Malcolm McKayIncidentally, 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 –
Malcolm McKaySlow 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.
Malcolm McKayInteresting 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
Malcolm McKayBTW, 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. 😉
Malcolm McKayAn incendiary round really just has a dob of phosphorous in it – there is little explosive effect and certainly nothing that would match the damage created by a 20mm explosive projectile.
https://sites.google.com/site/britmilammo/-303-inch/-303-inch-incendiary
Malcolm McKayYes, but the problem is not entirely related to the size of the projectile alone. .50 cal. ammunition is just an enlarged rifle calibre projectile in real terms.
When a projectile leaves the muzzle its velocity starts to fall and as that does gravity takes over, plus the important matter of drag as the projectile moves through the atmosphere. At relatively close ranges of 600 yards or less there is still enough speed in the projectile combined with its mass to do damage, however atmospheric drag has to be factored in as does the fact that the burst of projectiles are all not going to arrive on the target at the same time or in a compact mass. That being due to the trajectories of both aircraft plus the trajectory of the machine guns of the attacking aircraft. Accordingly, and unless the target aircraft is unlucky enough to be both close enough and in a position to receive the full burst of fire, perhaps only a fraction of the fired projectiles will impact on a suitably vulnerable part of the target.
So despite the increased calibre and the exponential growth in the mass of the projectiles one is still dealing with the problem of getting a kill from inert ammunition behaving in a sprayed fashion. Now that’s where explosive ammunition e.g. 20mm cannon ammunition increases the odds quite markedly because if a hit is achieved then not only is a hole punched in the target but the resulting explosion creates greater structural damage than an inert round could. The limit on the cannon ammunition of the period was still the rate of fire which was why the US retained the now semi-obsolete .50 calibre until missile and rocket volley armament was developed and later combined that with the Vulcan rotary gun which finally increased the rate of fire of cannon armament beyond that offered by the conventional automatic weapons. The RAF went the other way and combined 20mm and 30mm cannon armament with air to air missiles. Both options are effective.
As a footnote I might add that a gun like the Vulcan is not a conventional automatic weapon and should not be confused with such because its firing sequence is not activated by the harnessed gas of a round, but by an electric motor which drives a purely mechanical rapid fire system that was first developed by Gatling way back in the 1860s. Of all the rapid fire small arms it is perhaps the most effective and depending on the magazine capacity will lay down a prodigious rate of fire.
Malcolm McKayBeautifully done.
Malcolm McKayQuestion I am chasing is, can a .303 cause a hole about the same size as a 20mm?
Not really – a .303 projectile is just .30 of an inch in diameter while a 20 mm projectile is approx .78 of an inch in diameter, and being an explosive projectile would create a large jagged exit hole and if it exploded on contact would create a large jagged entry hole. The .303 might make a larger entry hole if –
1. It had tumbled in flight and keyholed (i.e. hit at an angle) the target, or
2. had been deformed after hitting the target and you were looking at the exit hole.
HTH
Malcolm McKayThe added effect of hollow point/soft nose/dum-dum pullets on stopping power is all very well but such ammunition is banned from military use by the Geneva convention.
As a man stopper rounds in the 7-8mm range are very effective. If you are close enough to the firer and hit in the chest the round will leave a neat entry hole but take half your back away as it exits. Definitely not nice.
Indeed, but in general I have always thought that getting shot would stop me anyway. 😀
The internal damage to which you refer is a result of the shock wave being transmitted through the body, although this exit wound effect is better seen where a body is moving through the areas of larger body mass. Head, or chest for instance.
In the 19th century when smaller calibre pistols became popular due to the revolver replacing the single-shot pistol (large calibre revolvers in short .577 were made however the pistol was huge, heavy and unwieldy) it was found that black-powder (gun powder) propellants lacked the necessary power to make pointed projectiles as used in .31, .36 and .44 revolvers effective man stoppers despite what Hollywood claims. The introduction of smokeless powders which upped the power by a factor of five turned these previously relatively ineffective calibres into highly effective ,32, .38, 9mm and .45. and the British also began using large flat nosed .455 projectiles in pistols which were deadly at the close ranges at which pistols are used.
That aside, another reason for dropping flat nosed rounds is that in rifles which are designed to have far greater ranges than pistols, a pointed or aerodynamically shaped round incurs far less drag and thus, because as we are aware the projectile’s maximum velocity decreases the moment it leaves the barrel, it is able to carry for much longer distances before losing speed and accuracy. The fact that being hit by such an aerodynamically efficient round makes for a less horrendous wound than a blunt nosed projectile was, I suspect, rather secondary in the military mind to the benefits of greater range and accuracy. Shrapnel produces far worse damage than any flat-nosed or large ball type ammunition ever would either in people or in machines. 😮
Exploding projectiles in military infantry small arms were introduced in the 19th century but the horrendous wounds these produced as noted in the US Civil War quickly caused these to be banned. We now use these in automatic cannon type weapons but ostensibly against inanimate targets rather than people – although on the battlefield no projectile is capable of discriminating.
Malcolm McKayIt’s a combination of two things.
1. The shock cone generated by the projectile as it moves forward, and
2. the shock wave generated by the explosion of the shell.
An ordinary nonexplosive projectile generates the same forward shock wave which is what causes the major damage to tissue if it strikes a body. As I posted earlier that is why soft nosed expanding projectiles are favoured as man stoppers. They are not so effective on aluminium structures because the void spaces therein don’t provide a sufficient medium by which the shock wave can be transmitted.
Malcolm McKayOf interest, and as a follow on to Graham’s post, in the Korean War the USAF found that the armor plate fitted to Mig 15s was pretty much impervious to the 0.5 inch ammunition used by F86s. Trials were carried out in which the 6 x 0.5 inch were replaced by 4 x 20mm cannons and these proved adequate for the task – however at the time given the aerial supremacy enjoyed by the USAF there was no push for a changeover.
But to come back to 7mm ammunition (or in its variants like .30 or .303 inch) it all depends upon where the target is hit as much as rate of fire. One projectile hitting a pilot is sufficient, or one or two projectiles hitting the pipes of the cooling system of a liquid cooled engine is sufficient. These may be freak shots but they accounted for many kills. The notion of weight of fire in the early 1930s was a product of the lack of suitable automatic explosive projectile weapons (AKA cannon) which were of the appropriate light weight and rate of fire that could be fitted to fighters engaged in high speed combat. It was only in the late 1930s that such weapons became available and as we know were successfully trialed both in the opening months of the Battle of France and in the Battle of Britain.
The German cannon had a rather slow rate of fire which led to the retention of mixed MG and cannon armaments while it is not really until the RAF introduced the Typhoon that we see an all cannon armed aircraft – 20mm being the preferred type. I won’t go into the rate of fire problem because it is rather long winded. However eight or twelve .303 inch MGs (as fitted in Hurricanes and early Typhoons) can put down a devastating weight of fire on a target which is equaled by the explosive projectiles of 4 X 20mm cannon. But the cannon has the added benefit in that a few hits by the explosive shell is more effective than a similar number from the ordinary nonexplosive .303 inch projectile.
Malcolm McKayIt is no where near 10,000 rpm per second, the barrel twist is 1 in 12, meaning 1 revolution in 12 inches in travel.
As far as how effective, not very, that is why the Hurricane had so many guns. The 303 is a great round against troops, but it is too light for use against aircraft. The US 50 caliber was more effective because of the diameter and weight of the bullet.
During the Boer War the British Army carried out long range accuracy testing of the Lee-Enfield rifle which fired .303 ammunition. The maximum distance was about four miles. While accurate shooting relying on eye sight was naturally impossible at that range they were still found to be able to drop projectiles into a relatively small area. This was of the sort of nuisance value designed to keep an enemy’s head down though fatalities were not expected. The rifling was sufficient for that purpose.
That is an aside – you are correct in pointing out the rate of spin of the projectile. The technical problem is that the spin induced by the rifling has to be achieved without the projectile moving so fast that it simply goes up the bore having its outer layers stripped off by the rifling because the velocity has overcome the necessary attribute that the projectile has to be gripped by the rifling to achieve the stabilizing spin.
Too fast a velocity and the projectile’s outer layers are melted by the friction and the core that is left achieves no more accuracy than a ball fired by a smooth bore musket. Obviously the addition of hardened jackets to the projectile and also the forcing of the slightly over diameter projectile into the bore by the forcing cone ameliorate the problem of stripping but it is a fine balance.
Malcolm McKayAnywhere between a neat hole approx. 7 mm in diameter to a ragged elongated hole if it is tumbling (usually towards the end of its trajectory). Exit hole size depends upon whether the projectile deformed after contact. If the projectile is a jacketed military round then in flesh the entry point will close up but transmission of shock waves will add to the size of the exit hole if any, but in aluminium or other thin metal sheet the exit hole will depend upon any deformation of the projectile as it passes through the structure.
Also if the projectile strikes at an angle due to the relative positions of the shooter and the target then the entry hole will be elongated according to the angle of entry. Soft nosed projectiles deform on impact causing larger entry holes and often will disintegrate while transiting through the target causing greater internal damage. That is why soft nosed rounds are favoured as man stoppers – all the energy is transmitted to the target rather than only part if the round is designed to pass through causing disablement.
Malcolm McKayNo doubt they will be buried under the main runway just out of reach at Izmir International Airport…….
:applause:
Malcolm McKayUnified Equipment Terminology?
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