"Paul J. Adam" wrote in message
...
In message ,
Ctenos writes
Is there a consistent basis for this designation in aircraft armament?

Not really. "Machine guns" traditionally went up to 12.7mm or 13.2mm,
"cannon" were 20mm and up, and there was sort of a grey area in between:
notably the Soviet 14.5mm and German 15mm weapons.

The Soviets started with an anti-tank rifle and used its ammunition for
a Really Heavy Machine Gun; the Germans made a 15mm weapon, then decided
that it would be better necked out to 20mm and firing bigger rounds with
more payload.

I believe the MG151/15 and MG151/20 were designed at the same time with the
same cartridge. The 15mm MG151/15 has a proportionatly longer barrel than
the MG151/20 to exploit the hot gases appropriatly and achieved a much
higher muzzle velocity. It had ballistics better than the US 50 caliber
with an explosive shell to boot. Pilots who used it in the early Me 109F
liked it because of its great accuracy and range. It lacked enough of an
explosive filling to damage the heavy bombers the Germans were encountering
so they had to resort to larger caliber weapons with lower muzzle
velocities. It was simply to hard to get enough hits to get a heavy down.
They needed about 20 hits of 20mm as it is.

The designation MG means "MachineGewher" or machine gun. It seems that
this ended at about 20mm
The designation MK means "MachineKanone" or machine canon. It seems this
started at about 30mm eg Mk 103 and Mk 108 which were the high and low
velocity 30 mm guns used by the Luwftwaffe. They regarded the Mk 108 as
firing 'mines'. They even had a hydrostatic fuse to detonate within the
fuel tank.
Only 3 hits were required to brring down a 4 engined heavy bomber and even a
P47 couldn't survive more than a hit or two. (which made the Me 109 so
deady if it got to within 200m) http://www.luft46.com/armament/mk108.html

At some point, around 50mm the designation changed the BK (Bord Kanon)
sometimes appeared. Believe it or not the Germans were planing to arm
their fighters with the 55mm Mk 112. It was a scaled up Mk 108. It was
actualy quite a feasigle weapon calculated to require only 1 hit. It was
low velocity but the shear size of the shell gave it reasonable ballistics.

There was also PAK (Panzer Abwher Kanone) literaly (tank anti canon) and
FLAK (Flugzeug Abwher Kanone) literaly (Flyingthing anti gun). FLAK has
ofcourse entered the english language.


(Though they called both MG151/15 and MG151/20 'machine
guns', as well as the 20mm MG/FF, further muddying the waters)


The MG/FF was a liscence or import of the Swiss Oerlikon 20mm used by both
allies and germans. It was recoil opperated and had a nice heavy shell but
its cadence and velocity was relative low. British AAA used a modified
version with higher velocity and even lower cadence (450rpm). It was
however simple, compact and reliable and it fitted into the Me 109s wing.
The Much Bigger compressed air opperated Mauser (known as the jack hammer
becuase of its sound to the allies) had to be slung under the 109s wings
becuase of the slats.


In terms of aircraft armament, it's gone away because 20mm is low-end
for fast-jet armament. Meanwhile, the old rule of thumb that you
couldn't get a useful explosive round in less than 20mm has been
overturned by Raufoss and their 12.7mm multipurpose round.

What makes this round supposedly effective? New more powerfull explosives?
Minaturised fuses?

During the Korean war Sabre pilots often observed their 50 caliber rounds
bouncing of Migs. The combination of extended ranges and thicker metal
skins meant that the standard 50 caliber round lacked the punch needed.



Basically, pick a position you like and stick to it




--
He thinks too much: such men are dangerous.
Julius Caesar I:2

Paul J. Adam MainBoxatjrwlynch[dot]demon{dot}co(.)uk