What kind of damage can a 7.x mm round do?

Basically AA shells use the effect of a small amount of explosive contained in a frangible case to do the damage – against soft targets like aircraft you don’t need much metal to create catastrophic damage. That also is how most explosive projectiles and air dropped bombs work (expect for the thin case blast bombs e.g. cookies and their related cousins still in use). A small charge is contained in a hardened case and exploded either by a timed fuse, proximity fuse or an impact fuse.

Without seeming or intending to state the obvious, in most cases the resulting irregularly shaped chunks of steel are what cause irregular holes (of course similarly a cannon shell exploding on contact will also create these types of holes – but smaller). In the two pics I suspect that the torn hole in the second is a result of AA – could be wrong. The hole in the prop blade looks like a bullet hole – the slightly distended shape may be due to the bullet hitting a rotating blade – again I could be wrong and without being able to see it I wouldn’t really go beyond that guess.

I understand that early in WW2 a common British anti-aircraft gun was the QF 3 inch 20 cwt. During WW1 its standard anti-aircraft shell is reported to be this;-

http://en.wikipedia.org/wiki/File:QF3inchShrapnelCartridgeMkI.jpg

but I’m not sure if this was still in use in WW2. It would make sense if it was.

Ultimately the denser the fragment cloud, the higher the probability some will impact the target. Pre grooved fragmentation shells don’t actually shatter into uniform sized pieces in quite the way most people think, in reality they shed a range of different size chunks. Even if the casing is pre grooved making the warhead metal thicker reduces actually reduces the number of fragments and hence the density of the fragment cloud. So to achieve a max density and uniform sized fragment cloud you need to revert to the old fashion canister method.

Modern missile fragmentation warheads, such as the Russian BUK, use a new take on this by using thousands of individual cubes, stacked one cube thick in between two thin metal skins the inner of which contains the explosive charge.

Ground based Ack-Ack – even if not 20mm did the higher calibre guns use cannister shot with 20mm balls?

Basically AA shells use the effect of a small amount of explosive contained in a frangible case to do the damage – against soft targets like aircraft you don’t need much metal to create catastrophic damage. That also is how most explosive projectiles and air dropped bombs work (expect for the thin case blast bombs e.g. cookies and their related cousins still in use). A small charge is contained in a hardened case and exploded either by a timed fuse, proximity fuse or an impact fuse.

Without seeming or intending to state the obvious, in most cases the resulting irregularly shaped chunks of steel are what cause irregular holes (of course similarly a cannon shell exploding on contact will also create these types of holes – but smaller). In the two pics I suspect that the torn hole in the second is a result of AA – could be wrong. The hole in the prop blade looks like a bullet hole – the slightly distended shape may be due to the bullet hitting a rotating blade – again I could be wrong and without being able to see it I wouldn’t really go beyond that guess.

The hole in the channel 17 prop is considerably bigger. I can’t believe it was caused by a tumbling 303 or secondary debris. I was tempted to insert my finger into the Dornier prop by way of scale. I didn’t.

Could the hole in the propeller blade have been enlarged by corrosion over the years on the seabed? The German aluminium alloy propeller blades that I have seen seem particularly susceptible to even freshwater corrosion; would they have had a protective coating that the bullet penetration would have negated, thus increasing ‘local’ corrosion rates?

The Bf110 penetration is extremely interesting as the ’rounder’ portion of the hole exhibits a classic failure of the material in ‘shear’. The theory goes something like this: the bullet doesn’t initially penetrate the (relatively) thick aluminium plate but the (weak) bullet point deforms against it causing a small bulge in the plate; as the heavier remainder of the lead bullet deforms itself into this bulge (thus enlarging it) the edges of the bulge fail in shear and a ‘scab’ of bulged aluminium is carried through the plate by the ‘pancaked’ lead bullet behind it.

As I understand it one problem with the early armor plating was scabbing or spalling…

To this day the 120mm main guns of British tanks use something called a HESH round; High Explosive Squash Head. This is a (relatively) low-velocity round that relies on exactly this scabbing or spalling effect. It is thin-cased at the head, contains a large charge of high-explosive, and is thicker at the base where the impact fuse is located. It is designed to ‘pancake’ itself onto the armour of the target, then explode, causing large high-velocity scabs to break-off inside the target destroying the interior of the target and the unfortunate crew alike. It is very effective, irrespective of range or the thickness of the target’s armour and usefully (due to limited ammunition stowage in a tank) doubles as a high-explosive or anti-personnel round.

The armour of early tanks was hot-rolled and ‘face hardened’ rather than true ‘homogenous’ plate I believe and particularly susceptible to spalling; this was known and the tank crews were equipped with special helmets that incorporated ‘goggles’ and a chainmail face covering; probably the last time British soldiers used chainmail protection!

Those are some interesting links to the 303 armour-piercing rounds. And the penetration figures: 8mm at 175 yards are pretty respectable!

I knew that armour-piercing rounds were available in small quantities on both sides of the trenches for penetrating steel sniper ‘loopholes’ and damaging the mechanisms of enemy machine-guns (as a shot gunner coud easily be replaced) but didn’t know that the ‘reversed bullet’ technique was anything but an unofficial ‘field modification’ and didn’t know that it involved (unwisely) increasing the propellant load!

Interesting thread, but so far the assumption is the hole came from something fired by a British aircraft.

The was a lots of high velocity steel in the air from other sources; –
Ground based Ack-Ack – even if not 20mm did the higher calibre guns use cannister shot with 20mm balls?

And

Me 109 , either blue on blue mistaken identity or shots taken against a genuine target with the German aircraft being in the line of sight background.

Incidentally, in World War One, when the British introduced the first tanks, it was said that ordinary rifle bullets proved more effective against their armour if they were turned round in their cartridges and fired ‘backwards’!

As I understand it one problem with the early armor plating was scabbing or spalling (at our tank museum there are targets displayed which show this effect). When a projectile hits hardened metal its impact force is transmitted as a pressure wave through the metal ahead of the projectile, so even if the projectile didn’t fully penetrate the force transmitted through the metal is dissipated by causing flaking of the interior surface. These scabs or spalls were thrown off at velocities sufficient to cause wounds and, if large enough, fatalities. Thus even if penetration was not achieved there is still the possibility that the crew or the mechanics of the tank would be disabled. Also the plate on the these early tanks was thin by any standard simply because of the weight factor. BTW spalling still is a problem.

The Germans first tried the idea of a reversed projectile but found that reversing a projectile is not recommended as it can play havoc with breech pressures –

http://en.wikipedia.org/wiki/Reversed_bullet

and in any case a standard pointed projectile would flatten on impact with the metal surface. The British has armor piercing .303 by 1914 –

https://sites.google.com/site/britmilammo/-303-inch/-303-inch-armour-piercing

as did the Germans later –

http://en.wikipedia.org/wiki/K_bullet

I’ve not read all the threads religously, but did visit the Dornier on the open week. I have a Me110 fragment with a .303 hole through it. The hole in the channel 17 prop is considerably bigger. I can’t believe it was caused by a tumbling 303 or secondary debris. The skin fragment is on a 10mm grid. I was tempted to insert my finger into the Dornier prop by way of scale. I didn’t.

Have to agree Malcolm, getting shot doesn’t seem to be a sensible pastime. Too much chance of it being terminal.

Slow rates of fire are caused by a simple but difficult physical thing to fix. That is the length of the complete cartridge.

As the bolt cycles through the automatic fire sequence (assuming firing from an open bolt position, as in pre-cocked aircraft type guns) it is released, driven forward by the spring, and picks up a cartridge from the feed, this pushed into the breech and the pin contacts the primer, fires the round, then some of the expelled gas is bled off to throw the bolt back whereupon it reaches the end of its rearward travel then repeats the action. The distance it must travel is determined by the length of the cartridge it has to pick up during its forward travel, so as a .50 cal cartridge is longer than a .303 and a 20mm is much longer than a .303 or .50 cal; and the 30mm is longer again then the distance the bolt must travel increases as does the time taken for each firing cycle in each type of weapon.

Combine that with the speed of the aircraft involved during the maneuvers in combat and it can be seen that as the cartridge size increases the time taken for the firing sequence becomes of crucial importance. In other words you get a greater chance of hitting something with the smaller cartridge but this is achieved at the cost of damage to the target. Hence we see in the MkII Hurricane and the early Typhoons 12 x 303 mgs used while the firing rate and feed problems of the early 20mm cannons were overcome.

As mentioned in the previous post the size of the cartridge is also an issue in the number of rounds that can be carried. For those familiar with the cartridges involved I have no need to point out how much bigger the .50 cal. is compared with a .303 and how minuscule it is in comparison with the 20mm and 30mm cartridges (not to mention the size of the weapon itself). So that limits the amount of ammunition that can be carried and when coupled with the cycling speed issues then the problem is quite complex when the whole system is depending upon that brief moment in the gun sight as the human operator attempts to hit the target.

I think that comment comes under the heading of ‘No sh*t Sherlock’

In fact I wouldn’t be at all surprised if a 20mm cannon wasn’t more effective than a 50cal for similar reasons.

Moggy

As I’ve always understood it, the 20mm cannon was much more effective than the. 50. The draw back being the reduced rate of fire and ammo capacity.

And our 20mm cannons were supposed to have been a more effective ‘air to air’ weapon than the 30mm cannons in the Me 262, which was hindered by a slow rate of fire. One can only imagine the damage a quick burst of 4x 30mm cannons would have on a lumbering heavy bomber.

Most bullets, such as 303, 50cal, 5.56mm, would rather ‘fly’ backwards anyway; the spin imparted by rifling not only improves accuracy but also prevents (in air) the bullet turning round and flying the ‘right’ way. In other mediums, water, ballistic-gel, human beings, bullets ‘tumble’ and often break-up, massively increasing the transfer of energy (and massively increasing the wound in a human being).

Incidentally, in World War One, when the British introduced the first tanks, it was said that ordinary rifle bullets proved more effective against their armour if they were turned round in their cartridges and fired ‘backwards’!

Interesting questions Geoff.

I raised the matter of deformation or tumbling after entry as a way of trying to explain how the exit point of an inert round like a 7mm (or .303, or for that matter .50) could be a ragged hole larger than its entry point. For those conditions to occur then the projectile is being influenced by many variables which one can’t predict in the act of firing.

But one thing to be aware of is that if a slender pointed projectile of this type hits the surface at a shallow angle it can ricochet off. I’ve seen this happen with .303 fired at a shallow angle at water, and it is noted that even fragile materials like glass can under those circumstances cause a projectile travelling at high speed to ricochet as can thin metal. An even smaller projectile the 5.56 used in the M16 had problems being easily deflected under certain conditions by grass etc. That was why the heavier and slower 7.62 round is a preferred type still.

Of interest in the photo of the Do17 posted above is not only the clear depiction of angled entry holes but also the fact that the bullet strike has caused the metal panel to flex causing the paint to flake off. I would imagine that if that flaking is occurring then there are resonances being set up when the spinning projectile transmits some of that to the panel surface. How that would then affect the trajectory of the projectile after entry I have no idea but it could be an influence.

Malcolm

….. even an inert solid round such as a .303 may cause a larger exit hole if it is deformed by the impact or tumbles after entry. ……

Malcolm,
I’ve been pondering the tumbling aspect of the bullet inside the airframe, and its ability to do more damage on the way out. There’s a few too many parameters for me to get my mind over it. Let me think out aloud:
– close range high deflection attack: on an unarmoured airframe, the 0.303-inch bullet goes in one side, and the impact energy if reasonably high, so it goes out the other side of the aircraft. Unless it hits something more substantial – fuselage rib, wing spar, etc – in which case it lodges. It would tend to lose its energy quite quickly if it hit anything and started tumbling. Would it have enough energy to punch out the other side of the aircraft?
– close range stern/tail-chase attack: small tear entry hole, if enough energy then slightly larger tear exit hole. If it bounces off some framework inside the fuselage to strike the fuselage at 45-90-ish degrees on the way out, would it have enough energy to punch a way out?
– problem becomes more difficult for bullet exit at medium and long range because of the reduced amount of bullet energy at impact.

Regards,
…geoff

BTW, I’m not sure of the relevance of bullet man-stopping potential when compared with the potential to damage aircraft. After all, there’s no “body fluid” in most parts of an aircraft to transmit the shock wave in generating the large “exit wound”. With aircraft airframe construction you would expect a slightly larger exit hole where the structure was thinner (e.g. wings, tails, slender fighter rear fuselages – or a Do17), but mostly I would expect a entry hole size based on non-explosive bullet strike angles/range/impact energy and the bullet to be rattling around inside the airframe.

Very interesting thread,
…geoff

Oh I agree – only tangential reference in that I was alluding to precisely the point that you make make which is that an airframe consists of many void spaces. However even an inert solid round such as a .303 may cause a larger exit hole if it is deformed by the impact or tumbles after entry. But as many aircraft kills came from injury to the pilot then the effect of the ammunition type used has some relevance.

I also agree that the USAF tests in Korea with cannon are an interesting topic in themselves and your point about the harmonization (and concentration of fire achievable with nose mounted 6 X .50s) is important, especially as the Meteor which lacked the overall performance necessary to take on the Mig 15s also has a similar arrangement for its 4 X 20mm cannon.

The point you add about the increasing performance of aircraft is apposite because by Korea aircraft speed was clearly showing that WW2 gunnery experience was no longer effective in these combat situations. And you are right this is an interesting discussion because fighter aircraft, no matter what the vintage, are simply the machinery by which air to air weapons are bought to bear on the enemy. All the stellar performance in the world becomes irrelevent if the vehicle can’t be relied on to hit the side of a barn door at 10 paces. 😉

No details on the image itself…

Looks like one of the nine Do17 that attacked Kenley on 18th August 1940 (‘the hardest day’) and which got badly mauled by (303 armed) RAF fighters; a surprising number made it back across the channel to crash-land in France (thanks to their air-cooled radial engines)!

In an ideal world you do not want to kill the enemy simply wound him….

Indeed. If the balloon had gone up then we woud have been inundated with vast amounts of blister agents instead of nerve agents.

Would be interesting to see the underside, at a guess it’s a mix of cannon and .303’s.

This image was posted on another site, note the size of some holes (and that pair of .303 also)
No details on the image itself.

[ATTACH=CONFIG]233874[/ATTACH]

The latter He-111 photo shows some monstrous holes in it…

…the holes are huge and look round, but the angle is from behind, could it be torn?

Do not rule-out some other factors that could be responsible for the apparent damage; multiple, almost simultaneous, strikes by 303 rounds, for example?

There could also be post-crash factors responsible for the apparent damage. Could the existing bullet-holes have been enlarged so that they would show-up in photographs that were released for propaganda purposes?

In one case discussed on this forum the bullet-holes in a recently shot-down Luftwaffe aircraft were cut from the airframe with tin-snips by the RAF guard-detail and sold to the locals as souvenirs!

Wounded, he ties up 3 or more people looking after him, sufficient wounded and it all grinds to a halt.

which is ermmmmm tying up second line troops that cannot be first line troops because of it.