Just How low IS "Low Recoil"?

In TML note 1856, Adrian Hurt [email removed] writes:

> > MT does NOT list gauss weapons as being "recoilless".  They list them as
> > being "low recoil", which is appropriate.  If you consider both F=ma and
> > Newton's 3rd Law ("Equal and opposite reaction") then the amount of enery
> > delivered to each gauss needle (and thus acceleration, since the needle's
> > mass is constant) is equal to the amount of recoil energy delivered to
> > the gauss weapon firing the needle.
>
> Time for some number crunching.  First, a correction to the above.  It's
> momentum, not energy, that Newton's 3rd law deals with.

You're picking nits, Adrian.  Assume the following symbols:
        m = mass of the gauss needle
        a = acceleration of the needle at the barrel mouth
        M = mass of the gauss rifle
        A = acceleration of the rifle in the opposite direction
If ma=F->, then MA=<-F, right?  By definition, "Momentum" is the magnitude
of F, without the vector component (staight out of Halliday & Resnick's
"Fundanemtals of Physics").

>                                                          Figures for
> Traveller assault rifle and gauss rifle come from Book 4; figures for M-16
> assault rifle come from "The Armory" by Kevin Dockery, in brackets in the
> assault rifle part for comparison.
>
>       Mass of a fully loaded assault rifle = 3.33 kg     (3.635 kg)
>       Mass of a 6mm slug from assault rifle = 0.005 kg   (0.00365 kg)
>       Velocity of slug = 900 m/s                         (999.7 m/s)
> =>    Momentum of slug = 4.5 kg m/s                      (3.65 m/s)
> By Newton's 3rd law, momentum of rifle = 4.5 kg m/s in the other direction.
> =>    Velocity of rifle = 1.35 m/s                       (1.0 m/s)

These values are slightly off (you've listed the UNLOADED wt. of the M-16
and the slug velocity is a little low for a std. DoD issue M193 ball round),
but I accept your point.

>
>       Mass of a fully loaded gauss rifle = 3.90 kg
>       Mass of a 4mm needle from gauss rifle = 0.004 kg
>       Velocity of needle = 1500 m/s
> =>    Momentum of slug = 6 kg m/s
> =>    Momentum of gauss rifle = 6 kg m/s the other way
> =>    Velocity of rifle = 1.54 m/s
> =>    A gauss rifle is no more a low recoil weapon than an assault rifle.

Let's qualify that: it's no more low recoil that a 5.56mm assault rifle.
I don't argue this, ever.  The flaw in your argument is assuming that the
5.56mm assault rifle IS NOT ALSO A LOW RECOIL WEAPON.  It is, in fact,
just that.  Have you ever fired an M-16?  You can do it with one hand,
you know.  It has almost no kick.

If compare the M-16 to a "real" assault rifle (my definition of "real";
you're mileage may vary), like the 7.62mm ARM/AR Galil, there's a noticable
difference.  Chambering the NATO M59 ball round, the values for it are:
        Mass of a fully loaded rifle = 4.07 kg (w/ loaded 35 rnd. clip)
        Mass of std. slug = 150.5 gr. = 9.75 g. = 0.00975 kg
        Velocity of slug = 2789 ft/s. = 850 m/s
        Momentum of slug = 8.29 kg m/s
using the same math you use (which I'm not contending, BTW), we get:
        Velocity of rifle = 2.04 m/s
This is about 130% that of the gauss rifle and the MT Player's Manual refers
to this type of weapon as "Med. Recoil" (see the entry "Assault Rifle (7mm)
on pg. 76).

Let's compare the momentum of the 5.56mm slug to a different, but popular,
American round: the std. .22 Long Rifle round.  According to "Cartridges
of the World" - 6th Ed., it has the following stats:
        Mass of std. slug = 40 gr. = 2.59 g. = 0.00259 kg.
        Muzzle velocity of slug = 1150 ft/s. = 350 m/s
        Momentum of slug = 0.908 kg m/s
Now, if we use that round in my Ruger 10/22 (a .22 semi-auto sports rifle),
which has the following weight:
        Mass of loaded rifle = 4.8 lb. = 1.8 kg.
We get a recoil momentum of:
        Velocity of rifle = 0.5 m/s.
Now, that's only about 37% of the M-16, and about 33% of the gauss rifle.
(I guess that makes it a "No Recoil" weapon.) :-)  The reason I include
this round is that I'd wager that almost everybody on the TML has fired
a .22 cal. rifle (or pistol) and some point in their life, so it gives
a common ground for interpretation.  The 7.62mm round fired by the Galil,
on the other hand, is a Winchester .308 round in civilian life; a big
game hunting round.  The 5.56mm M-16 is about in the middle, as is the
gauss rifle (although tending slightly towards the higher end).  This
pretty definitely puts both of them in the "Low Recoil" catagory, at
least by MT combat standards.

One last point, the MT Imperial Encyclopedia (pg. 71) states that standard
equipment for the gauss rifle includes gyrostabilization.  If that addition
doesn't make it "Low Recoil", then I don't know what does.

References for the weapons and ammo data:
        1) Modern American Weapons - edited by Ray Bonds;
                                Prentiss-Hall, 1986.
        2) Modern Land Combat - David Miller & Christopher F Foss;
                                Portland House, 1987.
        3) World Military Power - Chris Bishop & David Donald;
                                The Military Press, 1987.
        4) Cartridges of the World, 6th Ed. - Frank C. Barnes & Ken Warner;
                                DBI Books Inc., 1989.
        5) The Palladium Book of Contemporary Weapons - Maryann Siembieda;
                                Palladium Books, 1984.
                NOTE: I include this last entry only because it is a
                handy, fairly accurate, quick reference for an RPG.
                It is not a definitive source, by any means.

        Mark F. Cook

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