Is that a gun in your pocket?

[Stokesy44]

Hi Guys

Being relatively new to armour, can someone tell me the physics behind what determines whether a gun is high velocity or not? I have a good (fair)smattering of tank knowledge and know the Panther had a gun roughly the same calibre as the Sherman - but why was the Panther's gun a high velocity shooter and the Sherman's not?

I know all about Fireflys and the Easy 8 with its 76mm gun etc etc. What I'm interested in is the science. Why was the 76mm so much better a weapon than the Sherman's original 75mm?

I'm feeling a bit Homer Simpson, something must have fallen out of my brain earlier today so I've got some room for a bit of new knowledge.

[HamilkarBarkas]

The gun of the Panther tank was probably the most powerful 75mm gun ever made. It was in certain ranges more powerful than the Tiger´s 88mm. The reason behind this is the barrel lenght and the amount of propellant. A long barrel provides a higher end velocity for the shell, because the projectile has more time and distance to accelerate with the explosion of the propellant behind the shell. its like the lenght of a catapult arm. with a spoon you can not outrange a shovel catapult. i think this is an appropriate comparison.

[SMAddict66]

I concur, length of barrel combined with amount of explosive force behind it gives a greater velocity at the muzzle.

So size of the nail combined with size of hammer ...

[MarkVerploeg]

The big differnce between the Sherman's 75 and 76 mm guns was found in both the lenght of the barrel (76mm had a longer barrel) and the round itself
The 76mm shell has a much bigger casing wich means more explosive power to fire it
Another aspect it the weight of the projectile
A heavier round doesn't loose that much speed (arty rounds are heavy but most can fly over 20km or more)
Anti tank and tank guns have that aswell
High explosive rounds don't require a long barrel as they don't need the speed a AT round needs to penetrate armor
They just don't penetrate but explode on inpact

A funny thing about the Sherman guns is that the USMC had the chance to upgrade from the 75 to the 76 wich was the Army's prefered gun
The 75 HE shell was actually better then the 76 mm version and as the Marines fired much more HE shells for things like bunkers and buildings they actually kept all the 75mm guns and declined on using the 76mm gun wich was better for using AT rounds
Japanese tanks where lightly armored and the 75mm AT round was more then enough to destroy them

But in general you can see if it is a high velocity gun by looking at the barrel
Longer barrels are most likely for high velocity guns
Some of the better known guns in this class can be found on the Panther ,King Tiger and Firefly with the English 17pdr wich was a very good gun and one of the few guns to form a thread for Tiger 1 tanks

[Stokesy44]

Brilliant. Thanks Guys. Much appreciated.

[digger303]

Another fact is with the longer gun and heavy projectiles a slower burning powder is used so that the whole length of the gun is used to increase velocity.
I'm sure the engineers can explain that better. There was a rail-gun that had propellant charges positioned along the whole length of the barrel to gain more range. As the projectile passed a charge it would ignite to give it more boost and so on. In theory a range of 120km was possible, but they only managed 60km.

[ForbesHutton]

You're probably thinking of the Super-Gun "Project Babylon" designed by the Canadian Gerald Turnbull. Built in Iraq for Saddam, the claim was it was to launch satellites, but it would have also been able to shell Israel. Turnbull was assassinated and Israel is wildly assumed to be behind it.

https://en.wikipedia.org/wiki/Project_Babylon

Back to ballistics:
You can put as much powder as you want behind a shell, IF the chamber is strong enough to contain and direct the explosion. Even with a strong chamber, the more sudden the acceleration of the projectile, the more damage (wear) will be inflicted on the rifling at the throat (the chamber end) of the barrel. Once you have too much wear at the throat, too much of the gas will move around the projectile and once it's in front of the projectile it will both slow the projectile and also unbalance it as it leaves the barrel, affecting accuracy. Very high velocity projectiles will wear the rifling along the length of the barrel and at some point will no longer spin the projectile, resulting in a complete lose of accuracy, this is known as a "shot out" barrel.

So while you could have a very short barrel firing very high velocity rounds, with a strong enough breach, the gun itself would be a engineering problem as it would be badly unbalanced from front to rear, and in the case of a tank, the breach would take up too much of the turret.

The normal solution is to move to a longer barrel, with a slower burning (exploding) powder. This slows the acceleration down but still gives the same muzzle velocity while lengthening the life of the barrel.

If we use the .22 rimfire round as an example, the same .22 rounds can be fired from both a handgun or rifle, but it will have twice the muzzle velocity in the rifles.

The weight of the projectile also affects velocity. Bullets are weighed in grains (64.79891 milligrams) and if we take the 9mm Parabellum round (also known as the 9mm Luger) the lightest bullet weights 115 grains and will reach 1200 feet per second from a 4.5" barrel. A 147 grain 9mm bullet fired from the same barrel will reach 950 feet per second (this is a sub-sonic speed, useful for suppressed (silenced) guns as the supersonic "crack" of the rounds exceeding the speed of sound is far louder than the sound level of the gun actually firing, so a supersonic bullet fired from a suppressed gun is self defeating.). The weight of the projectile can be varied, depending on requirement by making it longer or shorter (you can't vary the width and stay in the same caliber). More scientific stuff, since the overall length of the cartridge (the bullet and shell/casing combined) has a fixed maximum, or it would be too long to fit in the chamber, the extra length of your projectile (for the extra weight) has to be contained inside the shell/casing. If the projectile ends up seated to far back in the casing, 1) the amount of space for the powder is reduced, and 2) won't leave enough room for a fast burning powder to properly expand as a gas, blown apart the shell/casing and the breach if the breach isn't strong enough to contain the energy.

There's tons to know about ballistics, and I know a tiny fraction of it, but there are books galore on how to load small arms ammunition and the ballistics of bigger guns. I know enough to satisfy my own curiosity and keep myself safe with firearms, but if you want you can have a whole other hobby (or even career) with the study of ballistics.

....won't even start with penetration...

[MarkVerploeg]

There was a long range arty gun like that in WWI
They commonly called it the Paris gun with a range of about 70km
It was a German gun wich was basicly made by welding 3 barrels to eachother and use a lot of propellant
It was one of the larger guns ever made (lenght wise)

[Stokesy44]

Fascinating. So the amount of propellant is governed by the strength of the breach (and there's only so much you can do before size is an issue). A longer barrel allows the explosive force behind the projectile to build up for longer creating an increased velocity when the projectile leaves the barrel.

Have to admit, one of my thoughts was why not just put more powder behind shell - what do I know eh?

There was a rail-gun that had propellant charges positioned along the whole length of the barrel to gain more range. As the projectile passed a charge it would ignite to give it more boost and so on. In theory a range of 120km was possible, but they only managed 60km.

The Germans were building such a weapon in the Pas de Calais but the Allies over ran it before it could be finished - thankfully.

Next up is find out why sabot ammunition is deadlier than normal AP shells. I'll do my own research as there's only so many times you can go to the shop before they start charging you

[digger303]

There was a long range arty gun like that in WWI
They commonly called it the Paris gun with a range of about 70km
It was a German gun wich was basicly made by welding 3 barrels to eachother and use a lot of propellant
It was one of the larger guns ever made (lenght wise)

It was called the Hochdruckpumpe or high pressure pump or V3. It saw service in the Ardennes from Dec 30 1944.
Usually positioned on the side of a hill in order to get enough elevation. The gun was a smooth bore and 123 metres long FIRING A 90kg shell from a 16cm barrel

Ps there is a huge advantage in using propellants of different burn rates otherwise all we would need is one type for all uses rifles , pistols to naval guns.

[MarkVerploeg]

There was a long range arty gun like that in WWI
They commonly called it the Paris gun with a range of about 70km
It was a German gun wich was basicly made by welding 3 barrels to eachother and use a lot of propellant
It was one of the larger guns ever made (lenght wise)

It was called the Hochdruckpumpe or high pressure pump or V3. It saw service in the Ardennes from Dec 30 1944.
Usually positioned on the side of a hill in order to get enough elevation. The gun was a smooth bore and 123 metres long FIRING A 90kg shell from a 16cm barrel

Ps there is a huge advantage in using propellants of different burn rates otherwise all we would need is one type for all uses rifles , pistols to naval guns.

I didn't mean the V3
In WWI the German had this gun
It was stationned near the Belgium border and hit Paris multiple times

It consists of 3 barrels that where welded together and had a support construction to keep it straight as the weight was making it bend
This gun had a range of about 70 km but apperantly some rounds went a bit further if they didn't had a head wind to slow them down

[digger303]

wow looks very jerry rigged....sorry for the pun...but does look a bit rickety.
I realise you were talking about ww1, but I hadn't seen this pic so glad I have now. I was lazy and put all my info into the one post sorry for the mix up.

[MarkVerploeg]

wow looks very jerry rigged....sorry for the pun...but does look a bit rickety.
I realise you were talking about ww1, but I hadn't seen this pic so glad I have now. I was lazy and put all my info into the one post sorry for the mix up.

No problem mate
We can't know everything and a picture can help to clarify things (worked this time)
It doesn't look very sturdy but it actually was pretty succecfull
The rigging was only there to keep the barrel from bending

[digger303]

wonder how vicious the recoil was

[MarkVerploeg]

I don't know
It is a railgun so it probably wasn't that much as the entire car would slide back a bit and the gun would not hit thr ground
It was a 16 or 21 cm gun so it sure would have some recoil
But if you look at the large naval guns like on the USS New Jersey then you can see that the recoil for such a gun isn't as big as you would think

[wookiee76]

Discarding sabot ammunition is deadlier because it is a small diameter dart type of affair made out of a super heavy alloy, usually tungsten i believe which due to kinetics/physics etc means it is able to punch through much thicker armour due to having similar mass and a smaller profile, they tend not to have explosive components though, relying more on the sheer damage caused by a few kilos of tungsten ricocheting around inside the tank, if they do have an explosive charge I'm lead to believe it is at the rear of the round and explodes inside the target.

[digger303]

I don't know
It is a railgun so it probably wasn't that much as the entire car would slide back a bit and the gun would not hit thr ground
It was a 16 or 21 cm gun so it sure would have some recoil
But if you look at the large naval guns like on the USS New Jersey then you can see that the recoil for such a gun isn't as big as you would think

I have seen a full broadside from the Missouri ( not sure of the spelling) and the whole ship almost disappears in smoke and flame and the whole ship rolls a lot and thats a lot of tonnage to move.

They must have the railcar chocked so it stays in place. No health and safety then...not a earmuff to be found.

[MarkVerploeg]

I don't know
It is a railgun so it probably wasn't that much as the entire car would slide back a bit and the gun would not hit thr ground
It was a 16 or 21 cm gun so it sure would have some recoil
But if you look at the large naval guns like on the USS New Jersey then you can see that the recoil for such a gun isn't as big as you would think

I have seen a full broadside from the Missouri ( not sure of the spelling) and the whole ship almost disappears in smoke and flame and the whole ship rolls a lot and thats a lot of tonnage to move.

They must have the railcar chocked so it stays in place. No health and safety then...not a earmuff to be found.

I'm not sure what they did in WWI but in WWII it was pretty common to have a small locomotive attached to the gun wagon to keep it place and to push it back
Except on a turntable ad that would be a bit too big
It will depend on the angle of the gun aswell

[Stokesy44]

Discarding sabot ammunition is deadlier because it is a small diameter dart type of affair made out of a super heavy alloy, usually tungsten i believe which due to kinetics/physics etc means it is able to punch through much thicker armour due to having similar mass and a smaller profile, they tend not to have explosive components though, relying more on the sheer damage caused by a few kilos of tungsten ricocheting around inside the tank, if they do have an explosive charge I'm lead to believe it is at the rear of the round and explodes inside the target.

How the APDS came about..... (I've been studying!)

The concept came about because of the search for better AP penetration against AFVs. What was needed was a higher impact (terminal velocity) round or a round with a larger mass. It was soon realised that bigger shells were not the answer because no existing weapons could fire them and the new guns required would have been too heavy to fit into existing AFVs or too cumbersome to be used as anti-tank guns. Greater velocity applied to existing steel AP rounds didn't work either because the shell shattered on impact at velocities over 850 m/s.

The answer was tungsten carbide. It was twice as dense as steel so the designers reasoned it didn't need to be as big as a standard AP round. A slender dart of the new material, when fitted inside a new full size lightweight sleeve worked with existing guns. The projectile and sleeve was only half the weigh of a similar calibre AP round so the explosive gases behind the round in the barrel accelerated it at a much faster rate causing a much higher muzzle velocity to be achieved.

The initial version was called the APCR or Armour Piercing Composite Rigid. The problem was the sleeve didn't detach on leaving the barrel and it made the projectile slow down through the air due its poor density to size ratio. The British solved the problem with the APDS, the Armour Piercing Discarding Sabot. The sleeve came away from the core on leaving the barrel so the projectile's density to size ratio was massively increased leading to a correspondingly higher terminal velocity - well in advance of those achieved with the APCR and all standard AP rounds at the time.

Next up I aim to explore that other great unknown in the universe - WOMEN

[MarkVerploeg]

So i guess this is good bye then
No man ever explored that subject and came back with his sanity intact

[Stokesy44]

So i guess this is good bye then
No man ever explored that subject and came back with his sanity intact

Wibble