Mk 108 30mm

[Apeking]

This is more of a real-life question than something to do with Aces High, and I imagine Tony Williams can answer it at the drop of a hat. I have been reading about the Mk 108 30mm cannon which is fitted in some of the late-war German planes. It's a fascinating thing and it has given me a great deal of pleasure in Aces High, but it has also caused me a great deal of pain, because it has led me astray, taunted me, placed me in danger and left me to die. As a work of art it looks wonderfully modern even today:
Mk 108 at Luft '46

Really I have three questions. Firstly, why was the barrel so short? I assume there was a good practical reason - perhaps the shells could not withstand a higher muzzle velocity, or the gun could not function with a long barrel - but I have not yet heard it. From what I have read (on Tony Williams' own site!) it was a more compact revision of the earlier Mk 101, but it looks as if the designers threw out the baby with the bathwater by shortening the barrel so much.

Secondly, contemplate this fascinating cut-away of a 109 K4's weapon installation:
A faceless K4

The Mk 108 spinner cannon looks comical; it barely enters the engine block. What bridged the gap between the cannon muzzle and the prop spinner? A plain metal tube (if only to prevent the muzzle blast from damaging the engine), or nothing at all, and if the former did it have an effect on the weapon's muzzle velocity?

And straying off topic, I have read that the Germans considered using the MK 108 as a ground-based anti-aircraft gun, because they had lots of them and they were easy to make. They seem very unsuited for this role, but on the other hand they are similar to modern-day 40mm grenade launchers. Did anyone think to put one in a light tank, or jeep? With the right shells it would be a potent anti-personnel, anti-light structures weapon.

[Tony Williams]

One correction to your post - the MK 108 was not derived from the MK 101, which used an entirely different mechanism. It would be more accurate to describe it as a scaled-up MG-FF.

The barrel was short partly because the cartridges contained very little propellant, which burned out after the projectile had only travelled a short distance up the barrel. The more propellant you have, the longer the barrel you need to get the most out of it. In the photo below you can see the huge different in size between the cartridges for the high-velocity MK 101/103 (30x184B) and the low-velocity MK 108 (30x90RB)



Another reason for the barrel being as short as it was concerned the type of operating mechanism. The breech was not locked to the barrel at any time - when the gun fired, the breechblock was moving forwards, and the recoil first stopped it then pushed it back again. The shell had to be clear of the barrel before the cartridge case left the chamber, otherwise the case would burst and the plane's structure around the breech would be blasted with burning propellant. So the barrel had to be kept short to ensure that this did not happen. There is an obvious relationship here between rate of fire and barrel length: a heavier breechblock would move more slowly, giving more time for the shell to leave the barrel, so the barrel could be longer, but the Luftwaffe put rate of fire above muzzle velocity in their priority order for this gun.

As for your second question, there was a blast tube attached to the muzzle which ran between the engine blocks and up to the prop, otherwise the engine compartment would have been filled with gasses and soot from the muzzle blast. It didn't affect the velocity.

The Germans were in such desperate straits at the end of the war that they might well have considered using the MK 108 in the AA role, I don't know, but they would have made very bad AA guns - you need high velocity for that role. I agree that they could have made useful infantry weapons, but I don't know that that occured to anyone.

Tony Williams: Military gun and ammunition website and discussion forum

[Apeking]

A typically a well-written and informative answer. So the Mk 108 was basically a blowback gun along the lines of a Walther PPK or other compact pistols, but scaled up? And with a much bigger kaboom. It seems like one of those nearly-there-but-not-quite solutions, or a solution in search of a problem.

If the problem was a bursting cartridge case, could the designers have made the breech-face so that it wrapped around the end of the cartridge, along the lines of the telescoping bolts used in some modern submachineguns? I can't picture in my mind how the cartridges would have been ejected in this case.

I was struck by the 30mm cannon because my dad used to test cannon shells for the RAF, and brought home a dummy 30mm Aden round one day. I remember wondering what one of those things would do to you, if it hit you at supersonic speeds, even if it did not explode.

[Benny Moore]

Another interesting thing is that German aces universally disliked the three centimeter cannon, considering it unfit for destroying fighters.  According to one of the aces, all it usually did was knock off skin.  Add that to the terrible ballistics and relatively poor rate of fire, and it's no wonder they did not like it.

[zorstorer]

Tony I have an odd question kind of related to this....

How much did necking down the brass effect the muzzle velocity?  Just wondering what sort of gains and draw back the necking down has.


Apeking, when I was still in the Army as a Bradley gunner my bradley commander was in the first desert storm.  Long story short the gunner in his bradley still had AP loaded when they came upon a group of iraqis who wanted to fight, well the gunner selected HE but you still need to cycle the ready round out of the gun or just fire it....well he decided to fire it.  After the fight they found the guy he hit with the AP round...he was missing the left side of his chest from shoulder to hip.  So just getting a chunk of metal going at 3600 ft/sec is going to be deadly.  Plus that round after the sabot falls of is only about the diameter of a number 2 pencil and about as long as your pinky.

[Benny Moore]

How would one know whether a particular corpse was killed by high explosive or armor piercing bullets, if they both do such spectacular damage?

[zorstorer]

Well with the optics in the bradley, its not too hard to put the pipper on 1 man at 1000m and hit him.  Plus after you fire off the "ready" round you need to cycle the gun for the next type of round.  So its not like firing off a machine gun.  Take it or leave it I trust the guy but it's up to you.  Try doing up the math on the kenetic energy of the 3.39g projectile going at around 4500 fps.  

If I did it right it comes out to around 3000 Joules.

Also a .45 ACP has about 543 Joules.

Plus it wasn't a large scale engagement, more like a skirmish.  Sounded like a few guys standing around with weapons in the path of some nasty hardware.

[Debonair]

Originally posted by Benny Moore
Another interesting thing is that German aces universally disliked the three centimeter cannon, considering it unfit for destroying fighters.  According to one of the aces, all it usually did was knock off skin.  Add that to the terrible ballistics and relatively poor rate of fire, and it's no wonder they did not like it.

A few months ago i read a book by an east front 109 pilot who loved the 3cm gun
one hit would drop just about any plane, he said...

[GRUNHERZ]

MK108 is awesome in AH and apprently in real life. Here is what one round did in a post war british test.

[1K3]

MK 108 should be a perk weapon for ToD:aok

[Krusty]

No more than the 20mms on the spitfire should be. They have more of them, they are 90% more likely to hit the target, and more lethal in most cases when fired at the enemy. Both were the norm, why perk either?

EDIT: depending on when the tour starts, you may have to fly the G6 in the beginning, or the 190A5. You will probably advance up the ranks to the G14 (30mm) or the 190a8 (30mm) so at first it probably won't be available

[Reynolds]

Originally posted by 1K3
MK 108 should be a perk weapon for ToD:aok

Do you know how few people can actually AIM it? I have practiced for AGES (I favour the 30mm over all others because of those few incidences where one shot ripped off important things like engines, wings or... tail sections ) and I have a dreadful hit percentage!

Quick question: OUR G-14 has the Mk 108, correct? (From what ive seen the 101 seems more my type of gun)

[1K3]

Sry for misunderstanding.


IF 1 round of MK 108 did this to a plane then it must be perked

[Lusche]

Originally posted by 1K3
Sry for misunderstanding.


IF 1 round of MK 108 did this to a plane then it must be perked
 

I´m with Krusty this time: no need to perk. The lethality of a single round is being offset by the increased difficulty of actually achieving a hit.

[Tony Williams]

Originally posted by Apeking
If the problem was a bursting cartridge case, could the designers have made the breech-face so that it wrapped around the end of the cartridge, along the lines of the telescoping bolts used in some modern submachineguns? I can't picture in my mind how the cartridges would have been ejected in this case.

The MK 108 was an "Advanced Primer Ignition Blowback", which was a lot more sophisticated than a simple blowback pistol, because the breechblock was still moving forward at high speed when the cartridge fired. This meant that the initial recoil thrust was mostly used up in stopping the breechblock before it could be pushed back again - which meant that the breechblock could be a small fraction of the weight it would have to be in a simple blowback, where the breechblock is stationary at the moment of firing. A much lighter breechblock means a much higher rate of fire. In fact, a simple blowback wouldn't work at all in cannon calibres - the breechblock would have to be so heavy that if the gun were pointed upwards, it would slide back by itself since the spring wouldn't be strong enough to hold it.

In order to provide support for the cartridge case while it is being fired, API blowbacks have extended chambers, so unlike all other guns (where the chamber is a close fit around the cartridge) the cartridge is free to slide to and fro. Since the breechblock needs to be linked to the cartridge case by the extractor claw, that means the breechblock needs to be the same diameter as the cartridge case so it can follow the cartridge into the chamber. Normally this would be impossible because the extractor claw, fitting around the rim, would stick out from the case, but cartridge cases for API blowbacks are specially designed with rebated rims - the rims are smaller than the case - to allow this to happen. You can see the small rim in the pic of the 30x90RB above.

The API Blowback was first introduced in the German 20mm Becker cannon of WW1, then taken up by a couple of Swiss firms; first SEMAG, then Oerlikon, who made 20mm cannon in various versions. The most powerful Oerlikons were adopted by the British and US navies in WW2 as light AA guns, the less powerful ones adopted by the Japanese navy as aircraft guns (Type 99 cannon, as used in the Zero) and by the Luftwaffe, who called it the MG-FF. You can read a brief history of the Oerlikon family HERE

Tony Williams: Military gun and ammunition website and discussion forum