Musket to Big-Bore Rimfire: the Roberts Short-Frame Conversion

Brigadier General Benjamin Stone Roberts designed and patented a fall-block style of breech loading conversion to .58 Rimfire. Over the course of the decade after the Civil War, he was able to sell approximately 23,000 of these conversions. The work was done by the Providence Tool Company, and included two main patterns – the early short frame and the later long frame. This example is a short frame gun, probably from a 5,000-gun contract to Brazil.


  1. I wonder if the complaints about the rifle were more about the action or the ballistics & recoil of the cartridge? Be fun to find a Mexican one & line the bbl for .44-40 or .45 Colt. Beautifully simple conversion.

    • . . . along with hundreds of thousands of other surplus and ‘conversion’ firearms made in US factories under Civil War contracts, from rifle-muskets through Sharps and Spencer carbines and rifles, during the Franco-Prussian War of 1870~1871 when France was in dire need of reasonably modern firearms, being unable to keep up with the demand for Chassepots in the face of massive losses.
      Your point?

  2. Coming up with a design for a good muzzle-feeder-to-cartridge conversion is an enjoyable diversion to this day. It’s not so easy if you put yourself in the place of an inventor who knows that many armies in, say, 1867, insisted on visible hammers (did that make range drill easier? damfino) and rather implausible strength tests.

    Roberts did a pretty good job with his design. If we pretend that he offered his iron in a carbine version and a caliber like .45 long colt, it would make a dandy modern replica.

  3. Probably needs a wee stud, further forward on the falling block; that the hammer could cover when fully forward… But not on half cock, when it could function as now; seemed to open quite easily with the hammer fully down.

  4. I have been “Wittering” on about hand held (locks) delay devices lately; and I think if this had a “Pauly 1812” type spur emanating from the hook latch… Down to the “pistol” grip, I think your thumb would have aided it’s function: As an example, via gripping the gun.

    Resulting in the Brazillians perhaps complaining less.

    Now prior I said another stud and half cock, and am saying that is better if possible. But I have watched this video alot now, and er… There is a noticble issue with that action, the bolt opens to easy with the hammer down to easy (Think recoil) it is almost; an accidental semi auto Pederson type inline bolt, which in this instance failed. As probably… Not intended. Or was it? Interesting thought, albeit it still failed.

    Otherwise that bolt is just plain wrong (I like conversions and appreciate the simplicty, dual function of parts etc)

    Interesting gun.

    • The rear of the case head would fail etc; as the author said. Just an odd action that, sure the other ones used the hammer “As a lock” hammer down…

      • When I say semi auto, I mean you pull the trigger; hammer falls, BANG!!! Right… Then it just opens & auto ejects I.e. The point.

        Which did not work so good in practice.

        • I am saying it was that “You can hear it in Ians voice, he knows what he just said is problematic.” it is an attempt at auto eject; were is that Russian person who likes to flirt with me, with his patents.

          An attempt which would have been made better, with my manual handling idea I.e. The spur & grip; which is what I have been waffling about for a while this is the perfect potential example.

          The grip, your grip; would have enabled it to auto eject, slowly enough.

  5. That is all I meant with the Fg42 etc, waffle. I meant this; if you can’t see this now… I may actually have to call you stupid and fall out accordingly.

    Or, I want somebody to spell out why I am wrong. This is fair enough, I have been posting on here for nearly a decade and have learnt lots. “Tons infact, tons.”

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