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Speed of exploding shell


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#26 nigelfe

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Posted 20 April 2012 - 09:02 AM

I shall talk to some of our scientists later and get you the V of D for TNT and some of the common fillings.


Just go to my web site page http://nigelef.tripod.com/ammo.htm there's a table there.

The overwhelming influence on where splinters go is angle of descent, a moment's mental modelling will reveal this.

30 yds is about effective splinter dist, basically it reflects splinter density, hence larger shells are greater, smaller less. Of course in WW1 fragmentation wasn't that great because the ratio of HE to metal was very low. Safe distance is much greater and is the dist where you could still get some large pieces of metal. The abolute distance used on firing ranges in UK is greater still and reflects heroic assumptions about how far a splinter might go.

The shrapnel distance is the effective distance from the point of 'burst'. Bethel states that for heavy field guns (ie 60-pr) this could be quarter of a mile, ordinary field guns were less. Obviously there's two factors here, bullet weight (ie carrying power) and angle of descent. Bethel also states the usual initial velocity provided by the bursting charge to the bullets was only 150 - 200 fps. The other issue about effectiveness is target posture, men lying down presented a much smaller target than those standing up.

The French used a very flat angle of descent with their 75mm because it had high velocity, Germans used a steep angle, partly because of their guns and partly doctrinal, UK was in between.

#27 truthergw

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Posted 20 April 2012 - 09:24 AM

The trajectory of the French 75 was a function of muzzle velocity and ultimately of the type and amount of propellant for a given mass of projectile. All non powered projectiles follow a parabolic path from launch to strike. As the launch speed increases, so the arc can flatten for a given range. It helps if we use standard terms. Speed is distance over time. Velocity is speed in a given direction. Acceleration is change of velocity.

Sorry Walter, a rocket from a plane will travel faster than a bomb. Speed of the rocket is added to speed of the plane. Same goes for a bullet. Imagine the pilot dropping a bullet out of the cockpit. We know it will not go as fast as one fired from his gun.

#28 31543 Ogilwy

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Posted 20 April 2012 - 10:45 AM

Nigel,

Thanks, that saves me a long conversation trying to get something simple out of a 'Boffin'. "Picrite"!! Too much work at the moment looking at picrates, I meant Picric Acid (one of my favourites, as they go with a lovely 'Crump' ).

I wonder how much fragmentation patterning they would do at the time? I would have thought that a few witness screens at the trials would be about all!

We carried out some archaeology on some trenches on one of the range areas and found that they had been made for the purpose of, I believe, testing the effectiveness of shrapnel under different distances and angles of functioning from troops in cover. For them the angle on functioning would be critical and the trench system they had created was very elaborate showing a lot of care and thought had been taken.

Ah well it's lovely when the day job and hobby are the same, but back to the grind (more 155).

Regards,
Rod

P.S. Nice website, nice to see the long range - drop shorts getting a good write up.

#29 nigelfe

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Posted 21 April 2012 - 01:24 AM

The trajectory of the French 75 was a function of muzzle velocity and ultimately of the type and amount of propellant for a given mass of projectile. All non powered projectiles follow a parabolic path from launch to strike.


Being a pedant in these matters, I have to say 'wrong'. A trajectory is only parabolic in a vacuum. Air resistance means means that it is more like an ellipse, that said an upper register/high angle trajectory (ie tangent elevation (TE) greater that about 45 degrees (it varies with different guns)), is very close to parabolic as is the other extreme of a very flat trajectory.

The angle of descent, which is important for shrapnel, steepens the closer it is to maximum range. Obviously with howitzers capable of TE close to 45 degs the shrapnel can be 'fired' by the carrier shell near to vertically downwards. However in WW1 guns seldom had a max TE above about 25 degs, hence their angle of descent was always relatively flat, not much more than the TE even at max range.

#30 nigelfe

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Posted 21 April 2012 - 01:48 AM

I wonder how much fragmentation patterning they would do at the time? I would have thought that a few witness screens at the trials would be about all!


I'm not sure that much study of HE shells was done in WW1, mainly because its quite difficult. You can do static shells, positioned to reflect an angle of descent in the open surrounded by plywood screens (this seems to be the usual modern method), or in a big water tank, where the water slows down the fragments so they don't go far but you can recover them all and hence get the size profile. The problem is that the terminal velocity influences the direction the fragments go in. That said once you got the fragment size profile and the fragment initial velocity from a static shell, got data about the effect of air resistance on fragments then you can do computer simulations. It's not until you compare pictures of the cross section of WW1 shells with modern ones that you realise how primitive it was in WW1, not forgetting that the steel was also very inferior compared to what's used today. Of course this also kept ammo production costs down, TNT was expensive compared to other explosives hence it wasn't widely used.

Until mid WW2 the old 58 ftlbs criteria is what everyone worked to, hence fragments were larger and there were fewer of them for each shell, this kept shell lethality relatively low. In WW2 guys like Solly Zuckerman RAMC did the research (using all sources of info including the casualties caused by German bombing of UK) and realised that far smaller fragments were lethal and this led to stronger steels and more explosive filling to get lots of small fragments.

#31 RodB

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Posted 21 April 2012 - 12:55 PM

That makes a good deal more sense than some of the earlier postings (including mine), because the 6000 yards the Wiki entry is based on is a pretty unrealistic range for shrapnel rounds from a gun of around 3" calibre.

Most of the field guns of the major participants had broadly similar performance to these details above, and 2 or 3,000 yards was the practical range for direct fire with shrapnel. At such distances the velocities of shrapnel balls would be in the transsonic range and energy more than a dozen times greater than at 6000.

Should've spotted that sooner! :(

Regards,
MikB

The numbers in the Wikipedia article are an attempt to show the theoretical maximum lethal range for a shrapnel bullet from a typical 75 mm / 3 inch field gun, inferring that it could be lethal up to about 6,000 yards using the 58 footpounds rule of thumb : i.e. accurate shrapnel was a potential mankiller out to a pretty long range. Obviously at the typically much shorter ranges encountered in action a hit by a bullet would be far more deadly. Please correct if the numbers are wrong.

#32 truthergw

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Posted 21 April 2012 - 02:17 PM

Being a pedant in these matters, I have to say 'wrong'. A trajectory is only parabolic in a vacuum. Air resistance means means that it is more like an ellipse, that said an upper register/high angle trajectory (ie tangent elevation (TE) greater that about 45 degrees (it varies with different guns)), is very close to parabolic as is the other extreme of a very flat trajectory.

The angle of descent, which is important for shrapnel, steepens the closer it is to maximum range. Obviously with howitzers capable of TE close to 45 degs the shrapnel can be 'fired' by the carrier shell near to vertically downwards. However in WW1 guns seldom had a max TE above about 25 degs, hence their angle of descent was always relatively flat, not much more than the TE even at max range.

When you say, " more like an ellipse", what curve does that actually describe?

#33 MikB

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Posted 21 April 2012 - 03:55 PM

The numbers in the Wikipedia article are an attempt to show the theoretical maximum lethal range for a shrapnel bullet from a typical 75 mm / 3 inch field gun, inferring that it could be lethal up to about 6,000 yards using the 58 footpounds rule of thumb : i.e. accurate shrapnel was a potential mankiller out to a pretty long range. Obviously at the typically much shorter ranges encountered in action a hit by a bullet would be far more deadly. Please correct if the numbers are wrong.


I wouldn't think of correcting the numbers - I have no independent way to measure or calculate them accurately, and in any case they agree with my expectations as a reasonably well-read and experienced amateur ballistician.

I can accept 6000 as the maximum theoretical effective range, but the OP asked a simple question that would presumably expect an answer relating to the most typical range of conditions. The 6000 yards is practically the only mention of shrapnel engagement distance in the article, and the significance of this in defeating the value of the numbers given as a 'typical' answer didn't occur to me until a lot later. It would be useful to include a statement that the 6000 yards is an extreme range and that 1500 to 3000 was very much more typical.

I realise my knowledge is limited, but I don't think I've heard of a saturation barrage being delivered at 6000 yards with guns of field calibre, and I can't imagine anything less being effective so far outside realistic spotting range for shrapnel.

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MikB

#34 gunnersdad

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Posted 21 April 2012 - 07:43 PM

This from the Army Armament Research and Development Centre Dover New Jersey

The work shows that the physical structure of TNT breaks up during burning. Combustion proceeds on fragments with a new surface to volume ratio. The size, shape, and number of fragments is determined by the crystal pattern permitted to develop by the casting procedure. The intrinsic burning rate of TNT is very slow in relation to the rate of structural dissociation.

I'm no scientist but I think we might assume from what they are saying that the resultant force of shrapnel is dependent on its surface area and the explosive pressure applied to it. Velocity is one factor but I think force is quite another.

Mal

#35 RodB

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Posted 22 April 2012 - 12:31 AM

I've added to the Wikipedia article the shrapnel bullet lethality calculation for a hypothetical average field gun bursting at 3,000 yards (shell velocity of about 900 feet/second + added bursting velocity) : comes out at 418 foot-pounds, or seven times the French and US minimum calculated energy to disable a man ! This is due to the squaring of velocity.

#36 nigelfe

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Posted 22 April 2012 - 01:29 AM

I think a trajectory is a segment of an ellipse.

Shrapnel was used at quite long range in the Boer War, the air was very clear on the Veldt, hence very good visibiity even if the binoculars weren't too good. The prospect of long range shrapnel fire was on of the reasons for the 60-pr.

The issue was that at longer ranges, even when TE was still only about 20 degrees the angle of descent increased and this reduced the length of 'beaten zone' of the bullets. It's this beaten zone length that meant the most effective range was around 3000 yards, it's nothing to do with the residual velocity and hence energy of the bullets. The longer beaten zone was most effective against men standing up (ie vertical target), the shorter zone with greater bullet density (ie more bullets per horizontal sq yard) would be more effective against prone men.

#37 CharlieBris

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Posted 22 April 2012 - 06:59 AM

Perhaps some data on WW1 guns might help:

Muzzle velocities (max. elevation)

Krupp FK 96 n.A (L/27) - 465 m/sec (+16 deg)
18 Pounder (L/27.9) - 492 m/sec (+16 deg)
Krupp 75mm M1903 (L/30) - 500 m/sec (+15 deg)
Mle 1897 (L/36) - 584 m/sec (+18 deg)
76.2mm Putilov M02 (L/30) - 588 m/sec (+17 deg)
Rheinmetall FK 16 (L/35) - 545 m/sec (+40 deg)

It was noted earlier that the field guns were used in barrages at long ranges (6000m) - it was standard practice for the FK 96 n.A to
dig the trail in to increase the elevation. In barrage fire this would be worth doing.

The FK 96 n.A barrel had a max. range around 7800m - the KiH (FK barrel and receiver in lFH 98/09 carriage) modification could reach this range.

It was suggested that the WW1 guns were fairly flat trajectory - true for the light field guns but the 10cm Feldkanones (Krupp K04/14/17, Skoda M15) could elevate to +30 deg and fire
shrapnel rounds. All the German and Austrian howitzers had shrapnel rounds available - most could elevate to +40 deg and had reasonably control over muzzle
velocities.

Regards,

Charlie

#38 MikB

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Posted 22 April 2012 - 10:23 AM

When you say, " more like an ellipse", what curve does that actually describe?


Parabola and ellipse are both symmetrical shapes, which a trajectory in atmosphere can't be because of the lower velocity of the downward component. I doubt the shape has a name, because it has no simple geometric derivation as parabola and ellipse do.

Regards,
MikB