Restoring a Springfield Model 1866 2nd Allin Conversion Part 1

Share this post

Restoring a Springfield Model 1866 2nd Allin Conversion Part 1

By: Scott C. Radtke

The Springfield Model 1866 rifle holds an interesting place in history. It bridges the gap between muzzle-loading and breech-loading rifles in the US Military and actually served in both capacities. During the Civil War, the muzzle-loader had become obsolete. After that expensive war, Congress was not keen on funding the development of a new breech-loader for use in the west as the US ordnance department had quite a surplus of perfectly good .58 caliber, Model 1863 and Model 1864 Rifled Muskets stockpiled.

Master Armorer Erskine Allin, of the Springfield Armory, designed a system for converting this surplus inventory of Civil War muzzle-loaders to breech-loaders for about ¼ the cost of a new rifle. The first 5,000 of these are known as the Model 1865 1st Allin Conversion. They were modified Model 1863 rifled muskets, chambered for a .58 caliber rim fire cartridge. This conversion was found to be too delicate for military use and extraction problems were frequent. In response, an improved design was developed and the Model 1866, or 2nd Allin Conversion, was born. Using the Model 1864 as the base rifle, the barrel was bored to .64 and an unrifled liner was installed. The lined barrel was then rifled for .50 caliber. Approximate 3″ of the barrel, ahead of the breech plug, was milled off to accept a hinged breechblock. This type of action has come to be known as the trapdoor. The rifle was chambered for the newly adopted 50/70, centerfire cartridge. Approximately 52,000 Model 1866 conversions were produced.

The “new” Model 1866 made a name for itself in the Indian Wars. Two famous battles in 1867 along the Bozeman Trail, the Wagon Box Fight and the Hayfield Fight, attribute their success to the Model 1866. In the Wagon Box Fight a small force of 38 men was able to hold off a far superior force of over a thousand Indians due to the speed at which they were able to reload their rifles.

I became intrigued with this rifle because of its history and decided one would make a nice addition to my collection of I became intrigued with this rifle because of its history and decided one would make a nice addition to my collection of U.S. martial arms as a representative sample spanning the transition from muzzle-loader to breech-loader. An original would probably be outside of my price range, so when I found one that had been sporterized and could be obtained at a reasonable price, I picked it up as a project gun. What better way to test my new AGI gun working skills then to try and return a gun like this to its former glory. Because of the sporterization it had little collector’s value, so I really couldn’t reduce its value by restoring it to its original military configuration. Besides, I always wanted to shoot a military .50 cal! This might be my chance.

Taking inventory of this project gun showed good and bad. The stock was cut off in front of the lower barrel band and very crudely checkered. Unfortunately, the checkering was cut so deep that the stock could not be used in the restoration. The metal parts, with the exception of the butt plate, were in very good shape. They had been cold blued, however, and some parts were also coated with a varnish. The nose cap, upper and middle barrel bands, two band springs, and ramrod were missing. The breech-block hinge mounting screws were in very bad shape as the hinge was soldered to the top of the barrel soldering the screws as well. Someone along the line had tried to remove them without heat. Finally, the muzzle had been cut back about 5/8″. This may have been to clean up muzzle damage at the time the sporterization was done. Obviously, I would not be able to put this back, but the cut was ahead of the original front sight so I felt I could live with it. At least it was not shortened to carbine length.

The first step in restoration was to research this rifle as much as possible. I would need to locate sources for parts, determine the proper finish for the various metal components and explore options for a stock replacement. Richard A. Hosmer’s book, “The .58-and .50-Caliber Rifles & Carbines of the Springfield Armory 1865-1872” proved to be very helpful. It contained detailed information about the military rifles of this time period, giving the proper finishes found on each part. Another book, Claude Fuller’s “The Rifled Musket”, contained Springfield cross reference tables for common parts on Springfield Rifles from 1855 to 1873. This was helpful in correctly identifying missing parts. Additional information was obtained from trapdoor collector forums on the internet. For example, the direction the sanding was done on the barrel and barrel bands by the workers at the armory.

I found parts available from several sources but ended up using two. A partially inlet stock and ramrod was ordered from Dixie Gun Works. Having never fitted a stock of this type before, I opted for one advertised as 90% inlet. I now know what that means. 90% of the parts will not even begin to fit. I should have ordered the 80% inlet stock from a different source and saved about $45. Apparently, the same basic stock is used for the model 1861, 1863, 1864, 1865, and 1866, so the replacement stock I received is actually the lowest common denominator.

When the stock came, everything was oversize and all inletting was undersize. The barrel channel was not deep enough while the wood along the sides of the barrel was too tall. This was actually a good thing but it sure made for a lot of work. Any inletting not common to all models would need to be done. For the 1866 this meant inletting the barrel band spring grooves, nose cap, and all internal cuts to accommodate the extraction system. The balance of the missing small parts was obtained from S&S Firearms of Glendale, New York. I was able to secure all original parts except the ramrod, two screws for the breech block hinge, and the rear sling swivel. Originals were actually available from other sources, but the cost was prohibitive.

Now that all the parts were secured, I disassembled the gun and examined the finish of the metal parts. This rifle left Springfield with an “Armory Bright” finish on the barrel and hardware as it was found that this finish actually saw less corrosion in storage than arsenal blued finishes. There were three exceptions to this finish on the rifle: the color cased hardened lock, the blued rear sight, and the “blackened” breechblock and hinge strap. “Blackened” is a term used to describe the process where the Breech-block was hardened in water with oil floating on the top. The oil would give it a black mottled appearance. The original finish on these three parts was correct and they cleaned up well so I left them as is. The barrel and the rest of the hardware would need to have the cold blue removed.

The breechblock hinge strap and rear sight, which are soldered into place, were removed and work began on restoring the original “finish” to the bright metal parts. After unsuccessful attempts using blue removing chemicals in a discreet area under the breech opening, I decided on 220 to 320 sandpaper followed by 00 steel wool. “Armory Bright” is not a polished finish and this process was giving me good results. I was very careful not to remove any marking, such as the armory eagle head stamp. The barrel was done first using lengthwise strokes. This is reported to be the way it was done at the armory. The barrel bands were sanded perpendicular to that. I cleaned up the screw heads using the methods shown by Bob and Ken on AGI videos. Cleaning up the buttplate required aggressive action with a file first, but when done it now matched the rest.

Next the lock was fit to the stock. The lock area was partially inlet but the lock would not fit. Using soot from a Gun Smoke sight blackening torch, I was able to identify the tight spots and carefully sand and file the wood for a nice tight fit. It was necessary to deepen some of the relief holes for the internal lock screws. This was done with a proper sized end mill. Now the two screw holes for the side plate screws needed to be drilled. The stock comes with a 4”, unshaped area just ahead of the lock that is still a square block. This block is very helpful for clamping the stock and it gives you a reference point for keeping things square. The holes were drilled using the mill as it was critical that they come out in the center of the pre-inlet screw washer recesses on the other side of the stock. If it didn’t, I would have to drill larger holes. When I put the mirror under the work and checked the result I was very pleased.

Subscribe To Our Newsletter

Get updates and learn from the best

More To Explore


The Rest of the Story

S&W M&P 9mm PistolI’m dating myself if I use the phrase “just a silly millimeter longer” but it often occurred to me on this next case. I say case, because it was more of an investigation than a gunsmithing repair. The customer brought me his Smith and Wesson M&P 9 mm. His complaint was that


Sometimes Luck is Better than Being Good

Figure 1: The P85 Ruger’s early entry into the 9mm semi-auto market. The lanyard loop at the base of the grip shows its heritage of being entered in the US army’s 1984 competition to replace the venerable .45 Colt 1911. The other day, a customer brought in a problem that except for a bit of