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Shop Tuesday 9-16 solid model the MP-44 trunnion

A friend of mine dropped me an e-mail wanting to know if I had drawings for the trunnion of a MP-44 and being a fanatic on engineered drawings I said yes. These are the same drawings that are all over the internet and they are wrong. So I decided to set down and make a correct solid model for him. Using the drawings as a starting point then I measured one as well as the parts that attach to them.

IMG_2455_s_w

IMG_2458_s_w

IMG_2456_sThis is a solid model that I did last Saturday on the trunnion.

MP-44 trunion4

MP-44 trunion3

MP-44 trunion2

MP-44 trunion1

MP-44 trunion5There are differences even between trunnions. Here are pictures of one in the rifle and one that has been removed from a rifle. You can see the differences just in the upper radius where the sheet metal attaches just below the gas tube. The first photo is one in the rifle.

DSC_0002_sw

DSC_0001_swThis is a different maker.

DSC_0003_swNotice the extended lips on the second picture verses the one still in the rifle.

In addition to drawing the part up a friend also did an analysis of the steel in the trunnion.

The specification for this part is C 0.45; P  0.044; S  0.039; Mn 0.62; Si 0.23; Ni 0.08

Hopefully after we finish the 10 projects that are on the mills now we can make a few for him.

As always comments and opinions are appreciated.

14 comments to Shop Tuesday 9-16 solid model the MP-44 trunnion

  • John D.

    Silicon killed DIN C45 steel. Essentially a low end manganese AISI/SAE 1045 steel without the modern aluminum addition.

    Usually quench and temper heat treated, not carburized.

  • JB

    Are MP44 trunnions case hardened?

    Do you know if this was a common alloy for gun parts?

    my knowledge of WW2 German steel alloys is nonexistent,how dose this grade compare with say SAE4140 in this application?

    • John D.

      Not case hardened (carburized, nitrided). Case hardening is only effective on lower carbon steels, such as AISI/SAE 1018. Steels with more than about 0.25% carbon become quite brittle when carburized. AISI/SAE 4140 is a 0.40% carbon, chromium-molybdenum alloy steel which is quench and temper hardened in much the same way as the DIN C45 here, although I am not certain that the MP.44 trunnion was hardened.

      As the war ended, German weapon manufacturers and their subcontractors began to encounter a lot of supply and equipment maintenance disruptions. The high sulphur and phosphorous content of this trunnion’s steel suggests that it was made from late war steel, after the German steel mills encountered limestone shortages. Heat treating operations were most frequently affected at parts manufacturers because they required erdgas synthesized from coal. The Waffen Amts frequently authorized the use of unhardened parts with little testing on simple firearms such as the MP.44.

      The MP.44 trunnions would by about 90 Rockwell ‘B’ hardness as forged, depending upon whether the forgings were normalized. Quench and temper heat treating of C45 is usually targeted at a 28 – 32 Rockwell ‘C’ hardness range in weapons parts, just a little lower than AISI/SAE 4140 parts in modern firearms.

      • JB

        Thanks for the information John.

        Being that some trunnions are that soft excessive headspace would develop before to long right? or is the 7.92×33 to mild a cartridge for that?

  • All of the MP44 trunnions that I have seen were cheap steel. The trunnion retains the barrel and bolt at lockup and gets a lot of its strength from the barrel, bolt and sheet metal wrapped/spot welded to it. The gun was made to be a throw away weapon and only minor repairs were to made on it. The differences in production and quality of material between the MP43/1 made in early 44 and Stgw/MP44 made in Feb 45 are great but they both do the job for they were designed for. Harry

  • Will Cushman

    The expertese of Gun Lab readers is always impr,essive.

    • The more I chat with the readers and posters the more I learn. Had a great conversation today with a gentleman concerning pressings and the steel used for pressing. After chatting with him I realize just how much I do not know. All I have to say is THANKS.

  • Pete F.

    Would you guys think “brake die” 4140 to be a good material to make MP44 rec. blocks (trunions)from or would that material be overkill with some other steel being a better choice?
    Thinking something not needing post machining heat treat would be most desirable.
    The original ones I have Rockwelled punch in the low 20’s. Softer than one would think!
    Pete in St. Louis

  • S.N.A.L

    where did you find the blueprints ?

    i found some blueprints of the mp 44, but they are poor quality scans .

    same question for your Gerat 06 and your Gerat 05.

    • Most of the work was performed by reverse engineering original weapons or parts. Not all of it by me. There are a great number of people working toward making the final project.

  • juver

    i too have seen the poor quality scanned blueprints of the mp44
    do you have or know were i can get a better version of this

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