recoil of this weapon becomes a mere 2.3 pounds vs. the 2.6 of the gauss. Clearly they are in the same category, and the ACR needs to be recoilless, the gauss given a recoil value at least equal to the ACR, or proper tech invoked to explain the reason.

BTW, Garf, IMTU Snubs are rocket-rounds as well.

 

[drsarh]

Wow, thanks for all the info folks.

Sarh

 

[womble]

Felt-recoil is also affected by the length of the barrel of the weapon. Without having to have ejection ports or push the round forward of the clip to seat it in the breech, the gauss rifle is likely to have a longer barrel than its chemical equivalent.

Certainly the archetype I have in my head of the Traveller GR is a bullpup about as long as a WW2 bolt action rifle, making its barrel maybe 1.5 - 2 times as long and reducing the felt recoil by a like amount.

 

[Elliot]

Re Sonic Boom

I am no science boy or mathmo so I beg your indulgence to explain it to me...

It was always a CT/MT point that the GR was a silent weapon, the speed of sound being met in the barrel of the GR. This made the GR the assasins weapon. I don't know no science - so tell me: if the needle exceeds the speed of sound can it be heard by a target, or an onlooker.

Is there any signature in a GR? I figure that no gas explosion therefore no signature.

 

[Rover]

Originally posted by Elliot:
Re Sonic Boom
It was always a CT/MT point that the GR was a silent weapon, the speed of sound being met in the barrel of the GR.

IMHO this subject was not fully thought thru and adressed in the rules. Unless there is some sort of inertial compensator built into the GR, by the laws of physics it should have recoil.

As for sound. Even if it breaks the sound barrier in the barrel, the sonic boom still propogates with the projectile. The faster the projectile, the louder the sound. It would not be as loud as a full bore rile of today, but it would make a definite cracking sound.

In the RW guns equiped with silencers are rarely silent, just supressed. It's not like on TV and in the movies. In WWII the americans built a truly silent pistol. It was very large and fired a low powered sub-sonic bullet. The slide would lock so that it had to be manually cycled to avoid the noise the action made.

But of course Traveller is a game, not a simulation of the real world. Too much realism can bog things down. I know I don't like it in my gaming sessions when we get bogged down with arguments over what would happen in the real world.

 

[PapaGolfWhiskey]

OOH.. the Welrod.

And don't forget the DeLisle carbine.

A lee enfield body with a ton of sound baffles just to make a .45 acp round merely 'cough'

 

[Uncle Bob]

Womble, the barel length does not affect recoil except that it changes the weight and balance of the rifle, and we know what the weight is for Gauss Rifle.

I just checked Book 4, and Frank Chadwick does not say that the gauss rifle is recoilless. I thought he was too smart for that.

Where does the "recoilless" idea come from?
Who goofed?

 

[MichaelL65]

Originally posted by Dr. Sarh:
Question:
What is the justification for the Gauss rifle having no recoil?

There isn't one. The ref for the game I play in (SmilingDM on these boards) is one of the ones who protested it being listed as recoiless to begin with (it's fun to mention that the rule book says it's recoiless durring a game session - good for at least 5 min of distraction

)

 

[womble]

Hi Uncle Bob

Felt recoil is much more about Impulse than energy.

Recoil Impulse using the recoil calculator linked above gives:

GRifle: 0.0000428 lb-s
M-16: 1.3

A significant difference, you'll agree.

Impulse = Force x Time

Regardless of the method of propulsion, a force has to act on a bullet to do work to accelerate the bullet to its muzzle energy. The equal and opposite reaction to that force contributes to the recoil a shooter feels.

Work = J = energy

Work = Force x Distance

In a conventional firearm or gauss weapon, the work needed to accelerate the bullet to muzzle velocity can only act while the bullet is in the barrel, so

Distance=barrel length

So: Work = force x barrel length.

So: Work / barrel length = force

So: Muzzle energy / barrel length = force.

 

[Rover]

My Dear Wombol,

I don't think I follow your numbers.

Could you please respond with an example using the same numbers you did. When I calcualte the recoil I don't get anything near what you do.

 

[Keklas Rekobah]

I've fired a real-life 'gauss rifle' that had a similar muzzle velocity of a regular twenty-two calibre 'squirrel gun'. The round itself was also of similar size and mass.

The recoil of the gauss rifle felt more like a sustained surge than the jolt of the squirrel gun, even though the rounds left the barrels at the same speed.

By 'similar', I mean that the values were within 1.5% of each other.

(Hmm... 'Slug Throwers'... 'Squirrel Guns'... I wonder what the damage matrix looks like when the projectile is a small, slimy mollusc or a small, bushy-tailed rodent...?)

 

[womble]

projectile is a small, slimy mollusc or a small, bushy-tailed rodent...?

*Chuckles revoltedly*

 

[womble]

Hi Rover

I used this recoil calculator:

http://www.geocities.com/CapitolHill/Lobby/1221/recoil.htm

(originally posted by yourself...)

and must sheepishly agree, having put the very same numbers I thought I used this morning in, that the impulse figure for the grifle is near identical to that of the M-16 as calculated this morning... Don't know what I mistyped, but it is evident that I did mistype something... Apologies.

Nevertheless...

Making a barrel length estimate for the GR, by using the total length of an FN-FAL (1100mm) and using the barrel proportions of an SA-80 (518mm/780mm) gives a barrel length of 730mm, compared with the M-16's 508mm.

Muzzle energy for the GRifle = 0.5 * 0.004 * 1500 *1500 = 4500J

Muzzle energy for the M-16 = 0.5 * (55/61.5*.004) * 945 * 945 = 1600J

Hmmm. Looking shaky. The muzzle energy for the GR is so much higher that even with a barrel 50% longer the force required to accelerate it will be much greater. I withdraw my argument.