Wednesday, February 10, 2016

M829A3 APFSDS penetration power - common internet estimation failures?

The M829A3 is currently the latest type of APFSDS ammo in service with the United States armed forces. It replaced the M829A2 in 2003.
In the next year(s) the M829A4 will take over the place of the M829A3. It is already confirmed to have the same exterior dimension and general characterisitics as the M829A3, but utilize an improved penetrator designed to penetrate even newer types of ERA ("3rd Generation Explosive Reactive Armor").
The M829A3 APFSDS of the US Army
In order to estimate the penetration power of APFSDS different mathematical fomulas can be used, such as the formula developed by Lanz and Odermatt for the Swiss military procurment agency. This formula has gained most acception in also mentioned in different documents of the US Army Research Laboratoy. It is an empiric forumla, which means it's a mathmatical interpolation of actual tests results in dependence of the changed parameters (density, length, diameter, etc.).

The M829E4 is confirmed to have the same dimensions as the M829A3
On different forums such as Tank-Net, the WoT forums and for different software, such as the Steelbeasts simulator/game from eSim Games, people have tried to calculate/estimate the penetration power of the M829A3 APFSDS based on measurements on photographs and available data from the manufacturer's website.
However most of these people are assuming a penetrator length of 780 mm to sometimes even above 800 mm! This is solely based on the increased length of the in-flight projecitle and the assumption that the M829A3 uses a "stepped" tip assembly like the M829A2 APFSDS. This way, the estimated penetration of the M829A3 APFSDS from the 44-calibre long M256 gun against rolled homogenous steel (RHS) reaches or even exceeds the penetration of other types of ammunition fired from the longer Rheinmetall L/55 gun. Penetration values above 750 mm into RHS after 2 kilometres are commonly estimated for the M829A3.
Does the M829A3 possibly look like this?

However patents from Alliant Techsystems (ATK) show us a different possibility of the M829A3 design: instead of utilizing an elongated DU penetrator with conventional tip to defeat tanks fitted with heavy ERA by "brute force", it is suggested to use a special tip assembly to overcome ERA. The tip is a solid steel construction with a length "greater than 100 mm", while the main penetrator has a length of "about 630 mm, preferably greater than about 650 mm, and more preferably greater than about 670 mm". Specifically the last value is interesting, because this is very close to the reported length of the penetrators used in the previous M829A1 and M829A2 APFSDS rounds. Furthermore the thickness of the rod was increased from 22 to 25 mm, which result in a 67% higher bending stiffness (and thus better performance against ERA).
Such a penetrator design has a big benefit against targets protected by heavy ERA, which is what the main target of the M829A3 development was. The solid steel tip will punch a hole into the ERA, but is designed with a special weakpoint at the connection to the main penetrator; it will break of instead of transfering the stress created by the interaction with the ERA-plates onto the main penetrator. While the M829A1 was unable to defeat the contemporary Soviet tanks with Kontakt-5 heavy ERA, the M829A2 was designed as "brute force" solution against Kontakt-5 armed Soviet tanks. The M829A3 was the "elegant way" to defeat better armored tanks with Kontakt-5 or the follow-up ERA.

There are further reasons to assume that the M829A3 APFSDS follows the above mentioned design:
Unlike it's three direct predecessors, no M829A3 cut-through model has ever been displayed, while cut-through models of the earlier APFSDS types were presented while they were the latest stuff the US Army had. 
Furthermore there is the weight growth of the M829A3 compared to the M829A2. While the sabot material was changed - an improved compostion reduced the density - the overall sabot weight of the M829A3 is understood to be higher to due the much longer sabot petals. Values from the US laboratories responsible for developing/manufacturing (composite) sabots for the M829 series show that the sabot weight of the M829A3 should be 3 kilograms and that of the M829A2 should be about 2.4 kg. A 780 milimetre long DU rod with 25 mm diameter will already weigh 7.08 kg and thus be a contradiction to the 10.0 kg weight for the complete projectile assembly from ATK's brochures. A rod with a length of about 680 mm and a 25 mm diameter made from DU  however will weigh about 6.18 kg and thus leave about 0.6 kg for tracer, fin assembly and the 100 mm steel tip. Given that a 100 mm steel rod with 25 mm diameter weighs about 400 grams, assuming that the M829A3 uses a 680 mm DU rod with 100 mm steel tip seems to be very reasonable based on the weight.

The US Army had no problems showcasing a cut-through M829A2
What impact does this have on the penetration estimates mentioned earlier? According to the patents from ATK, such a design increases the penetration into RHS protected by an unkown type of heavy ERA by 20 to 30% compared to the same penetrator without solid steel tip. Against normal RHS not protected by any form of ERA however the penetration increased only by 5 to 10%, which is to be expected due to the steel tip also prodividing penetration.
The M829A3 might as well be optimized for fighting tanks with heavy ERA such as the main tanks of all potential enemies of the US/NATO - China, Russia, North Korea all utilize heavy ERA on their latest tanks. So instead of having some mind-boggling penetration (for an APFSDS fired with the short L/44 barrel) against all types of armor, the penetration against RHS/composite armor might be as low as ~660 to 700 mm; enough to defeat the main armor of tanks like the T-80U, T-90 and Type 99.
Penetration of APFSDS with steel tip vs conventional tip

5 comments:

  1. Er how can there be no "cut through" model of the M829A3 displayed when the first photo shows some sort of image of it?

    Then there's stuff like this as well: http://i.imgur.com/yUmLAZu.jpg

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    1. Well, there is a semantic difference here. What is shown in the photograph above is a cut through "projectile assembly" consisting of a propellant charge case, a sabot and the projectile. The projectile however is just the "dart"/"arrow", which is held partly inside the propellant charge case by the sabot. The projectile is not "cut through", but untouched in the photograph used in above article aswell as in the photo compilation posted by you.

      You can see in the photo compilation posted by you, that the penetrator of the M829 and M829A3 are not shown, the projectiles of these rounds are complete. On the M829A1 and M829A2 the projectile is also "cut through" revealing the dense DU penetrator embedded inside the projectile. You can see that at the tips of the projectiles.

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