A big 20mm will not be useful with just two people and a mule available to lug it around - having a fully motorized and manned army was an exception in ww2, not a rule. The small 20mm will be as portable as the .50 BMG.
Even the German 7.9mm was going to need 5-7 men for a "crew" if there is no transport, either motor or hooved. The US .50 was probably closer to 9-12 men although that is just a guess as the US never moved it that way. You need at least 2 men to carry the .50 itself. You need 3-4 men to carry the mount and you need ??? men to carry the ammo, You also need one NCO to supervise
This may be a post war mount, the M63, but it weighed about 65kg.
Not all the earlier mounts were really satisfactory.
Yes you could shoot the big .50 at an airplane, if the air plane co-operated by flying slow and steady. Sitting on an ammo box while trying to aim at a fast moving aircraft was not going to work. Which means a larger, heavier, mounting system. At which point the exact size/weight of the gun itself starts to become a much smaller part of the entire system.
British Motley mounting for Brens.
usually mounted in a truck bed, single guns in France in May-June 1940.
A small 20mm will handily out-range a LMG (unless the small 20mm is firing the heavy, 120-140g shells, that we don't want to happen here), and the effect on the target will be much greater. If a trailer or a cart is worthwhile for two LMGs, it is even more worthwhile for the small 20mm. Use Kubelwagen or a similar vehicle, even a mule will do just fine - not every Army was American or British.
A lot depends on the desired range and traverse. The German 7.9mm had very close to the same time of flight to 600 meters as the German 13mm MG 131 and both were about 0.2 seconds quicker than the MGF-MM using mine shells. Using shorter/lighter shells that loose velocity quicker may not get you much unless the range is really short.
Americans insisted on the HMGs on the tanks, OTOH. Supposedly Rudel was downed more than once with these.
Seems like we agree that LMGs as AA weapons on the tanks are not that a good idea.
A big problem with tank mounted machine guns is the rather limited amount of elevation and traverse the gun actually has as opposed to the physical limits of the mount.
this website has a number of pictures that emphasis the rather optimistic expectations of several nations.
A blog about World War II era archive documents, primarily dealing with armoured warfare.
We are in misunderstanding here. I'm not trying to sell the small 20mm as being as good as the big 20mm, but to offer an alternative to a HMG or a LMG pressed into the AA role.
A lot of the problem is not the gun or ammo itself, it is just being able to hit the aircraft (or even put tracers close) given primitive sighting systems and poor elevation and traverse arrangements. It is one thing to heave around a 10-15kg gun and ammo supply, when you are dealing with even a small 20mm you are dealing with 40kg plus (drum and ammo on top of the weapon). You have to be able to use legs and the whole body.
Americans seem to have been using the HMGs a lot as the ground support weapon, from their tanks or otherwise.
Yes and the US went to the M45 quad mount
which used 4 guns to make up for the low rate of fire and used electric motors for traverse and elevation to try to keep up with fast moving aircraft.
US did put the whole mount on trailers, using batteries and generators but they did not use mules/horses to tow them
The tombstone ammo boxes hold 200 rounds each and sometimes the gunners fired the guns in pairs to both extend the firing time and to help keep the barrels cool.
The US .50 did not use HE ammo and it's incendiary was on weak side but it did have the shortest time of flight to 600-1000 meters aside from the Soviet 12.7 and the German 15mm so aiming was less of problem (not actually solved)