Path: utzoo!utgpu!watserv1!watmath!att!cbnews!military
From: henry@zoo.toronto.edu (Henry Spencer)
Newsgroups: sci.military
Subject: Re: MG vs. Cannon
Message-ID: <1990Sep2.061010.3245@cbnews.att.com>
Date: 2 Sep 90 06:10:10 GMT
Sender: military@cbnews.att.com (William B. Thacker)
Organization: AT&T Bell Laboratories
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Approved: military@att.att.com



From: henry@zoo.toronto.edu (Henry Spencer)
>From: dennett@Kodak.COM (Charlie Dennett)
>Just what is the difference between a cannon and a machine gun (at least
>as it applies to planes?)  Does a cannon have a smooth bore and a mg
>have a rifled bore?  Does a cannon also have an explosive projectile?

I think the distinction was originally based on the ability to fire
an explosive shell.  There is otherwise no sharp boundary:  both have
rifled barrels, they often have similar mechanisms, rates of fire vary
widely (for example, the 20mm Vulcan cannon has a higher rate of fire
than any conventional MG), and muzzle velocities are not a reliable
guide.

In fact, it's more a matter of tradition than anything else.  As I recall,
the 20mm explosive cannon shell carries such a puny charge that it's not
often used, while the .50cal incendiary MG bullet is said to be very good
at killing aircraft.

Actually, there is a noticeable tendency in recent years to move away
from the borderline in any case.  Infantry and related weapons are moving
to smaller calibers, given the advantages of lighter ammunition and the
extreme rarity of long-range rifle/MG engagements; even 7.62mm is now
considered a rather large caliber.  Aircraft and antiaircraft weapons,
on the other hand, are growing away from the 20mm cannon, now considered
a bit small, towards 30-35mm, where explosive shells are really useful.
Actually, the 20mm cannon would probably be extinct in such applications
were it not that the US has so far been unsuccessful at developing a
bigger air-to-air gun for its aircraft.  Everyone else went to bigger
calibers long ago; about the smallest in use elsewhere is the Tornado's
27mm Mauser, and probably the best is Oerlikon's 30mm KCA.

                                         Henry Spencer at U of Toronto Zoology
                                          henry@zoo.toronto.edu   utzoo!henry