The M1A2 that could have been, L55 120mm main gun

Would be an easy and eye catching conversion of an iconic MBT.

Thanks to TankPorn for the images.

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As being a M1A1 tanker and a model builder of armor, i did just that. I took the 120mm main gun from Leopard 2A7 with that 120mm on Trumpeter’s M1A2SepV2. Photos to follow. The paint scheme is the new active army two tone green.

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I meant Rye Field not Trumpeter. Oops

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That’s a 1998 document. At the time, we (the US Armor community) thought that only a longer gun would get us the KE necessary to defeat foreseeable enemy designs.

Fast forward 25 years. The real success story of the American tank development process found a much simpler way: ammunition development.

The original M829 APFSDS was hustling a 627mm LRP (long rod penetrator) along at a muzzle velocity (MV) of 1670 m/sec. It could penetrate only 540mm of RHAe at 2,000 m. It was chunky too, as its L/D (length over diameter) ratio was about 23:1.

Subsequent re-engineering has lengthened the M829A3 to something like this:

This new M829A4 round is now slow(er): the LRP is a bit longer at 770mm long (two-pieces now) and it has a MV of 1,650 m/sec. The L/D is now 37:1, and the perforation is cited by unclassified sources as > 980mm RHAe. These data generate 12 MJ of KE at 1,550 m/sec. Compare that to only 5.94 MJ of KE for the M829. Improved powders also shoot cooler while attaining the optimal velocity necessary to perforate that deeply.

The reason the Rh-120 is now L/55 is because the Germans choose not to use DU LRPs. The use of WHA (tungsten) LRPs requires higher velocities to achieve perforations equivalent to the M829A4.

The Russians still have a bazillion of the early steel LRPs. Have you noticed their 125mm tubes are L/48 at 6 m of length.

The L/44 M256 is only 5.3 m long. That has some useful advantage in fighting.

The Rh-120 L/55 is 6.6 m long! Yikes!!

Here is a plot of the science that depicts the rationale for the longer barrel Rh-120, and the velocities needed to defeat a target of a certain Brinnell Hardness.

Do note that this data is several years old, and the developers (Willie Odermatt et al) normalized all KE to a single value to demonstrate the physics. The L/D is also fixed at 30:1.

Today’s DU M829A4 LRP is a marvel of science, designed in such a way as to allow continued use of the L/44 120mm at reasonable velocities and gun tube wear. And lethality out to about 4,000 m against known or likely MBT threats.

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Matt-
I’d love to see that new two-tone ODG.

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