Devices

[el cid again]

Doing a line by line study of the device file prepratory to issuing RHS,
I found the usual pattern of sloppy data. Vehicles have too much - or too little - armor. Guns have too much, or too little, penetration - sometimes NONE (or 2mm!) - and do not always have anti-armor or anti-soft values - or the effect values are not equal to shell weight as they should be. In the hope of better performance during combat calculations, I have endevored to correct the data. I used the Greenhill Armored Fighting Vehicle Databook for AFVs - since it is a consistent source for all - and a set of artillery tables for all nations of WWII - for the same reason. I decided to make the anti-soft value of a shell the square root of its weight (or "effect") - due to the inverse square law - unless the gun has no HE round - as with the British 15 inch guns at Singapore - where I use the cube root. [A 15 inch shell will kill anything it hits, but it won't explode in conditions near Singapore - it penetrates far into the earth and either does not explode or its effect is shielded]. I used 1.75 times caliber for high velocity guns penetration value at point blank range - which turns out to either be what WITP used or the measured data is very close. I used half this for howitzers and even less in some special cases. I left the problem of the 12 inch CD mortar unaddressed - it might be addressed by code though.

[mlees]

Hmmm. I have seen these debates, especially in regards to Sherman/Tiger debates. The 75mm tank gun: in the orignal short barreled version, it has very poor penetration purpose. When that same shell is fired in the long barreled version, it does much better.

Both the PzKW IV and the Sherman M4, were been built with a short barreled 75mm for anti Infantry work. Both were upgunned when the tanks were called upon to shoot up enemy tanks. (PzKW IVF2, for example. The Shermans upgraded to the long barreled 75 and 76mm guns, but did not change the model designation... sigh.)

Basically, the longer the barrel, the longer the range and the better it's penetrating power. This also pertains to naval guns. (There are several calibres of the 5 inch weapon, for example.)

[el cid again]

Both the PzKW IV and the Sherman M4, were been built with a short barreled 75mm for anti Infantry work. Both were upgunned when the tanks were called upon to shoot up enemy tanks. (PzKW IVF2, for example. The Shermans upgraded to the long barreled 75 and 76mm guns, but did not change the model designation... sigh.)

We actually DO have both versions of the Sherman in WITP - and several other cases where different weapons of the same caliber appear. There are more than a few 120mm and 127 mm guns, all with different ranges, ceilings (if AA or DP - not all are), and weight of shell.

As for penetration, it is a bit technical, both in real life and in the game.
Penetration is, for practical purposes, 1.75 times caliber for any weapon with a sufficiently strong shell if the muzzel velocity is in the range of 2700 fps, but ONLY at point blank range. Just what point blank range is changes with the range of the weapon. WITP figures out the actual range of a shot - or simulates doing so - by die rolls. Only sometimes do you have the rated penitration ability - other times you are at too great a range - or the blow is glancing - so you get less than the nominal amount. And one factor is the range of the weapon - so the "same" penetration figure may be at a range of 1 in one case, or 10 in another. Which isn't exactly the same after all, is it? As data input people, we have to understand that the database wants the worst (or best) case - and give it that so the code can work with the data it needs. But it is wrong to put in a value much greater - or much less - than the real value. And - I note - proof testing is remarkably consistent about this subject: it does not matter if you talk about a .30 caliber rifle bullet or a 18 inch shell - it does not matter if the test is done in Germany, Japan, the US or the UK. Ballistics is a science after all.

[mlees]

As for penetration, it is a bit technical, both in real life and in the game.
Penetration is, for practical purposes, 1.75 times caliber for any weapon with a sufficiently strong shell if the muzzel velocity is in the range of 2700 fps, but ONLY at point blank range. Just what point blank range is changes with the range of the weapon. WITP figures out the actual range of a shot - or simulates doing so - by die rolls. Only sometimes do you have the rated penitration ability - other times you are at too great a range - or the blow is glancing - so you get less than the nominal amount. And one factor is the range of the weapon - so the "same" penetration figure may be at a range of 1 in one case, or 10 in another. Which isn't exactly the same after all, is it? As data input people, we have to understand that the database wants the worst (or best) case - and give it that so the code can work with the data it needs. But it is wrong to put in a value much greater - or much less - than the real value. And - I note - proof testing is remarkably consistent about this subject: it does not matter if you talk about a .30 caliber rifle bullet or a 18 inch shell - it does not matter if the test is done in Germany, Japan, the US or the UK. Ballistics is a science after all.

Ummm. I did not make myself clear. (I tend to distract myself in casual spoken conversations as well. Very amusing for my cooworkers, frustrating for me.) Allow me to rephrase.

Muzzle velocity is a function of shell weight, propellant charge, and barrel condition (which includes length of barrel.)

So, the same calibre 75mm shell, propelled out the short barreled gun (I believe that the 75mm used a combined shot/propellant cartridge, so that means the same propellant charge is used), is going to have a lower muzzle velocity, than compared to one fired from the longer barreled gun variant. (If all other things, like barrel wear, are equal.)

That is because the longer barrel allows more of the propellant to burn (and provide thrust) before the shell has exited the bore.

Penetrating power is not based on merely the calibre of shell alone.

Now, with that said, I ask, can you set the penetration power of the longer barreled guns a notch higher than the shorter variants in the device database? If so, then I am worrying over nothing...

I remember reading my books on Dreadnought gunnery developement. They had to develope breech loaders to a "safe to use" level before they could introduce long barreled guns to the fleet. (The muzzle loaders had to retract, back far enough aboard ship for the loaders to be able to stuff a new propellant charge and shell down the muzzle. Too long of a barrel, and these guys are working outside the protection of armor.)

At the same time, they needed to work on gunpowders with a reliable burn rate property.(A quality control issue here, in modern terms.)

Once they fingered out the breech loader problems, they found that longer barrels gives longer range and higher hitting power. Finding that correct charge to length ratio came next.

The British HMS Dreadnought came with 12"/45's. The St. Vincent class had 12"/50's. The performance difference: The 12"/50, which used the same weight shell and propellant charge, gained 160ft/sec muzzle velocity, which translated into an extra 1/2 inch (12mm) of penetration at 3000 yards. Accuracy was worse due to "muzzle wobble". Apparently, the barrels were so long that, when fired, they "whipped"!

This prompted an eventual upsizing to the 13.5" weapon for their capital ships, with a gain of 10,000 foot-tons of energy with less muzzle velocity.

I find the evolution of the Battleship fascinating. A micrcosm of the Industrial Revolution.

[el cid again]

So, the same calibre 75mm shell, propelled out the short barreled gun (I believe that the 75mm used a combined shot/propellant cartridge, so that means the same propellant charge is used), is going to have a lower muzzle velocity, than compared to one fired from the longer barreled gun variant. (If all other things, like barrel wear, are equal.)

This is correct. Many 3 inch guns used fixed ammunition. Change in range was a function of elevation, not changing the number of bags of propellant, as in a heavy gun. In theory, a gun is a "single cylinder engine" and the longer the tube, the longer the "stroke" - the working time of the gas pressure - so the higher the velocity you get.

I am a techie guy - so I used qualfied language. Note I gave a value for mv. IF you greatly change mv, you will impact the penetration. Even so, for our purposes there is a remarkable similarity between guns: from .30 cal rifles to the biggest naval guns, a true gun almost always has a mv on the order of 2700 fps. The more you diviate from that norm, the fewer guns will be in your list. The highest production ammunition in history had a velocity of 4200 fps - and that is using a .22 sabot in a .30 caliber small arm. The fastest production ammunition in history not using a sabot had a velocity of 3600 fps - and that IS a .22! Both these limits date from a generation after WWII. Heavy guns of the sane type (we will ignore some exotic systems not really used by the armies and navies in PTO) rarely exceed 3000 fps by much - nor fal far below 2600 fps - with 2600 to 2800 being normal and covering a remarkable majority of weapons of all calibers. That consistency permits generation of a rule of thumb which works very well for simulation purposes. At 2700 fps penetration is 1.75 times caliber. Nice. I did some spot checking of datum points (where available) and found measured values dead on perfect, 1 mm different, etc. Not bad.

[el cid again]

Penetrating power is not based on merely the calibre of shell alone.

Nor did - or do - I say otherwise. I said that there were special cases: howitzers are given a lower value for example. Mortars and short guns a lower value still. Because - as you say - shorter bbl = lower mv resulting in less penetration.

[Mike Scholl]

ORIGINAL: mlees
So, the same calibre 75mm shell, propelled out the short barreled gun (I believe that the 75mm used a combined shot/propellant cartridge, so that means the same propellant charge is used), is going to have a lower muzzle velocity, than compared to one fired from the longer barreled gun variant. (If all other things, like barrel wear, are equal.)

Your thinking is basically accurate, but you need to remember that the size of the propellant charge is determined by the barrel length as well. There is little use in providing more propellant than can burn in the length of time the shell takes to travel up the bore. All that would provide is extra muzzle blast and recoil. Guns with longer barrels generally have larger propellant charges. Interestingly, higher muzzle velocity works against HE rounds, which provide better performance and fragmentation at lower velocities.

[mlees]

This is correct. Many 3 inch guns used fixed ammunition. Change in
<Snippity Snip> Not bad.

Nor did - or do - I say otherwise. I said that there were special cases: howitzers are given a lower value for example. Mortars and short guns a lower value still. Because - as you say - shorter bbl = lower mv resulting in less penetration.

OK. Looks like we are actually in agreement here...

I read:

I used 1.75 times caliber for high velocity guns penetration value at point blank range - which turns out to either be what WITP used or the measured data is very close.

To mean: "All same size rounds have the same penetration". But now I see you realise they dont.