The Engineering History of the M9’s Pivoting Locking Block

M9_DA-SN-91-11017As most of you know, the US 9mm Pistol M9 uses a pivoting block design, originally developed and patented in 1950 by engineer Tullio Marengoni of Beretta of Gardone, Val Trompia, Italy. But he drew, of course, on the 1936 design by engineers at Carl Walther Waffefabrik, then in Zella-Mehlis in the state of Thuringia, Germany, that would become the P-38 locking system. However, Walther’s designers, Fritz Walther himself and Fritz Barthelmnes, drew in turn upon earlier work by the Mauser-Werke’s Josef Nickl and Nickl’s own mentors, the three Feederle brothers. Thus does one feature of one famous firearm bear the stamp of not just one, but seven brilliant designers, each one of whom has passed on and each of whom is better known for other firearms!

There are actually more designers involved than that, because the Beretta M92/M9 has undergone quite a bit of engineering work in recent years, after production engineering “improvements” over the original M1951 materials and methods turned out to reliability engineering disasters; but the original M92/M9 locking block was very little altered from its M1951 forebear.

To tell the whole story, we must go back to the beginning of automatic pistols and the Feederle brothers, Friedrich, Fidel, and Josef, the developers of the Mauser 1896 pistol, the famous “broomhandle,” the first commercially successful self-loading automatic pistol. By 1907 they were working on a new design that involved a large pivoting block as shown in German Imperial Parent (D.R.P.) Nº. 209513. (The patent is in Paul Mauser’s name, as was normal in the Mauser-werke, but it was the Feederles’ work). The locking block of the experimental 1907 Mauser is large and located behind the breech face in the rear of a slide, but the way it pivots to lock the slide to the barrel during the short recoil is the first invention on the way to the M9’s locking system. But the Feederle brothers are certainly best-known for the C96, which used a different locking method entirely.

mauser_locking_block_patentA Feederle protégé brought the next innovation into the design when Bavarian engineer Josef Nickl began experimenting with breech locking. Nickl’s goal was to update the Mauser 1910/1914 pocket pistol to a more powerful cartridge like the 9mm Parabellum, and he tried many different kinds of locked-breech mechanism to make this work. At one time or another, he experimented with flap-locking ike a Degtyaryev machine gun, a rotating barrel like the Mexican Obregon, and the mechanism in which we’re interested in — a pivoting locking block that moves much like a Beretta locking block, but is mounted below the barrel. This patent — credited, as usual, to Paul Mauser — was DRP Nº. 250493 of February 5, 1911.


A prototype, serial number 4, survives and has passed through several top-flight collections, including Dr. Geoffrey Sturgess’s. The following Nickl prototype pistol will be in the RIA April auction. It’s in .45 caliber (one of several such Mauser-werke prototypes) and may be flap or pivoting-block locked (it’s not clear). It is marked with the serial number “2”.

mauser bretherton tipping block locked 2

The following is  9mm pistol, serial # 129, showing the “chipmunk cheeks” of the Nickl pistol using Degtyaryev locking-flaps. It too is in the RIA April auction.  mauser bretherton flap locked 2

Nickl, though, is not famous at all for his locking block, which is a footnote to Mauser’s efforts at best. He is best known today as the father of the first “native” Czechoslovak firearm, the Vzor (Model) 24 pistol, a barely-modified, badge-engineered version of one of his Mauser prototypes. Nickl offered it to the Czechoslovaks while installing a Mauser-built production line for rifles at the Zbrojovka Brno plant.

walther_locking_block_patentWhen the Walther firm developed a 9mm pistol bringing their double-action, single-action / safety-decocker concept to the service pistol, their design had three new patented features: the dual recoil springs, the hammer design, and — germane to our subject here — the locking block. While Fritz Walther, son of Carl whose name was on the letterhead, was involved in the design, the principal design seems to have been that of engineer Fritz Barthelmnes, then a Walther employee. According to Bruce’s excellent book, Walther’s name alone appears on the relevant German patent, DRP 721702, applied for 21 October 1936 and issued 15 June 1942, but Barthelmnes is actually also credited on the patent and on derivative foreign patents.


The key feature of the Walther block, missing from earlier versions, is the unlocking or disengaging pin that ensures positive unlocking of the block (#12 in the illustration above).

Barthelmnes is known, of course, for the P.38, but he’s arguably better known for his own postwar FB-Record blank and air pistols.

Which brings us to Italy and Tullio Marengoni. At a glance, Marengoni’s 1950 patent (Italian Patent Nº 467871) appears almost identical to the Walther patent. In fact, we were unable to get our hands on the Italian patent and see just what Marengoni is claiming that Walther and Barthelmnes didn’t in their 1936 patent — but it’s interesting that Marengoni does not cite the two Fritzes’ patent at all, according to the patent citation records at the German patent office. (This may be caused by the German database not seeing foreign patents). If we can get a hand on Marengoni’s patent, we’ll see if we can determine where his design differs from Walther’s (a diagram in Bruce’s book does show that one of the claims was the Beretta disconnector, quite different from a P.38’s).

So next time you check an M9 out of the arms room, take a good look at that block! You’re handling the best efforts of many of the world’s greatest firearms inventors, all the way back to the first auto pistols in the 19th Century.


Bruce, Gordon. The Evolution of Military Automatic Pistols: Self-Loading Pistol Designs of Two World Wars and the Men who Invented Them. Woonsocket, RI: Mowbray Publishing, 2012.

German Patent Information System Network (DEPATISNET). Various historical patent documents. Searched at and Retrieved from

12 thoughts on “The Engineering History of the M9’s Pivoting Locking Block

  1. Keith

    I have a 92FS and I’ve never had any issue’s with it. Bought in the 1994-97 time frame. Very good write up.

  2. DSM

    And a design that continued to be evolved in the case of the M9 as seen with the relief cuts and radiuses cut into the corners of the lugs. As I recall we saw the first of the updated blocks around the ’04-’05 timeframe but they may have been out before that as the stock of old parts dried up.
    For the bulk CATM sections in the AF they have training weapons assigned that most of the base populace use for qualification. This means they usually all have ridiculously high round counts. I’d spend half of my annual maintenance budget on blocks and barrels. After the upgraded block that number was cut considerably. I haven’t touched an issued M9 in years to know if it has evolved even further but it wouldn’t surprise me to hear it has.

    1. Miles

      There has been one more incremental change.
      The locking block ‘pin slot’ was narrowed and the pin thinned to match.
      What was really an interesting part of this was that the cost to change out the block and pin was only $6 less than the LOGSA price for a complete barrel assembly. So, you can guess what happens. Also interesting is that FN got a contract for the new barrels!

  3. Daniel E. Watters

    Back in October 2015, PS Magazine announced that another M9 slide separation with injuries had recently occurred. It seems that the pistol had never been upgraded with the slide-retaining hammer pin. Note that MWO 9-1005-317-30-10-1 for this modification had been issued all the way back in March 1989, with the expectation of completion by June 1993.

    More details are available in TACOM Safety of Use Message (SOUM) 15-011.

    1. Miles

      What that incident means is that; every time that pistol had an annual inspection, a multiplicity of smallarms repairers missed that item on the checklist.

      More simply: ?

      1. Kirk

        Not that hard to believe, actually. The number of people out in the units who are actually a.) qualified to do the job, and b.) interested in doing it? Vanishingly small.

        Alternatively, the pistol could have been in some backwater storage site, and the fix never got applied because of that. You would be amazed and bewildered at what can come tumbling out of the supply system at you, when push comes to shove. I had a brand-spanking new 1960s SACO-Maremont M60 handed to me out of war stocks, when I was in Germany back during the mid-1980s. Didn’t last too long, but it was brand-new, and without any of the numerous upgrades that gun should have received in the intervening years. From what we were told, it came out of the very first POMCUS stocks, that they were going through and cleaning out for some damn reason. Same time frame, we had literally tons of 1940s TNT and other demo stuff rain down on us for training…

        1. Miles

          But even if that particular pistol had come from some “Raiders of the Lost Ark” warehouse, there’s this thing called “service upon receipt”. Someone dropped the ball, not that that may actually mean anything past that SOUM.

          Oh well, it ain’t my problem now.

  4. DSM

    “What that incident means is that; every time that pistol had an annual inspection, a multiplicity of small arms repairers missed that item on the checklist.”

    Big time. Thing is the TCTO was so long ago that the bulk of gun plumbers have never seen an old hammer pin and the assembly line approach often applied to a mass inspection where everyone gets one gauge or task could’ve missed it easy. Efficiency, sure I’m all for it. How about reading the TO first, or the -23&P TM if you’re of the Army type, and having it there while you’re doing the task? I don’t care how many times you’ve done it, it doesn’t cost you a thing to do it correctly.

    I had the fear burnt in me early on when some 240s I had completely overhauled were used in a scuffle on a convoy. Yes, people depend on the work you do.

  5. staghounds

    I’d suggest the block is older than that, because it’s the spitting image of the little flap that keeps an 1886 Mannlicher straight pull rifle locked. I suspect that the Federle brothers were well aware of these rifles.

    The John Browning of Europe strikes again…

  6. vince

    Just an odd little side bar….the M9, when the brass is ejected, the casings bounce off the top of my head. About 1/3 of the time. This happens with no other pistol I’ve ever tried.

    Sorry for the drift….I just had to get that out of my system.


  7. Epk49

    You did not mention the Walther P5. It, too, uses the P38 design albeit with minor modifications.

    1. Hognose Post author

      Quite true. The P5 was used by the British Armed Forces to a limited extent. I further didn’t discuss the P4 which looks exactly like a P.38 at first glance, but has some interesting improvements. It was used by some German police agencies. These two firearms are definitely in the mainstream of Walther locking blocks. I think the P5 may still be available in Europe but it went out of the US catalog some years ago.

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