1/16 RC US 155mm Gun Motor Carriage M12 - Build

[lmcq11]

Hi everyone,

This will be my build for the next couple of months, a WW2 US Self-Propelled 155mm Howitzer, the M12 Gun Motor Carriage.

Based on the M3 Grant chassis, 100 of these were built in 1942-43, with 74 later being overhauled and sent to Europe. Meant as an SP Howitzer able to follow the advance of the mechanized forces, it was sarcastically nicknamed "Doorknocker" thanks for its ability to pierce 7 feet of concrete in direct fire role, very useful against bunkers of the Siegfried line.

The main objective of the RC build is to provide the highly sought sliding breech recoil seen below, with some elevation, prioritizing these over gun horizontal movement, similar to what i did with the Hummel build. I will have to see what can be achieve here.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

Graph of the M12, showing its updated M4 bogies suspension and its WW1 era French designed 155mm gun.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

The M12 was designed to provide indirect fire support. It has no crew protection other than the driver and radio crew at the front. Seen here with poles for use of a rain tarp for the rear compartment.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

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Shown here in dramatic direct fire support on the front line. It shows a very long sliding breech recoil. A solution will have to be found to achieve this although i will likely have to reduce expectations as to the length of the recoil that can be achieved. The usual 15mm or so of recoil won't do...

1/16 RC US 155mm Gun Motor Carriage M12 - Build

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1/16 RC US 155mm Gun Motor Carriage M12 - Build

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A colorized view of an M12, seen on the web, with a good view of the rear blade. The model will need to feature a mechanism to lower and raise the rear blade.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

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The conversion will be achieved with the help of the Vandra M12 GMC conversion kit for the M4 Sherman hull. At first sight, it looked pretty good.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

For the build, i will be helped by the Academy M12 1/35 kit for parts dimensions, placement of items and to help me fill the gaps.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

I have lots of experience with Vandra kits. First thing to do is to analyse the kit, compare parts against references and see what we are dealing with. First part looked at is the base of the howitzer. Bad start, it shows the diameter is undersized by a whooping 10mm against the Academy kit part when extrapolated to 1/16 scale. Knowing my history with Vandra kits, i think the Academy kit is likely the one that is accurate. Will see later if it can be fixed somehow.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

Looking at the barrel and cradle, i am happy to see that it is not molded as one single piece. The barrel is independent and can be made to recoil.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

Continuing on following post

[lmcq11]

View of the cradle (uncleaned) and the misaligned rail under the barrel. This will need to be redone for a more strait and solid integration, allowing for a strong servo recoil.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

Compared to the Academy kit, the cradle has some shape and design issues impacting the width, and is missing 4mm in length.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

The breech is missing 2.5mm in diameter.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

At first sight, the barrel seemed too thin. Overall length is missing 10mm. When comparing to the Academy kit, the last section at the breech is missing 4.7mm in diameter, which is quite a lot. I'll see if something can be done about it by adding overlaid tubing to the barrel to help bridge the gap. My guess is that this will also impacts the cradle width. The tip of the barrel is missing 2mm in diameter. This is sad because the gun barrel should be the highlight of this kit, and it seems to have major issues compared to the 1/35 kit. Fixing this will be tough. It might not bother some builders who are just looking for a basic representation of the M12, but it does bother a rivet counter like me a lot.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

The resin barrel as a metal tube inside, which is good. However, the tip of the metal tube is badly inserted into the resin and it shows a sideways exit.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

The upper hull body is adapted to fit the Heng Long M4 Sherman hull. It shown some dimensional issues by a few mm but looks ok otherwise. What is annoying is the use by Vandra of double diamond pattern thread plates, it should be a single diamond pattern. This will need to be fixed.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

Comparing Academy and Vandra shaped for the front section. Notice the difference in angle between the two.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

Instead of using a Heng Long M4A3 Sherman chassis with the bogies that have a large hole in them, a design feature that i truly hate, i will instead use a Mato plastic M4A1 hull purchased with Mato points on MatoMart.com, and cleaned up of all features.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

Mato metal bogies on inventory will be used, looking good. Its just too bad that they could not put realistic markings on them instead of the garbage they put on.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

The square edges of the rubber rim will need sanding to make them more round, and look worn.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

continuing on following post.

[lmcq11]

Mato Sherman metal track adjusters with more accurate replacement idler wheels will be used.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

I had a set of Taigen Sherman T48 metal tracks with matching closed (plated) teeth sprockets on inventory, unused from a past build. The M12 in wartime pictures show that all the most common types of Sherman tracks were used, including the T48, with closed teeth sprockets, not the one with open (hollow) teeth sprockets.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

These tracks have a single working pin, the other pin is represented by molded on connectors to the pad. They also have some accuracy issues. Not ideal but this M12 is a good way to finally used them.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

I do not plan to spend a lot for a fancy gearbox for this build. I have an older Heng Long gearbox on inventory, looks like a good way to use it if i can keep the speed under control with the board.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

There are really few references available on the m12. The only book i have seen is this one from David Doyle. Recent, it contains good wartime pictures, and a good walk around section with lots of pictures of the only surviving M12. Otherwise, the book is pretty dry, mostly limited to technical descriptions and does not make a very interesting reading unless you are building an M12.

1/16 RC US 155mm Gun Motor Carriage M12 - Build

That's it for now. The build will start with the lower hull.

Regards, Louis

[Herr Dr. Professor]

Your a AFV-building machine, Louis. Oh, wow! Here we go again!

[PainlessWolf]

Good Evening, my Friend,
Looking very much forward to this unusual Build. Well in hand as always at the Start. Following along,
regards,
Painless

[tankme]

Cool project. No surprise the Vandra kit is off. Not sure if any of their kits are really very accurate.

[Manu-Military]

I can only but wonder why somebody is still trying to do anything with the vandra kits.
I had their M3 Lee which is a total load of crap and by seeing on their website their other kits, it's obvious they do look odd.

[Rob1970]

Looks like another nice one, I will be following this. Too bad the Vandra kit seem to disappoint (again). I had kinda hoped to pick one up at some point, but from reading the first posts I might go for scratchbuilding like I did with the Lee/Grant after seeing the errors in that kit. I mean, a difference of 20mm in the turret diameter alone? .

[Kaczor]

Looks like another fantastic project. Pity that base kit is lacking in accuaracy again.

[lmcq11]

Thanks everyone for the encouragements.

I can only but wonder why somebody is still trying to do anything with the vandra kits.
I had their M3 Lee which is a total load of crap and by seeing on their website their other kits, it's obvious they do look odd.

Yeah, i think this sums up the situation. Vandra obviously design their kits by eyeballing some pictures and are satisfied with how it ends up coming together. The M12 is not the worst i have seen but i was hoping that the gun barrel would be better. It is an added challenge to take such inaccurate conversion kit and do something better with it. It's what i do as a hobby. I see them like a basic kits, and i never follow instructions. With some scratch building and no real alternatives available, the Vandra bases can usually be turned into good looking models. You just need to put on your Dr. Frankenstein hat; crack open the hull, tear into the internals, cut the fat, replace some body parts, add on extras, and put back together what remains with superglue. It's actually fun to do once you got over the initial shock that this will not be a simple kit. I did a few of Vandra's conversions, They can be turned into unique models. I would not have these models without Vandra;

The M7 Priest with reworked hull and new interior;

1/16 RC M7 Priest

1/16 RC M7 Priest

1/16 RC M7 Priest

The M3 Lee with reworked hull and scratch built turret

1/16 RC M3 Lee

The RAM II tank, with lots of cutting and downsizing.

1/16 RC RAM II

When i am done with the M12, i am pretty sure it will look good.