No, not aircraft armament - that controversial debate is an area I'm not gonna touch again... I'm just wondering which is the best for use as the coaxial gun on a tank/AFV. The pros/cons seem to be: .3 - small gun, high rate of fire, wimpy little bullets that cannot pierce a lot of objects commonly used for cover by enemy infantry. .5 - larger gun, slower rate of fire, bullets that can pierce a lot of objects commonly used for cover by enemy infantry. 20mm - even larger gun, slower rate of fire, but with explosive bullets - or AP bullets, or a mixture. .3 was definately the most common in WW2, and IIRC is still the most common today. .5 seems to be more common as the Commander's AA gun, but many modern MBTs use it coaxially - like the Cheiftain. 20mm was first used in this was in the Centurion, IIRC, although it was quickly phased out. It is much less common, and the only tank I can think of that uses it is the AMX-40
There is also the issue of packing a useful number of rounds into the available space. Unlike a plane a tank probably can't ever afford to run out of ammo. I’m guessing that a tanks machine gun isn't really there to kill people it's mostly there to keep enemy infantry suppressed. A .3 round might not be that powerful but if you have them zipping around you, you will still duck. As such having lots of ammo is more important than individual hitting power.
I agree that the main use of the coaxial is infantry supression and damage so really you don't need anything particulary big. I assume most german tanks mounted MG34/42's which fired I believe standard 7.62 rifle ammo. If the infantry are hiding behind anything of substance your main gun can be brought to bear firing either HE or AP as necessery. This also applies to weak amroured vehicles like WW2 half tracks where a heavy MG would be effective but not really needed due to your main gun. Inside a tank space is a premium so smaller rnds have a big advantage as running out of coaxial when being attacked by infantry would be a major nightmare. Commander AA guns are a different matter though, here you need something reasonably big just because of the ranges involved and the need to cause significant damage to a superstructure which is possably armoured (ground attack craft) with just a few hits. Here a .50 call or similar would probably be best in mind. BTW, why is a .30 cal wimpy? Presumably it's a heavier round than the 7.62 MG42 used? FNG
In the Israeli armor I've built, I've noticed a trend towards mounting a .50 caliber M2 on the mantlet directly over and above the main-gun. I'm not sure if this was an economy measure that allowed the commander to spot a round's impact using the .50, then switch to main-gun ...or simply because turret-space was limited and it was deemed easier to mount the .50 cal BMG outside the turret. Tim
Or was it simply an 'extra' machinegun - the Israeli's experiences with RPGs have caused them to hang as many machineguns as possible on their tanks for infantry supression. This rather beautiful cutaway diagram of a Merkava Shows well the .5 can over the mantlet, plus two extra mgs associated with the 2 turret hatches. I honestly do not know if the Merkava has an internal coaxial machinegun though. However, not every Merkava has this external .5 cal mg, so I would assume it does have a 'true' coaxial, and that the .5 cal is just for additional firepower. The M60 does have coaxial mgs, and some of them also have the mantlet-mounted .5 cal.
The Merkava keeps the engine in the front with a space at the back for stores or a couple of infantry.
I* thiought the MG 42 and MG 34 used the standard rifle round teh K98 used the 7.92 X57mm Mauser, with my source having the 7.92 I beleive you are wrong. Althought I beleive the MG-3 (the modified version of MG42) was modified specifically for the NATO 7.62 round. http://world.guns.ru/machine/mg32-e.htm http://world.guns.ru/machine/mg33-e.htm http://world.guns.ru/rifle/rfl02-e.htm http://world.guns.ru/machine/mg08-e.htm the first 3 prove the support the use of 7.92 instead of 7.62 and the 4th shows evidence of 7.62 used in the MG-3
Which would in fact make the .30cal round the lighter one. But at such a small level I don't think it matters much; both these MGs are "light". I think Ebar has a good point with regards ammo. Whenever I saw a .50cal MG in a museum, the size of its rounds always impressed me; it would not be practical to take this weapon along as a coaxial because it would simply take too much space for ammo.
In wwII at least, wasn't the British .303 a heavy bullet? And so the Besa tank MG, with a high rate of fire (750+ ?) would be quite a hail of gunfire. Still, in NW Europe, I would prefer the U.S. .50 MG, as the German soldiers "feared" it. Sometimes they replaced the .30 on top of light tanks with these as added firepower, and have seen them welded onto scout cars etc. As Churchill tanks have been described as "roomy", I like the idea of the aforementioned .50 in the hull MG position for extra assault power
RE: .3 vs.5 vs 20mm I think that the .5 is the best because it's somewhat a combo of the 20mm and the.3. It has a reasonable fire rate and a satisfactory penetration ablility. Plus it was the armament of the P-51 Mustang, one of the greatest WWII fighter planes. I'll just say the P-51 didn't get that good without good armament. Plus, both the .3 and the 20mm were somewhat unused by the US, and they did great in WWII.
Re: RE: .3 vs.5 vs 20mm I agree with you that .50 is probably best of those for coaxial gun. .30 is doable but 20mm is overkill. And by the way, I believe that great majority of shots fired by US military forces during WWII were .30 cal. Also 20mm AA-guns were used by USN and 20mm aircraft guns (Hispano's) were produced by US for US aircrafts in great numbers. Unfortunatelly they screwed up and produced faulty copy of original guns.
The .303 did fire a heavier bullet than most .30 cal or 7.92mm loadings, but not by enough to matter. The Besa was used in 7.92mm anyway. Incidentally, the metric designations (calibre and case length in millimetres) for the various rounds are: 7.92 x 57 .30 = 7.62 x 63 .303 = 7.7 x 56R .50 = 12.7 x 99 20mm = 20 x 110 The Allied troops also feared the MG 42, because of the 'tearing' noise of its high rate of fire. Tank MGs were basically for dealing with personnel - they had a bigger gun for vehicles - and the rifle-calibre MGs are adequate for that. Furthermore, tank MG fire was often just for general suppression rather than aimed at anyone in particular, so they got through a vast amount of ammo. Given the restricted amount of storage in a tank, the size of the ammo really mattered - which is why everyone (except the French) still use 7.62mm co-axial guns in tanks to this day. Tony Williams: Military gun and ammunition website and discussion forum
In essence the mg on a tank* is only a supporting act. The big gun is the main event. *ignoring the little mg only toy tanks
