Russian 122mm

[Reozil]

hmm i think that this table could be more like it really was

The 122mm L/43 and L/46 with APBC had penetration abilities as such:

100m: 201mm

250m: 194mm

500m: 183mm

750m: 172mm

1000m: 162mm

1250m: 152mm

1500m: 144mm

2000m: 129mm

2500m: 118mm

3000m: 108mm

[MikeyD]

Cite your sources, man!

A good deal of penetration data (including original source material) is extrapolation based on a formula, and may or may not mirror real life. I believe both the German and Russian gun tables

often incorporate phrases like "...represents the chance of piercing a target of X thickness 60% of the time", which implies a lot of variation.

The latest issue of 'AFV News' out of Canada just had an authoritative (and rather opaque) article on Russian penetration table models. Your source and BFC's source may simply be using the same data to get different results.

[rune]

Russian Sources disagree with your numbers.

http://www.battlefield.ru/guns/defin_4.html

Look for the D-25T tank gun used on the IS-2.

Rune

[JasonC]

The curious part of the current CMBB numbers is how fast the rated penetration falls with range.

First Rune you should understand the CP figures at Russian Battlefield are for 80% chance of penetration, where most numbers are for 50 50 chance. The 50-50 figure can be 5-7% higher.

CMBB gives the 122 a 5% higher figure than the RB CP figure at 500m, for instance. That is just what you'd expect from CP vs. 50-50 measures.

But at 1000m, the CMBB figure is 4% lower than the RB CP figure. The drop from 500 to 1000m is 6.6% according to RB, but 14.6% according to CMBB. Then at 2000m, the CMBB figure is only .85 times the RB CP figure. RB has the penetration falling 14% from 1000 to 2000 meters. CMBB has it falling 25%.

Over the whole distance from 500m to 2000m, CMBB shows a 19% greater drop in penetration than RB does - 35% overall compared to 20%.

Now compare the range envelope factors of other guns in CMBB. Side, gun, muzzle velocity, then percentages of 1000 and 2000 flat figures compared to the 500 figure.

Ger 75L48 750m/s 89% 70%

Ger 75L70 925m/s 89% 70%

Ger 88L56 773m/s 91% 74%

Ger 88L70 1018m/s 91% 74%

Rus 76L42 680m/s 88% 60%

Rus 85L55 800m/s 90% 74%

Rus 122L48 790m/s 85% 65%

Rus 152L29 600m/s 89% 71%

The Russian 152 looks like the German 75s, which are much lighter shells but higher muzzle velocity. The Russian 76, low muzzle velocity and shell weight, loses far more than the others at 2000m. It may be overstated. Its 2000m number also looks low. The Russian 85 looks like the German 88s in loss of penetration ability with range.

But then the 122, with a heavier shell than the Russian 85 and essentially the same muzzle velocity, loses more penetration going from 500m to 1000m than even the Russian 76mm. It loses more penetration going from 1000 to 2000 than the German 75L48 does, with a much lighter shell and marginally lower muzzle velocity.

You'd expect the heavier shell to conserve more of its penetration power with range than the lighter ones. That is just what you see with all the German guns, and the Russian 85 compared to the Russian 76. But not, for some unfathomable reason, the Russian 122.

The Russian 122 has a slightly higher muzzle velocity than the German 88L56. It has a much heavier shell. You expect it to maintain its momentum better against air resistence than the 88L56 does. If it had even the same range reduction factors, it would have 7% higher penetration at 1000m and 13.5% higher penetration at 2000m. 10% higher, one would interpolate, at 1500m (132 vs. 120).

These are not figures that are tactically unimportant. The range and side angle at which Tiger Is and Panther turret fronts become vunerable to the Russian 122 depends on them.

The Russian Battlefield figures for the range reduction factors for the Russian 122 are -

93% 80%

One wonders if the loss of velocity with range figures used for the CMBB estimates of 1000m and 2000m performance for the Russian 76 and 122 are based on rounds without ballistic caps. Capped ammo should not lose penetration ability with range significantly faster than German rounds of equal or lower mass and comparable muzzle velocity.

[rune]

But it doesn't change that his figures are off. The D-25T gun was noted for its poor AP performance. See:

http://www.battlefield.ru/is2_1.html

The effect only got better when the Germans changed their armor. See the section where the 122mm shell is shown.

An example, using the 5% figure at 90 degrees, [which is 0 degrees] at 1000 meters, 142mm X5%=149mm, he shows 162mm.

As for the drop off in penetration, would the larger shell have MORE air resistence then a thinner, smaller shell? Rexford, where are ya?

Rune

[ April 24, 2003, 03:36 PM: Message edited by: rune ]

[rexford]

Russian 122mm AP is an uncapped projectile with very poor ballistic shape (it's kinda blunt), 75L48 APCBC has a special cap that acts as a windscreen and lowers air resistance (streamlined looking).

From 0m to 1000m 122mm loses 21% of 0m penetration, 75L48 APCBC also loses 21%.

75L48 APCBC has better aerodynamic shape, 122mm AP has higher mass/diameter ratio (this is velocity staying power, explains why baseball can be thrown further than a hollow whiffle ball of same size as baseball).

122mm AP is also fired at a higher velocity than 75L48 APCBC, 792 m/s against 750 m/s, which helps to retain velocity over range.

75L48 "mass/diameter squared" ratio is 0.001209

122mm "mass/diameter squared" ratio is 0.00168

ratio is kg/millimeters squared

Penetration figures for 122mm AP from Russian Battlefield site are against FACE-HARDENED ARMOR. This is what Miles Krogfus' recent article indicated. 122mm AP penetrates about 162mm CP at 0m, 80% of successes, against face-hardened armor.

For 50% success, 162mm x 1.06 = 172mm against face-hardened armor.

My latest figures for 122mm AP penetration against homogeneous armor are:

197mm at 0m

192mm at 100m

175mm at 500m

156mm at 1000m

139mm at 1500m

123mm at 2000m

110mm at 2500m

098mm at 3000m

[rexford]

There's something else about the Russian penetration stats for 122mm AP that should be understood.

The velocity estimates versus range are really not very good.

Working backwards from penetration data (CP) on Russian Battlefield site, the muzzle and 2000m velocities work out to 780 and 640 m/s (ARTKOM equation in Miles Krogfus article).

122mm AP was actually fired at 792 m/s, and 2000m velocity was about 560 m/s.

I have access to a trajectory computer program that estimates velocity versus range, and 122mm AP is not going 640 m/s at 2000m. Input to program was very good drawing of projectile shape.

[rune]

Thank you rexford...

The figures shown by rexford are still much lower then originally stated. I do not know where he got those figures, as they do not match anything I have seen.

Also thanks for the reference about the face hardened armor from Miles. I will admit while trying to read it, my eyes glazed over and I had a sudden urge to never look at a report again.

Rune

[rexford]

Originally posted by rune:

Thank you rexford...

The figures shown by rexford are still much lower then originally stated. I do not know where he got those figures, as they do not match anything I have seen.

Also thanks for the reference about the face hardened armor from Miles. I will admit while trying to read it, my eyes glazed over and I had a sudden urge to never look at a report again.

Rune

The 122mm AP penetration figures are homebrew, based on extrapolation from British and American AP rounds using nose hardness factors.

[rune]

Sorry should have been more clear, the figures provided by Rexford are 6-10 mm below what Reozil stated. Obviously I trust rexfords numbers...

Rune

[JasonC]

"122mm AP is not going 640 m/s at 2000m"

The original poster specified APBC. Was there a capped round for the 122mm?

Is your 560m/s at 2000m figure based on an uncapped round? Are the Russian battlefield sight numbers supposed to be for an uncapped round?

I would not believe only a 20% penetration drop between 500 and 2000m (as RB gives) for an uncapped round, but it would be a lot more believable if there are capped and uncapped versions, and you and RB are talking about 2 different rounds.

Pictures I've seen of BR-471 show a pretty sharp nose, not a blunt one.

I've seen the round referred to as "uncapped AP", also as APBC, as BR-471 and sometimes more specifically as BR-471B.

There is also the report of initial penetration difficulties with APHE that cleared up suddenly in the summer of 1944. The usual reading I've seen of that change is that German armor quality dropped, due to scarcity of alloying materials. But was there any change in the 122mm round?

Why do I sometimes see "471B" and sometimes just "471"? With other rounds, "B" tends to denote "capped".

[rexford]

BR-471 is uncapped 122mm AP, BR-471B is APBC for that gun.

Russian Battlefield penetration figures for BR-471 uncapped AP are based on 640 m/s velocity at 2000m, which is nonsense.

Originally posted by JasonC:

"122mm AP is not going 640 m/s at 2000m"

The original poster specified APBC. Was there a capped round for the 122mm?

Is your 560m/s at 2000m figure based on an uncapped round? Are the Russian battlefield sight numbers supposed to be for an uncapped round?

I would not believe only a 20% penetration drop between 500 and 2000m (as RB gives) for an uncapped round, but it would be a lot more believable if there are capped and uncapped versions, and you and RB are talking about 2 different rounds.

Pictures I've seen of BR-471 show a pretty sharp nose, not a blunt one.

I've seen the round referred to as "uncapped AP", also as APBC, as BR-471 and sometimes more specifically as BR-471B.

There is also the report of initial penetration difficulties with APHE that cleared up suddenly in the summer of 1944. The usual reading I've seen of that change is that German armor quality dropped, due to scarcity of alloying materials. But was there any change in the 122mm round?

Why do I sometimes see "471B" and sometimes just "471"? With other rounds, "B" tends to denote "capped".