Armor Penetration - 20mm vs. .50 cal.

[delcyros]

2.) What about specialised tank hunters?
Lets take a Hs-129B1 for example. It figures 2 MG 17 (which we can neglect here) and two 20 mm MG151 (firing 117 gr. AP rounds). Early Hs-129B replaced them by the 15 mm variant of the same gun (firing 72 gr. AP-rounds or 52 gr. APR-rounds). The Hs-129B1/R2 variant figured a high velocity 30 mm MK 101 as belly centerline gun (firing 330 gr. AP-rounds).

Lets compare it with an early T-34 tank. This tank features well placed inclined armor plates on the front (40mm@60), sides (40 mm @ 40 degrees), and rear (40mm at 42 degrees). It´s roof is protected by 20 mm material.
The quality of soviet armor is variying heavily. Thinner plates, such as used in the T-34 are of middle to high hardness but comparably brittle (down to 14% elongation).

The inclined armor plates are a disadvantage for the T-34 against air attacks. They REDUCE the impact obliquity if the plane dives to almost zero. The Hs-129B is aclumsy and slower plane, but capable for short timed dives up to 40 degrees. If the Hs-129 dives to the 62 dregrees inclined front plate of a T-34 at 40 degrees, the impact obliquity is close to 20 degrees only. Can a 20 mm MG 151/20 round penetrate the T-34 front? No. It wouldn´t be in the 151/20´s possible striking velocities. Can the MG 151/20 penetrate the rear plates? No. It would require 2.720 ft./s. striking velocity to do so at best possible impact angles (0 degrees obliquity is barely possible at 40 degrees dive). The armour is vulnarable at 12 m distance as long as the plane keeps 420 Km/h airtspeed! No chance to recover from the dive. Suicide only. Can the MK 101 30 mm penetrate the T-34´s front armor under these circumstances?
Surely. I even grant them a considerable wide window for penetration. Considering 15 degrees difference in impact obliquity (either longtudinally or vertically) the 30 mm AP round would only need 644 m/s. striking velocity for full penetration, reduced to 635 m/s. at best possible impact angle. The initial velocity of a MK 101 is 920 m/s+100 m/s for the planes velocity (thanks MAGISTER!). According to the ballistic estimations of the shell, there is full penetration indicated at any range closer than around 480 m distance (according to Lunatics calculation of the somehow inferior MK 103)! The roof and sides are vulnarable, too. At closer distance (~330m and closer), the front is vulnarable as well. I would even go so far and postulate that the MG 151/15mm AP round has a reasonable chance to pierce the T-34´s rear at very close (772 m/s. needed striking velocity: ~160 m distance), the same gun with tungsten tipped APR ammo will have a reasonable chance to penetrate at close range as well (up to 220 m for the front, 290 m for the rear). It is somehow questionable if a dive recovery is possible at these distances. It cannot be excluded.
I conclude that the 30 mm MK 101 (and the MK103 as well) is able to defeat the armour of early T-34 at most plates and for a wide window of impact angles. Neither the MG151/20 nor the LMG´s present any harm for this main battle tank. The MG 151/15 has at least a chance to do so for very close (AP-rounds) or close (APR-rounds) distances.

 

[schwarzpanzer]

Hi delcyros,

Lets compare it with an early T-34 tank. This tank features well placed inclined armor plates on the front (40mm@60)

45mm @ 60 degrees IIRC. Some had 60mm @ varying angles (60 degrees for non-applique).

Can the MG 151/20 penetrate the rear plates? No.

It could possibly go through the grills, or rip access hatches off etc. With a high RoF, this is likely.

Thinner plates, such as used in the T-34 are of middle to high hardness but comparably brittle

The spalling could cause a KO too.


I suppose gravity and the planes speed would help, but I doubt a MK108 HE round would hurt a T34?


I think the ShVaK is interesting as it was used on the T60 tank and planes and fired API.


The IL2's HEAT bombs seem a good idea?

 

[delcyros]

Yes, Schwarzpanzer.
45mm frontal, true. My mistake (I actually calculated with 45, kind of typing error). 20mm rounds may went through vents and openings as well, but I doubt that they can defeat the armourplate, even if we consider multiple hits. Damage may occur by non penetrating effects (spalling, "discs", mechaical malfunctions) but this is subject to accidents. Not wanting to deny them, though.
I cannot exclude (but I don´t believe) that a MK 108 AP-round will hurt a T-34, at least for it´s sides, roofs and rear plates under favourable impact obliquitys. If the APround has the same weight and muzzle velocity of the HE mine round it will penetrate at 691 m/s striking velocity. Thats a large "what if". Take a Me-262 with 900 Km/h speed at dive and the projectiles gains enough velocity at close range to defeat 45 mm of T-34 plates. The probable multiple hits makes penetration more plausible. 100 m distance or closer only. This seems to me quite too close for a 900 km/h diving Me for making dive recovery possible.

 

[Pinball Rick]

I am very interested in a picture inside the wing of an American WW2 Fighter 50 Cal Guns. I need to see how 3- 50 Cal guns hook up to the ammo boxes.( ie P-40?) I've seen pictures of the ammo access door and gun door, but not one actually looking in the door at the guns or the ammo. Where can I get these pictures?
Thanks
Pinball Rick

 

[drgondog]

1.) Hawker Typhoon Ib with four 20 mm Hispano Suiza MK II. The MK II has a slightly improved AP-capabilty thanks to a higher muzzle velocity. It fires a 130 gr. weight AP projectile with crh4 nose (ogaviel) at 880 m/sec. muzzle velocity. According to Lunatics database it´s striking velocitys in flight are as following:
0 m: 879 m/s; 100 m: 807 m/s.; 200 m: 738 m/s.; 300 m: 673 m/s.; 400m: 612 m/s. The initial penetration is up to 53 mm armor grade material at 0 degrees impact angle.
It´s target is the vaunted Tiger I tank (compare armor scheme of early models in clean configuration below). It´s armor is very ductile and comparably soft. 255-265 Brinell hardness with close to 21% elongation makes it one of the finest ww2 tank armors. The Tiger depends on verticle armor , this may be a disadvantage in close combat tank vs. tank, but as we will see, it makes it very problematic to attack from the air. The only theoretically penetratable armor area are the horizontal turret and hull roofs. Both have 28 mm (1.1") armor.
Since full 90 degrees dives are excluded for Typhoons and even 60 degrees doesn´t seem plausible to me (this is a fighter bomber, not a dive bomber) I expect an approach angle between 15 and 45 degrees from the vertical. This will imply an impact obliquity of between 45 and 75 degrees at perfect longitudinal direction. Let´s assume the pilot is a real scary one and will dive in for 45 degrees. He correctly aims for the tanks roof and opens fire at 600 m distance, leaving enough altitude (around 1000ft.) to recover from the dive. Are 20mm MKII able to hurt the Tiger?
Impossible. The aircraft round will have a striking velocity of 1.660 ft./sec. (+, since it will benefit from 45 degrees fall), but it would need 800 ft. /sec. more to penetrate 1.1" of Tiger-I armor. How close has the Typhoon to dive at the Tiger-I for succefull penetration of it´s guns at 45 degrees?
Can tell You. With 730 m/sec. minimum striking velocity the limit is reached at between 210 and 230 m distance. There would be only 300 ft. altitude left to recover from a 45 degrees five. This sounds like a dirty nap for me.

Nicely done, D

 

[Soren]

The HC rockets often carried by the Typhoon Tempests were however a serious threat to any German tank, as so thuroughly demonstrated in Normandy.

 

[Tony Williams]

The initial penetration is up to 53 mm armor grade material at 0 degrees impact angle.

That seems high to me. The best figures I've seen quoted for the Hispano AP (American) shot are 31-39mm at 300m and 0 degrees, depending on the ammo quality.

Anyway, the RAF seems to have made little use of AP ammo. Standard belt loading for the Hispano by 1944 was equal numbers of SAPI and HEI - and the SAPI couldn't get through much more than 20mm (it was about as good as the .50 API in penetration - but contained over ten times as much incendiary material).

 

[drgondog]

That seems high to me. The best figures I've seen quoted for the Hispano AP (American) shot are 31-39mm at 300m and 0 degrees, depending on the ammo quality.

Anyway, the RAF seems to have made little use of AP ammo. Standard belt loading for the Hispano by 1944 was equal numbers of SAPI and HEI - and the SAPI couldn't get through much more than 20mm (it was about as good as the .50 API in penetration - but contained over ten times as much incendiary material).

Tony - I just commented that it was nice analysis - The quote you attributed to me was I think, from Delcyros a little further up?

 

[HoHun]

Hi Tony,

>Anyway, the RAF seems to have made little use of AP ammo. Standard belt loading for the Hispano by 1944 was equal numbers of SAPI and HEI - and the SAPI couldn't get through much more than 20mm (it was about as good as the .50 API in penetration - but contained over ten times as much incendiary material).

Recently, the question was raised how much penetration the various Hispano II ammunition types would have against an armour plate struck at 20 degrees angle measured from the plane of the armour plate to the projectile - in other words, at a very shallow angle.

Do you perhaps have any figures that might answer the question? They would be much appreciated!

Regards,

Henning (HoHun)

 

[NeilStirling]

Interesting information here Hispano 20mm AP ammuntion - The Development, production and performance

A great deal of information!

Neil.

 

[Tony Williams]

Hi Henning,

I have the following from Peter Labbett's booklet on the British Hispano ammo:

AP Mk 1.z - never issued

AP Mk 2.z (first record, August 1942) - steel shot with bakelite ballistic cap, weight 140g. Intended to penetrate 36mm/200m, 28mm/400m, 22mm/600m, all figures striking at 0 degrees. On tests against German tanks in North Africa, it was found to be ineffective.

AP Mk 3.z - composite shot with tungsten core, weight 96.5g. Intended to penetrate 60mm of IT plate at 200m/20 degrees, but never adopted (inaccurate)

I have been unable to determine how much use the RAF made of AP shot, but not a lot I suspect. If the AP couldn't penetrate tanks, but the SAPI could deal with anything else, then it made sense to stick with the SAPI.

Official US Army data sheets for the 20mm M75 (165g at 777 m/s) credit it with 18mm/500 yards/20 degrees (homogenous plate) or 16.5mm (face-hardened).

Somewhere I have a range/penetration graph for the US M75 (I filed it safely away...) from which I got the figures of 31-39mm 300m/0 degrees I quoted earlier.

 

[Tony Williams]

Interesting information here Hispano 20mm AP ammuntion - The Development, production and performance

A great deal of information!

Neil.

Yes, that's very interesting. The "Littlejohn" AP was the Mk 3.z I mentioned. I don't think that it was ever accepted for service.

The MK 4.z reverted to a one-piece steel shot, c.140g.

There were also AP-T rounds (Mk 1.z and Mk 2.z) which were one-piece steel, basically like the AP with a tracer in the cavity.

It still isn't clear how much actual use was made of any of the AP rounds, though.

 

[HoHun]

Hi Neil,

>Interesting information here Hispano 20mm AP ammuntion - The Development, production and performance

Wow, thanks a lot for the link! I love the level of detail on that site

Regards,

Henning (HoHun)

 

[HoHun]

Hi Tony,

>AP Mk 3.z - composite shot with tungsten core, weight 96.5g. Intended to penetrate 60mm of IT plate at 200m/20 degrees, but never adopted (inaccurate)

Looking at the figures, it seems that this is 20 degree off the line that is perpendicular to the armour? Measured that way, I'd probably have to ask for figures for a 70 degree impact angle.

If no figures for such impact angles exist, do you think it would be possible to calculate them from the right-angle impact figures by applying a cosinus factor? (I fear it might not be accurate, depending on whether the projectile "digs in" on impact or glances off, but that's just a layman's opinion!)

Regards,

Henning (HoHun)

 

[Tony Williams]

You have to be careful in dealing with striking angles, because there are two conventions: the current NATO one describes the most favourable angle of attack (perpendicular to the surface) as 90 degrees, but it has in the past been common to describe that as 0 degrees. The only safe figure to use is 45 degrees

If you take the best angle as 0 degrees, then the typical attack angles normally measured are 20 or 30 degrees.

I don't think that you can work out a simple formula for penetration at different attack angles, because it depends on the design of the projectile: some are less affected by hitting at an angle than others.

 

[HoHun]

Hi Tony,

>You have to be careful in dealing with striking angles, because there are two conventions: the current NATO one describes the most favourable angle of attack (perpendicular to the surface) as 90 degrees, but it has in the past been common to describe that as 0 degrees.

Thanks for pointing that out - I was really thinking of 20 degrees in the NATO convention sense.

I'd say the figures on the site are probably "old-style" measurements (deviation from the line perpendicular to the armour plane)?

Hispano 20mm AP ammuntion - The Development, production and performance

>I don't think that you can work out a simple formula for penetration at different attack angles, because it depends on the design of the projectile: some are less affected by hitting at an angle than others.

Thanks, that's what I expected - reality can be complex at times

Regards,

Henning (HoHun)

 

[Elvis]

... sectional density helps as the energy is focused on a smaller area...

Sectional Density has nothing to do with "focusing energy".
It gives the armourer an idea of how well the projectile will hold together, based on the bullet's density.
The higher the sectional density, the "harder" (or maybe "tougher"?) the target can be before the projectile disintegrates.
Bullet shape does have an affect on sectional density, but the way its explained above is a bit confusing.
The old reloaders adage was that the higher the sectional density, the lower the ballistic coefficient, which was a reflection of how bullet shape affected both quotients.

...this coming from a guy who used to read reloading manuals as a kid, in his spare time.



Elvis

 

[Soren]

Generally the higher the SD the higher the BC as-well (This is leaving out the crucial form factor ofcourse).

As for focusing energy all that matters is energy divided by frontal area, the higher the energy pr. area the higher the stress put on the target is.

 

[billswagger]

I don't claim to be an expert on the topic, but if the .50 cal weren't efficient enough then why were most p-47s and p-51s armed with them.

The 20mm was more efficient at killing tanks. Although .50 cal could be very disruptive on the ground, it was not enough to get through heavier tank armor.
So the solution with .50 cal was to hit the fuel carts pulled by the tanks. This wouldn't destroy the tanks but would keep them from moving once they ran out of gas. Some pilots also discovered that tanks weren't armored underneath, so they aimed at the base of the tanks with the .50 cal bouncing the bullets into the undercarriage, doing significant damage.

As for air to air combat...there weren't many fighters that could withstand .50 cal., especially eight or six of them. 20mm/30mm were more useful at hitting bombers and armored ground targets, but its use in the dogfight arena was discouraged if you had another armament to use.


Bill

 

[Elvis]

I don't claim to be an expert on the topic, but if the .50 cal weren't efficient enough then why were most p-47s and p-51s armed with them.

The 20mm was more efficient at killing tanks. Although .50 cal could be very disruptive on the ground, it was not enough to get through heavier tank armor.
So the solution with .50 cal was to hit the fuel carts pulled by the tanks. This wouldn't destroy the tanks but would keep them from moving once they ran out of gas. Some pilots also discovered that tanks weren't armored underneath, so they aimed at the base of the tanks with the .50 cal bouncing the bullets into the undercarriage, doing significant damage.

As for air to air combat...there weren't many fighters that could withstand .50 cal., especially eight or six of them. 20mm/30mm were more useful at hitting bombers and armored ground targets, but its use in the dogfight arena was discouraged if you had another armament to use.


Bill

What you're seeing is the evolution of armour vs. firepower as it existed at that time.
Up until WWII got going, a lot of planes, both fighters and bombers, were stil using 30 cal. weapons, since it was deemed that was enough (worked during The Great War!).
But designs got "better" and it was soon found that a larger, more powerful round could bring the plane down quicker, with fewer rounds being used.
The .50 was actually designed as an anit-tank weapon, because armour was still that thin during that time (and I'm referring to the time that is the later part of, or just after the end of, WWI).
WWII ended up being both the "Golden Age" and the "Swan Song" for the .50, as an effective gun caliber for fighters and bombers.
Korea showed everyone that it had become a "20mm game".
I believe that, even today, you won't find a round on any aircraft that is smaller than 20mm.
Thus, it all boils down to the old game of, "well if you're getting a bigger weapon, I'm getting more armour...and an even bigger weapon! "
(Sort of a "The-Art-of-Keeping-up-with-The-Jones's-Warfare" kind of mentality).
The reason the larger caliber guns weren't used as often during WWII was that their rate of fire, and their performance, was relatively low in those days.
This meant it was harder to hit to the target (less of the "shotgun effect") and was less effective when it did (compared to what it probably should've been).
With the advent (or rather, return) of multi-barrelled, fast firing weapons, projectile size and performance grew very quickly.
Now the rate of fire could match, or even surpass, the smaller caliber guns that had been in use, while utilizing what had become, a more effective round.



Elvis