Path: utzoo!utgpu!watserv1!watmath!att!cbnews!military
From: bxr307@csc.anu.oz
Newsgroups: sci.military
Subject: Re: MG vs. Cannon
Message-ID: <1990Sep2.061024.3316@cbnews.att.com>
Date: 2 Sep 90 06:10:24 GMT
References: <1990Aug30.030107.29349@cbnews.att.com>
Sender: military@cbnews.att.com (William B. Thacker)
Organization: Computer Services, Australian National University
Lines: 39
Approved: military@att.att.com



From: bxr307@csc.anu.oz
In article <1990Aug30.030107.29349@cbnews.att.com>, dennett@Kodak.COM (Charlie Dennett) writes:
> 
> 
> From: dennett@Kodak.COM (Charlie Dennett)
> Sorry if this is an often asked or otherwise dumb question.  I've only read
> this group off and on for the last few months.
> 
> 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?

	The old classic definition was that anything below 15mm in calibre was
classed as a machine gun and anything above a cannon (regardless of whether it
fired an explosive round or not).  However with the introduction of the Soviet
14.5mm HMG that definition has become rather blurred.  The 14.5mm fires a HE
round but is classed as a HMG.  However by simply changing the definition to
differentiate between weapons which fire explosive versus solid rounds would
have trouble explaining the various small calibre cannon of 20-40mm which now
fire APDS/APFSDS/AP  round which are all non-explosive in nature.
	So it can be seen that it is difficult to decide what is a cannon and
what is a machine gun.  However I think the easiest way would be to simply have
a definition which depended not on the calibre of the weapon, or even on what
round it fires, rather the type of round which it fires most of the time. 
Therefore a 14.5mm HMG would be simply that, a HMG as it fires for most of the
time normal ball ammunition.  Whereas the 20-40mm cannons are cannons because
they fire a mix of HE/AP rounds usually with the HE predominating for most
missions (except in anti-armour).
	Both MG's and Cannons rely, at the moment on rifling in their barrels
to impart spin to their rounds.  However with the advent of APFSDS rounds for
30-40mm calibre guns promising quite good penetration I somehow think that the
rifling will soon be considered superflous for these weapons, just as it is now
for most tank guns (I wonder why the Brits are still sticking with a rifled
barrel for the 120mm?  Perhaps they know something other countries have
ignored? ;-)

Brian Ross