Centaure Infamous “Mystery” Conversion

# What is a Colt “Mystery” Conversion?

# Progress Report

# The PITA

# 1st Meeting of the FROCS 2010 & the Tiny Little Details


What is a Colt “Mystery” Conversion?

Who needs a model 1860 conversion cross between an army barrel with cool looking barrel lug of 1861 Navy conversion profile, on which a Richards-Mason type ejector housing is mounted with dimensions that differ significantly from the RM Armies assembled in Hartford during the 1870s, and a RM cylinder and frame assembly with a narrow “saddle”-type conversion ring for good measure?

RNMA #11691 1st variation 2nd sub-variation from 1972 (left), Colt 1860 Army “Mystery“ Conversion (right)

Exactly, every red blooded cowboy or cowgirl should have one or better still a pair. Because less than a dozen only are known from yesteryear, probably made South of the border in Mexico ca. 1875. At least that is the considered opinion of the late R. Bruce McDowell in his famous conversion bible A STUDY OF COLT CONVERSIONS AND OTHER PERCUSSION REVOLVERS.

Original “Mysteries” were made for the venerable .44 Colt center fire cartridge!

When Karl Nedbal phoned December 31, 2008 with an update on the Centaure Richards-Mason conversion we agreed that this was going to be the next project.

Above left 1972 production run of the mill RNMA #11691 was the designated candidate for this somewhat exotic conversion. The project was formally kicked-off April 30, 2009, the day the Richards-Mason came home.

Centaure "Mstery" Conversion

Project Outline

Base pistols

RNMA 1st variation 2nd sub-variation #11691


8", lug with 1861 Navy profile

Barrel marking



.44 Colt inside lubed (liner, .429 rifling groove diameter)

Ejector housing

Richards-Mason type


altered to Civilian type closing notches for shoulder stock in recoil shield



Conversion ring

gated, Richards III type

Conversion cylinder

newly lathed conversion type, Centaure proprietary naval scene engraved


altered C&B type from Centaure

Gate spring



Centaure (steel, with cut for stock)


Centaure (brass)


barrel, cylinder, back-strap rust blued, original case colored parts unchanged


Progess Report

It was also agreed that Karl would not dash ahead at his usual pace of three months for the completion of a conversion, but take his time with the Mystery project. So, he took his time studying whatever he could find to read about the “Mysteries”. In Fall he started working metal. Here is what we have November 9, 2009, see pictures below. Nedbal had

# reshaped the 1960 Army percussion barrel lug like one of a Colt 1861 Navy Richards-Mason conversion,

# plugged the slot for the loading lever in the barrel lug,

# installed the Richards-Mason type ejector housing.

# Although the “S” line on both sides of the lug is now more pronounced in true 1860 Colt-fashion no harm was done to the Liège Proof house acceptance marks on its left side during this operation (below picture),

# he removed the famous “Centaure step” where frame and barrel lug are meeting.

# For the “Mystery” Nedbal left the Belgian factory arbor in place but

# opened the right side of the recoil shield wide to make room for the internal spring loaded gate of general RM Navy 1861 outline, just a mite larger.

# For a period correct installation of the Richards III type conversion ring of “saddle” design the master will have to attach it to the recoil shield by a screw. This required working on the two notches for the shoulder stock and welding them shut. He then contoured and finished that area to shape. Now this is no longer an RNMA frame …

but this little operation transformed it into a Civilian frame, see above. Neat little job, isn’t it?

Regarding the finish of the Mystery conversion we have a change of the original plan which called for nickel plating like many of the originals. After my shooting experience with the Centaure Richards-Mason, however, it is going to be Nedbal’s traditional rust blue. He will make every effort to maintain the pretty factory case colors of the frame.

November 14, 2009: the loading gate is shaped and installed.

Please note the important tiny details of the “Mystery’s” conversion ring: it has this enlarged section at its base to straddle the frame. It flares out on both sides where it meets the frame.

Conversion ring straddling the frame (left), new conversion cylinder lathed, ratchets cut (right)

December 3, 2009 and the beat goes on: Nedbal is approaching completion of the “Mystery” conversion. By now the conversion cylinder is already milled to specs. But Nedbal had to remove a small layer of steel from the forward area of the frame…because for reasons unknown Fabriques d’Armes Unies de Liège (FAUL) had lathed the original C&B cylinder of #11691 with a diameter that is ca. 1 mm less than what is the norm (!), and had adjusted the position of the arbor in the recoil shield accordingly. In other words the overall height of the barrel lug is smaller than those of other Centaures.

Conversion cylinder installed, note slot on the right sight of barrel for ejector housing



Dec. 7, 2009 more news from the “Mystery” front: the cylinder is completely done now but this #11691 is turning into a glorious PITA. The technician back then at FAUL’s had cut the slot for the hand in the recoil shield too far off center compared to original Colts and other Centaures. Therefore, it will engage only half of a ratchet tooth. But the teeth of the conversion cylinder have only half the width of what is needed for reliable engagement, due to the recesses for the cartridge rims in the breech side. To correct this Nedbal opened up the slot towards the center for proper functioning and made a new, wider hand (same as for an original). This is one of the challenges the master needs from time to time to maintain his sharpness I reckon …

December 15, 2009: notches are cut into the cylinder and Nedbal test-fired the Mystery conversion for the first time.

The pistol will be transferred to the Vienna Proof house now for proof testing before the finishing tasks could be completed.

January 30, 2010: the deed is almost done. The Mystery conversion has passed the Viennese proof testing procedure and Nedbal’s contract engraver has applied the proprietary Centaure naval engagement scene with the legend NEW MODEL 44 between the scene’s end.

File written by Adobe Photoshop® 5.0

Nedbal Centaure “Mystery” Conversion #11691 barrel marking CENTENNIAL TRADE MARK       “1960 NEW MODEL ARMY” maintained

She is now ready for the master’s finishing touches: installation of the .429 diameter liner for my .44 Colt inside lubricated bullets, adjustment of the sights to hit POA and finally the rust bluing of the barrel assembly, new cylinder and other formerly cyanide blued parts.

Nedbal Centaure “Mystery” Conversion #11691 - picture courtesy Terushi Jumbo 2012


1st Meeting of the FROCS 2010 & the Tiny Little Details

Due to some business projects I could not put my hands on her before July 16, 2010, unfortunately. But the Centaure “Mystery” conversion was presented to the public on occasion of the 1st Meeting of the FROCS to celebrate 50 years of the Centaure “1960 NEW MODEL ARMY” in Hofheim, Germany, July 17/18, 2010.

Conversion cylinder: 3 digits of serial number, Viennese proof mark, Karl Nedbal NK mark, caliber stamp (left) engraved Centaure naval scene

with NEW MODEL .44 marking between scene ends; diameter of rear segment of cylinder increased like back in the days

Together with the factory engraved Presentation and the FROCS Special the “Mystery” conversion was one of the highlights of the exhibition of Sunday, July 18, 2010. She surely got proper attention of the initiates.

Narrow conversion ring rests like a saddle on frame (left), hole in conversion ring for firing pin, long lip of loading gate (right)

Our visiting FROCS and Centaure aficionados of the German CAS fraction but particularly ruling European champion of the classic cowboy class by the alias Lederstrumpf aka FROCS #30 liked her a lot after firing a couple of rounds at the indoor 25 m pistol range of the club.

Right side view of frame and cylinder (left), proof marks, caliber stamp & Karl Nedbal’s NK under barrel, plugged loading lever slot (right)

Functioning was flawless. Experienced CAS and bulls eye shooters had no issues with the narrow rear sight but some target shooters used to Remington New Model 1863 Armies or Rogers & Spencer Model 1865 had.

Just before the 1st round is fired (left), after 10 round of relaxed shooting (center), tiny rear sight is hard on some shooters (right)

This Centaury “Mystery” is a very special and a one-of-a-kind conversion pistol. None of the US or European conversion artists ever made one to the best of my knowledge! That is until Karl Nedbal got bitten by the vicious Centaure conversion bacillus!

Left side view of Nedbal Centaure „Mystery“ Conversion #11691

Does this re-contoured forward portion of the “Mystery” look like the bow of the yacht to you as well? Now I understand why the US Navy preferred the RM conversion of the Colt 1861 Navy over the 1860 Army, ha!

Mexican connection? Right side view of Nedbal Centaure „Mystery“ Conversion #11691


WDN/June 23, 2013

© 2007 Wolf D. Niederastroth