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75 mm Vickers HV


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Daigensui #1 Posted Feb 08 2013 - 10:55

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Short and simple: Anyone know the muzzle velocity of the AP shells for the 75 mm Vickers HV? According to this site:

The M61 weighed 6.77 kg and was fired at 808 m/s from the Vickers HV for a muzzle energy of 2,200 kJ, compared with 620 m/s from the US tank guns (1,300 kJ). As a result, penetration went up from about 60mm to an estimated 87mm - not a huge amount more than the 6 pdr 7 cwt, but with a vastly more effective HE shell.



So, was the muzzle velocity only 808 m/s?

Daigensui #2 Posted Feb 11 2013 - 21:57

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Nothing?

laddpadd #3 Posted Feb 11 2013 - 22:35

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What, r u speaking in english? muzzle velocity?

Okinoshima #4 Posted Feb 11 2013 - 22:42

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View Postladdpadd, on Feb 11 2013 - 22:35, said:

What, r u speaking in english? muzzle velocity?

If only down voting was still around! :facepalmic:

Slakrrrrrr #5 Posted Feb 12 2013 - 00:59

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View PostOkinoshima, on Feb 11 2013 - 22:42, said:

If only down voting was still around! :facepalmic:
up voting still is!

Richardsen #6 Posted Feb 12 2013 - 03:54

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View PostKankou, on Feb 08 2013 - 10:55, said:

Short and simple: Anyone know the muzzle velocity of the AP shells for the 75 mm Vickers HV? According to this site:

The M61 weighed 6.77 kg and was fired at 808 m/s from the Vickers HV for a muzzle energy of 2,200 kJ, compared with 620 m/s from the US tank guns (1,300 kJ). As a result, penetration went up from about 60mm to an estimated 87mm - not a huge amount more than the 6 pdr 7 cwt, but with a vastly more effective HE shell.



So, was the muzzle velocity only 808 m/s?

I only found this. They state the same figure as you do. And 87 mm @ 30º/1000 m is a very good figure for a 75 mm gun; if we compare it with the KwK 40 (a very good and sound 75 mm tank gun) we can see that it is slightly superior, both in terms of penetration and muzzle velocity. However, I don´t know the differences in projectile weight and propellant charge, as perhaps the brits were using a bigger charge in order to obtain this performance.

Edited by Richardsen, Feb 12 2013 - 04:00.


Zergling #7 Posted Feb 12 2013 - 04:37

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Ooooh, nice job finding information on this gun; I hadn't seen a peep about it other than references to failed installations in the Cromwell and Churchill tanks.

87mm penetration is clearly too low for a 100 meter/0 degree from vertical criteria though, so that must be for angled penetration and/or longer range.


Here's De Marre results for this gun:

Using 76mm M1A1 firing M62 APCBC (7.00 kg) at 792 m/s velocity for 131mm penetration as reference = 133mm
Using 57mm 6 Pounder Mk V firing Mk.1T AP (2.86 kg) at 892 m/s velocity for 110mm penetration as reference = 132mm
Using 76mm 17 Pounder firing Mk.8T APCBC (7.71 kg) at 884 m/s velocity for 171mm penetration as reference = 139mm

Overall a bit lower than the 145mm penetration ingame, but compared to the later-war 17 Pounder shells, not significantly so.

The 145mm penetration for this gun is reasonably accurate, probably within 10% of what this gun could achieve IRL.



76mm M1A1:
Shell Weight = 7.00 kg (M62 APCBC)
Muzzle Velocity = 792 m/s
Kinetic Energy = 2133 kj
KE Density = 47.01 kj / cm^2

75mm Vickers HV:
Shell Weight = 6.77 kg
Muzzle Velocity = 808 m/s
Kinetic Energy = 2210 kj
KE Density = 50.02 kj / cm^2

Hmm... this gun wasn't actually that much better than the 76mm M1A1 in terms of kinetic energy performance; I guess the increased penetration is mostly from increased shell quality.

Chopa #8 Posted Feb 12 2013 - 04:41

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http://208.84.116.22...showtopic=35631

"The original 75mm HV used the cartridge case of the 3 inch 20 cwt AA gun (developed in WW1, still in British service in WW2), necked down from 76.2mm to 75mm. The cartridge was intended to use US 75mm tank gun projectiles: the M61 APCBC (14.92 lbs) and the M48 HE (14.6 lbs) as used with a smaller cartridge case in the M2 and M3 tank guns (M3 and M4 tanks) and the M4 and M5 aircraft guns (B-25G/H). Muzzle velocity with the M61 was calculated to be 2,650 fps in a new gun (2,600 fps assumed in comparisons) compared with 2,030 fps in the M3 tank gun, but it was felt that the M48 shell wouldn't be able to tolerate such a high chamber pressure so it was downloaded to 1,500 fps (35,840 psi rather than 49,280 psi for the APCBC).
Estimated armour penetration figures for the 75mm HV firing an M61 projectile were prepared. These showed a figure of 87mm at 1000 yards/30 degrees compared with c.60mm for the M3 tank gun. The performance of the 75mm HV was therefore calculated to be about the same as the US 76mm tank gun, although the 75mm M48 HE shell was much more effective than the 76mm's M42.

The only difference between the 75mm HV and the production 77mm was the fractional difference in calibre: the 77mm cartridge case was therefore exactly the same as that for the 3 inch 20 cwt, although the projectiles were different and it was loaded to a much higher performance. The 77mm's APCBC projectile from the 17 pdr (which did actually weigh 17 lb) delivered far better penetration than the 75mm HV: 108 mm at 1000 yards/30 degrees. With APDS, penetration increased to 165mm. Conversely, the 77mm's HE shell (15.4 lb) was no better than the 76mm's (in both cases, they suffered from the thicker shell walls needed to resist the high pressures). Later HE shells for the 17 pdr/77mm were much more effective as they were loaded to a lower velocity and pressure, allowing thinner walled shells to be used."

   By the same Tony Williams who wrote the site you quote. So it looks like even the guy who is actively researching this topic is getting conflicting data.
   Having written a few corporate proposals for British Industry, I am only too aware that there are "Lies, Damned Lies, and Statistics". Data is trimmed to support the proposal being made. Any Vickers data will support their argument....If any exists.
   Fire 100 rounds from the same production batch downrange and you will get 100 different holes, and 100 different penetration figures, depending on such vagaries as wind, atmospheric pressure, yaw at point of impact, armour angle and quality of metalurgy, charge age, condition, and production variances..... And the gunners' inside leg measurement.
   There is no exact number, just a range as Tony Williams seems to be concluding. At the end of the day WG will use whatever values they please for "Gameplay Reasons" anyway, so I wouldn't get your thong in a wad over it.

   Regards  Chopa

Zergling #9 Posted Feb 12 2013 - 04:59

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So... the 87mm penetration is for 30 degrees from vertical, 1000 yards range.

Converting that down...

To 0 degrees from vertical = 106-111mm (depending on which slope modifiers are used)
To 100 meters range = 128-134mm

128-134mm is almost exactly what the De Marre equation predicted using the 76mm M1A1 and 6 Pounder guns as reference.

Given the shell quality was probably lower than the later 17 Pounder Mk.8T APCBC, I think it is probable the Vickers HV's 145mm penetration is too high in game; it should probably be reduced to around 130-135mm.

Ogopogo #10 Posted Feb 12 2013 - 05:17

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View PostZergling, on Feb 12 2013 - 04:59, said:

So... the 87mm penetration is for 30 degrees from vertical, 1000 yards range.

Converting that down...

To 0 degrees from vertical = 106-111mm (depending on which slope modifiers are used)
To 100 meters range = 128-134mm

128-134mm is almost exactly what the De Marre equation predicted using the 76mm M1A1 and 6 Pounder guns as reference.

Given the shell quality was probably lower than the later 17 Pounder Mk.8T APCBC, I think it is probable the Vickers HV's 145mm penetration is too high in game; it should probably be reduced to around 130-135mm.

Well, in real life, slope does tend to have more of an effect. For instance the 20 pounder APDS when fired 500m at vertical armor can penetrate 300mm. When sloped 30 degrees at the same distance, it is only 240mm. When sloped at 60 degrees, the shell can only penetrate 80mm of armour.
http://www.wwiivehic...tion-tables.asp

Zergling #11 Posted Feb 12 2013 - 05:39

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View PostOgopogo, on Feb 12 2013 - 05:17, said:

Well, in real life, slope does tend to have more of an effect. For instance the 20 pounder APDS when fired 500m at vertical armor can penetrate 300mm. When sloped 30 degrees at the same distance, it is only 240mm. When sloped at 60 degrees, the shell can only penetrate 80mm of armour.
http://www.wwiivehic...tion-tables.asp

Slope effects were largely a function of Armor Thickness/Shell Diameter ratio though. Small, thin, APDS penetrators have some pretty big slope effect modifiers as a result.
That said, the slope modifier for the 30 degree slope in your above example is only 1.25, which is actually fairly small for APDS.

The 60 degree modifier is 3.75, which is rather high; tungsten APDS tends to have unusual slope effects like that.


I converted the 30 degree slope effect for the 75mm Vickers HV using calculations from WW II BALLISTICS: Armor and Gunnery, by L. Bird and R. Livingston.
For a 75mm projectile against 87mm thick armor, the slope effects for APCBC shell type produced a 1.279 modifier. For an uncapped AP shell type a 1.220 modifier.

For USA and UK produced APCBC shells I often use both with a 'min-max' result like above, because I find the APCBC shell modifiers are sometimes a bit too high for USA/UK APCBC shells; they seem most accurate for German APCBC.
In this case, the APCBC slope modifier agrees most with the De Marre extrapolated results, although the difference between the APCBC and AP slope modifiers is small enough to not be significant anyway.

Daigensui #12 Posted Feb 12 2013 - 07:24

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View PostChopa, on Feb 12 2013 - 04:41, said:

   There is no exact number, just a range as Tony Williams seems to be concluding. At the end of the day WG will use whatever values they please for "Gameplay Reasons" anyway, so I wouldn't get your thong in a wad over it.

I needed the info for something I was working on with Zergling. Thanks for the help.




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