Prototype Dieckmann P66 Pistol at RIA

The P66 was a prototype .22LR semiauto pistol designed by a German immigrant to the United States by the name of Rolf Dieckmann. It never went into production, but had a number of interesting features, including a removable firing mechanism and a combination extractor and firing pin. In addition to Dieckmann pistol number X3, this auction lot also includes number X4, a cutaway model.


  1. Interesting pistol, I’d buy the pair if I was a Yank and had some spare cash.

    You could turn that magazine idea into a sort of grip safety perhaps i.e. Have the magazine pivot, in a fashion… Against a spring loaded cam type thing, thus the magazine would only be in the correct position for firing when you squeezed the grip therefore pushing the rear of the mag into the pistol grip.

  2. The magazine is interesting feature. I am wondering does it affects reliability to noticeable degree? I am thinking why .22 rimfire so don’t “like” box magazines, it is because: it is rimmed? or it is outside lubricated (i.e. the smaller force is needed to separate bullet from case than in inside lubricated cartridge like .22WMR)? or it as a default use LRN bullet which can not be used to set cartridge properly during ramming into chamber like FMJ bullet?

    • There are two aspects to the problem

      firstly, you need to have the rims correctly aligned to avoid them interfering and stopping the top round from stripping.

      secondly, you need to be able to transfer the spring pressure up to the bullet of the top round, in order to prevent it from nose diving when it tries to feed

      a curved single stack magazine addresses both of those problems, as each round in the magazine contacts its neighbours at both ends

      preventing the rims from moving to a different position from that in which they were fed, and holding the bullet of the top round up in the feed lips, for correct feeding

        • You have two and a half options for getting contact between the back and front of tapered or rimmed cartridges through the whole stack in a box magazine

          The half option is to use a follower which can tilt to take up the slack, as in most centrefire bolt action rifle mags.

          the two proper solutions are, curve the magazine to accomodate the taper or rim of the cases.

          or, have the mag wider at the back, so that the cases stagger slightly more to their rear, in order to accomodate the taper.

          IMHO one of the best mag designs with respect to giving attention to reliable feeding, was Patchett’s roller follower, banana shaped mag for the Sterling SMG.

          Though straight stick mags may have been much more convenient for carrying around.

  3. I’m very dubious about the combined firing pin and extractor

    although a .22 RF will often work without an extractor (some, for example the Marlin, Gevarm, Voere etc open bolt .22 rifles don’t even have extractors, and unloading can be accomplished with a simple sheet metal piece on the barrel face)

    the idea of the extractor getting banged forward on every shot, and of it having free play before it hits a solid stop on every extraction, just seems to be asking for it to break.

    There are some interesting interactions between extractors and floating strikers in one or two centre fire rifles, for example one of the Voere bolt action rifles had a floating firing pin which was cammed into contact with the primer by the extractor, thus fractionally lightening the moving part of the striker to speed lock time, while avoiding the increased weight, spongy striker blow and propensity to break shown by the Krag and the 1903 Springfield, which copied the Krag’s appalling two piece striker (and the ridiculous heavy knob on its rear end too).

  4. Interesting design, but in many ways seems to be a solution in search of a problem. I agree with Keith that the combination firing pin/extractor seems to be a weak point of the design. Also, while novel in its concept, I think this pistol would require a significantly different manual of arms to facilitate reloading, creating problems with magazine changes by having to loosen and alter the strong hand grip on the frame in order to remove the empty, then re-insert a loaded magazine. Although reload speed would not likely be an issue with a hunting/target pistol, I could see this resulting in the pistol getting dropped frequently during reloads as opposed to the more common base/heel method of magazine loading and removal, which is second nature to anyone who operates a self-loading pistol. While potentially more reliable (at least in theory), I’ve put tens of thousands of rounds (or more) through my High Standards, Rugers, and my S&W 41s without any noticeable reliability issues regarding the more conventional magazine arrangement. That being said, it would be a nice addition to the collection from a standpoint of novelty and rarity. One cannot fault Herr Dieckmann for trying something different, though.

  5. One benefit of that magazine arrangement in a pistol, is the chamber can be located further back. If you look at it, with a “straight” magazine, tilted at that grip angle, the chamber would need to be a fair distance forward. There’s enough barrel inside the telescopic bolt, for a short barreled pistol.

    • You could remove the barrel, forward of the “receiver” section, and simply have a thread for a silencer and have a longer barrel in a shorter pistol than usual.

      • oooh, I really like this pistol the more I look at it… It’s saying “.455 Webley, make me a locking mechanism, I’m made for it, you can fit a bayonet”

        • A Pedersen “hesitation” lock, inside the slide within the receiver, might be apt with a low pressure cartridge, the .455 Webley is such a cartridge… Is it? He he. Fit six in there! Or if not, a variant of it… Lewis gun clockwork spring fitted below the magazine in the grip, the magazine is spring’less, but has a cutout on it’s underside… Hmmm, push mag in to tension spring… Tensioned bit, engages cartridge via a “follower” which fits, into the magazines cut out, pressuring the lowest cartridge in magazine appropriately.

        • ooh, ooh! A static barreled Luger design… A toggle lock, like off a luger, but actuated by the slide via gas ports from the barrel sitting in front of it, the thumb/finger circular grip things on the toggle ride up grooves cut through the receiver when the angled part of the slide hits the bar running between them, toggle opens does it’s thing, slide returns.

        • The Boberg feed system is virtually a copy of that in the Gabbett Fairfax Mars long-recoil pistol of a century ago;

          It was necessary in the Mars precisely because it was a long-recoil action. In many respects, it worked like a QF gun recoil system scaled down to pistol size; the feed system was necessary to allow the action to be far enough “back” to allow it to be held with one hand without excessive “nose weight”.

          In the end, it was academic; the tremendous recoil of the Mars rounds, notably the bottle-necked .45, tended to throw the gun right back over the shooter’s shoulder, with or without his gun hand still “attached”.

          Exactly what it accomplishes in a short-recoil design like the Boberg is difficult to discern. Some increased barrel length, yes, but not enough to make much of a difference in velocity of accuracy.

          Overall, it looks like a Glock with some unnecessary complications added. Accent on the “unnecessary” part.



  6. The philosophy of this design is questionable. The firing pin and extractor unit and Tokarev like hammer housing seems for providing simplicity whereas magazine attachment and takedown style seeming hard to make and intriquating. An expensive layout for a plinker or hunting pistol and, though a solid, unrecoiling, long sight radius, clumsy and heavy trigger/sear connection for a target handgun. A different concept for a firearm genius should think, but not an attractive construction for a manufacturer.

    • Externally it looks similar to Korobov TKB-022 rifle:
      but with less radical way of spending cartridge case (TKB-022 throws cases forward, through pipe over barrel, see pictures in link) and place of magazine (TKB-022 was designed to have good barrel-to-overall length ratio).
      In terms of geometry TKB-011M is similar to earlier Korobov rifle: TKB-408.

      • Thanks Daweo

        The Korovov looks very interesting. I wonder whether the annular gas piston suffered from the same problems which the Germans experienced, or whether this later development (no doubt with some post war work from German engineers in exile) overcame those problems?

        Falling or tilting (martini and madsen style) blocks seem to be something of a lost paradigm, they certainly have numerous advantages over the current paradigm of axially sliding breech mechanisms

        but likely also have all sorts of forgotten about and perhaps even some still to be discovered nasty disadvantages and engineering problems.

  7. .22 Hornet, that’s another potential advantage gained by this mag design, long cartridges, in a pistol your making each one go up a bit rather than across sort of thing, I think.

    • .22 hornet is not a good pistol round.

      To get sufficeint expansion ratio to make use of the available powder capacity at reasonable pressures, you need a much longer barrel (well over 12 inches)

      Overall length is too great for a mag in a pistol grip (I think the Remington fireball rounds were inspired by the hornet – they share the same case length), and in a revolver, the tapered case results in fired cases setting back and jamming against the recoil shield, and preventing cylinder rotation.

      Although it’s a lovely quiet round in a rifle, muzzle blast in shorter barrels is supposed to be absolutely atrocious.

      Even .30 Carbine (similar capacity in a straight sided case and with a 2.5 times heavier bullet) is a nasty little sod in a pistol.

  8. Most of the hornet wildcats seem to be set up for TC contender size pistols.

    There’s little if anything to be gained from a case longer than about 1.25″ in a pistol (Hornet is 1,4″)

    A hornet will open up, With some forming work and rim thinning and back chamfering of the rim, you can form the various .297/.230 short and long morris rounds (they were used in sub calibre indoor training adaptors for .577/.450 Martini rifles) and .297/.250 rook – a lovely little small game round from around 1900.

    The maximum a hornet will open up to is around .270, which might be interesting with heavy bullets out of a contender style pistol or out of a little rifle, giving a whisper type performance.

    But out of a pistol sized pistol – it wont do anything that can’t be done better by a .32 H&R mag or cheaper by a .22 rim fire of one sort or another.

    There are various PDW rounds which fire small calibre bullets very fast, the 5.7 FN round, bears a remarkable resemblance to the .22 / .30 carbine AKA .22 Johnson Spitfire from the 1950s.

    There is also the .256 win Mag (based on a necked down .357 Mag case) which gave very PDW like performance in the Universal Ferret – a little, .30 carbine derived rifle

  9. Hey Ian,

    in the video you reference some literature of Dieckmann’s.
    I’ve been looking for writing of his but can’t seem to find any, think you can point me in the right direction?

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