Overkill or Target Practice?

Looks almsot the same, minus the barrel on the original blown off, and some metal sticking out from the hatch in the colour.
Plus the Russian site statged it was a JS-2, I would belive the Russian.

 

I like the idea of "kill verification" that was mentioned, but since this came up, I keep thinking of that hulk being in the middle of a firefight, catching stray rounds and other misses.

Hey, it could happen!

 

That is a good hypothises.




The 1s in Turret are 45s and in Hull are 2 76 (althoe I spoted only 1) unless the part that has an amolst circler hole (above the tacks) is considered 1.
This also coincides to another topic where someone was saying something about the Panther being impervious to 75mm of sherman, cause Russian 45mm could penetrate Panther.(the 2 on the turret)

 

Though it is true that the Panther's side armour was not nearly as impressive as its frontal armour (a mere 45-50mm) and could indeed be penetrated by the early Sherman's 75mm gun, it must be said that calibre isn't everything. The Russian 45mm gun was a dedicated AT gun with a long barrel and specialized ammunition; the American 75mm M3 was meant for infantry support and as such it had a short barrel, reducing its effectiveness against armour.

 

most people assume that the bigger the diameter of the gun the better it is. So a 50mm is better than a 37 and a 77 is better than a 76 which is better than a 75.

Very few people, except those who have actually bothered to read books on the subject, know that penetration is generally provided by velocity and the type of round rather than it's width. Few people know what makes a round travel faster is the calliber and ammount of propelant, often not knowing what calliber actually is.

Also from the pictures Tony has has posted I am very surprised between the size of different rounds of the same diameter which would represent the amount of propellant used in their firing.

I assume the German 88 turned out to be such a good AT gun was the fact that as an original heavy AA gun it was designed to fire it's round very far into the sky at a speed to make aiming easier which requires a lot of propelent and a good calliber.

FNG

 

AA guns like 88's don't hit the Lancasters fliing at 4000m up. Sorry, but the idea is that you fire a large shell, filled with explosives, that will explode close enough to the aircraft, and thus damaging it (fragmentation).

Your idea of AT gun is not consistent with all AT guns. It was previously discussed that APCR rounds, even though small in caliber, had greater armour piercing abilities, but that degraded with range, as opposed yo APCBC rounds.

For WW2, that is correct. Sorry. But elementar phisics tell us that bigger projectiles can store more energy, and so in case of impact, they are more deadly. Still, speeed is a factor too. It would be interesting to find out a relation between speed and weight of projectiles... If you want, we can discuss why some tanks are today fitted with a SMG or a riffled gun. WW2, we talk about riffled guns. And APCR rounds were in a short supply, even if the demand was huge, and even in allied hands.

 

Yup, that's a JS allright. Sorry for beeing in doubt. As for the Panther, the hits didn't kill it. Besides, the 76mm rounds hit from behind and sideways, thus the side armour was not hit at the ideal angle. Maibe didn't went all the way inn.

For the JS, I don't really see burning marks on it. Those should appear darker, especially where paint was burned. And that one is totaly wrecked. Blown up from the insight... Maybe an AT rocket hit the upper deck behind the turret?

 

obviously you are never going to hit a lancaster! That would be plain stupid, but you need to be in the ball park! Hence a high velocity. You are also firing vertically which is also heavy on energy.

APCR and APCBC are specialist rounds. What I am talking about is 2 guns firing the same type of ammo, plain basic AT rounds. Obviously you can not compare 2 similar guns firing 2 differing types of ammo. It would be like saying which is better, bitter or lager.

As for the bigger the better, that is not strictly true as you have said, the type of round makes such a difference. Besides the energy you refer to is momentum which is actually Mass X Velocity. On that basis a big slow round will be no better as an AT round than a fast small one. So velocity is very important.

Finally velocity is produced from the calliber and charge. 2 differently desigend 75mm guns firing plain AT rounds can have massivly difference performance.

FNG

PS, SMG? SubMachineGun? why would a tank be fitted with an SMG rather than an MG?

 

I hope you're saying sorry here because you're apologizing for the incorrectness of your own statement.

I've previously listed a few guns that were more powerful than others yet smaller in calibre: the 75mm on the Panther vs the 76mm on the Sherman, the 88mm on the Tiger II vs the 128mm on the Jagdtiger, etc.

 

So the 76 mm Sherman is more powerful than the 75 mm gun of the Panther?

Yes or No?

 

hell no.

 

Most AT guns of WWII, including tank guns, killed with kinetic energy (KE), and KE is far more influenced by speed (velocity) than size (mass).
The equation is KE = [(mass (M) times the square of the muzzle velocity (V)) divided by two] or:
KE = 0.5xMxV*2.
So KE increased much faster with more velocity (squared) than more mass. And of course the KE drops off rapidly with distance as the shell slows due to friction with the air, larger shells actually generating more friction due to a greater cross sectional area.

Muzzle velocity is influenced by rate of burn (faster is better) and amount of propellant (more is good) and the length of the barrel (the longer the barrel, the longer the propellant gases have to act on the shell. Optimum length was around 70 calibers). Maximum for WWII was around 1,000 meters/second. Larger shells may have more propellant, but they also have to act on a greater cross section and mass.

Muzzle velocity of guns varied greatly, but wasn't dependant on shell size. The German 75 mm/24 caliber gun firing 6.8 kg APCBC shells generated a muzzle velocity of 385 m/s, penetrating about 40 mm of steel (at 30 deg to vertical) at 100 m. The Panther's 75L70 gun had a muzzle velocity of 935m/s, penetrating over 135mm (at 30 deg) of steel at 100m, about the same as the Tiger I 88L56 10.2 kg APCBC shell at 773 m/s.
The same 75mm shell could produce vastly different penetration values due to muzzle velocity resulting from a longer barrel.
The Tiger II 88L71 guns had a muzzle velocity of 1,000 m/s with 10.2 kg APCBC rounds, with penetration values over 200mm at 100m.

 

To add something to canambridges message:
1) Althought larger shells generate more friction than smaller ones because of their greater cross-section, they could also have better sectional density which helps to retain velocity.
Generally larger shells travel much further than smaller ones.

2) When comparing low MV guns and high MV guns of same diameter shells, we have to remember that high MV guns are much heavier, cost much more and worn out much faster. Also, due to high pressure, HE-shells have much thicker walls and therefore have less space for bursting charge.

 

You are forgetting that the muzzle velocity is different of the terminal velocity (when it makes impact). Therefore wouldnt the KE decrease over distance as the velocity of the projectile?

 

I was thinking smooth bore gun (SMG). Thanks for the lesson, canambridge and Notmi.

Do potential energy add to kinetic energy at the point of impact?

 

I assume you mean gravitational potential energy? Not much as AT-guns tend to be direct fire guns and their shells wont go much higher than line of sight. Therefore they wont get much potential energy.

 

If that is true then why do these guns have a specific point-blank range?

 

Now you lost me. Care to explain with larger letters? :lol:

 

do you mean minimum range?

FNG

 

KE does decrease with range as the projectile velocity drops, due to friction with the air. See Notmi's post for the pro's and con's of larger shells travelling further.
A very simple rule of thumb is about 2% reduction in penetration per 100m.