Springfield Model 1866
The Springfield Model 1866 was a single-shot breech-loading rifle produced at the Springfield Armory from 1866 to approximately 1873, converting surplus Civil War-era Model 1861 muzzle-loading rifle-muskets using Master Armorer Erskine S. Allin's trapdoor mechanism to chamber the new .50-70 metallic centerfire cartridge.[1][2] This "Second Allin" conversion, formally adopted by the U.S. Army following evaluations by ordnance boards, addressed reliability issues from the earlier 1865 rimfire prototype by incorporating a more robust hinged breechblock and extractor for improved handling of the centerfire round.[3][4] Approximately 25,000 such rifles were manufactured, serving as a transitional arm that enabled rapid modernization of the post-war arsenal at low cost without full replacement of existing stocks.[1] The Model 1866 saw its first combat in 1867 during the Wagon Box Fight near Fort Phil Kearny, where its breech-loading design demonstrated advantages over traditional muskets in frontier conflicts against Native American forces, though it was later superseded by the refined Model 1873 in .45-70 caliber.[4][2]Development
Origins of the Allin Conversion
Following the American Civil War, the U.S. Ordnance Department faced the challenge of modernizing its vast stockpile of approximately one million .58-caliber percussion muzzle-loading rifle-muskets, primarily Springfield Model 1861s, without the expense of manufacturing entirely new arms.[1] In mid-1865, Erskine S. Allin, Master Armorer and superintendent at the federal Springfield Armory, was directed to devise a practical breech-loading conversion system that preserved the existing barrels and stocks while enabling the use of metallic cartridges.[4] Allin's solution involved milling away the upper rear portion of the barrel to create a chamber and affixing a hinged, spring-loaded breechblock—known as the "trapdoor"—that swung upward to load cartridges, a design emphasizing simplicity, durability, and minimal alteration to proven components.[1] Allin formalized his trapdoor mechanism through U.S. Patent No. 49,959, granted on September 19, 1865, which detailed the breechblock's pivot, latch, and extractor integration for reliable operation with rimfire cartridges.[1] This patent built on earlier experimental breech systems tested by the Ordnance Department but prioritized cost-efficiency, as full replacement rifles like the Sharps or Henry would have strained federal budgets amid postwar reconstruction. Initial prototypes underwent rigorous trials at Springfield Armory and Frankford Arsenal in late 1865, demonstrating superior gas sealing and reduced fouling compared to competing conversions like the Snider or Remington Rolling Block, though early models retained the .58 rimfire cartridge for compatibility.[1] The origins of the Allin Conversion thus reflected pragmatic engineering amid fiscal constraints, with Allin receiving $1 for assigning his patent rights to the government, underscoring the design's alignment with military priorities over commercial innovation.[5] Conversions commenced in December 1865, yielding about 5,000 Model 1865 rifles as proof-of-concept pieces, which informed refinements in the subsequent Model 1866 production.[6] This approach not only extended the service life of wartime arms but established the trapdoor as a foundational U.S. infantry rifle mechanism through the 1870s.[7]Improvements from the Model 1865 Prototype
The Springfield Model 1866 incorporated several key enhancements to rectify the operational shortcomings of the Model 1865 prototype, which suffered from unreliable extraction and a fragile breech action during limited testing. Chief among these was a redesigned breechblock mechanism featuring a simplified extractor and a reinforced hinge, which improved reliability and reduced the complexity that had plagued the earlier version's extraction process.[2][1][8] Another critical upgrade involved the barrel configuration, where a .50-caliber liner sleeve was inserted into the original .58-caliber muzzleloading barrel, enabling compatibility with the more robust .50-70 Government centerfire cartridge rather than the problematic .58-caliber rimfire round used in the 1865 prototype. This shift addressed frequent jamming and inconsistent ignition issues inherent in the rimfire ammunition, while the sleeved barrel maintained structural integrity without requiring full replacement of existing stocks.[1][8] These modifications collectively resulted in a more streamlined and durable trapdoor action, facilitating smoother loading and ejection under field conditions, though the overall conversion process still relied on milling out the rear barrel section to accommodate the hinged breech. Approximately 25,000 Model 1863 rifle-muskets were adapted to this configuration, marking the transition from experimental prototype to standardized production arm.[9][1]Design and Features
Breech Mechanism and Cartridge
The Springfield Model 1866 employed a trapdoor breech-loading mechanism designed by Erskine S. Allin, master armorer at Springfield Armory, which converted existing .58-caliber muzzle-loading rifle-muskets by removing the upper rear portion of the barrel and replacing it with a hinged breechblock.[4] This breechblock, secured atop the barrel, operated via a thumb-actuated cam latch that pivoted it upward and forward to expose the chamber for cartridge insertion and extraction.[1] The design incorporated an extractor to remove spent cases, facilitating reliable cycling.[1] Relative to the preceding Model 1865 prototype, the 1866 iteration simplified the breechblock construction, reducing the number of machining steps from approximately 56 and eliminating the complex, prone-to-rattling components of the earlier toothed extractor-ejector system.[1] The barrel was reamed smooth internally and fitted with a .50-caliber liner of wrought iron or steel, which was then rifled to accept the new ammunition.[4] These modifications enhanced mechanical reliability and transitioned the arm from rimfire to centerfire ignition, supporting improved ballistic performance.[1] The rifle chambered the .50-70 Government cartridge, a rimmed centerfire black powder round featuring a .50-caliber (0.512-inch diameter) 450-grain lead bullet seated over 70 grains of powder for standard rifle loads.[10] This ammunition delivered a muzzle velocity of about 1,260 feet per second and muzzle energy of 1,488 foot-pounds, offering greater effective range and accuracy than the .58 rimfire cartridges used in prototypes.[10] The cartridge case measured 1.75 inches in length, with an overall loaded length of roughly 2.25 inches, and its rimmed base ensured positive headspace and extraction within the trapdoor system.[10]Barrel and Stock Configuration
The barrel of the Springfield Model 1866 consisted of modified .58-caliber barrels from existing Springfield rifled muskets, relined with a brazed iron or steel liner to achieve a .50-caliber bore compatible with the .50-70 Government centerfire cartridge. The relining process entailed reaming the original barrel to roughly .64 caliber, inserting the liner, and then rifling it with three lands and grooves featuring a right-hand twist of one turn in 42 inches. Standard rifle barrels measured 36.6 inches in bore length, with the rear portion milled to accept the trapdoor breechblock.[11][1] The stock was fashioned from walnut, utilizing Civil War-era musket stocks that were internally altered to fit the new breech mechanism while preserving the external full-length configuration. It employed three Model 1863-style barrel bands spaced 11 1/16 inches apart to secure the barrel, maintaining a traditional infantry rifle profile. The assembled rifle achieved an overall length of 55 15/16 inches, complemented by a 38 5/8-inch threaded cleaning rod of varying diameters.[11] Short rifle variants featured shortened barrels and stocks with two bands, while cadet rifles used thinner stocks on abbreviated barrels, rendering them more susceptible to damage. These configurations prioritized conversion efficiency over new manufacturing, reflecting post-Civil War resource constraints at Springfield Armory.[11]Accessories and Bayonet Compatibility
The Springfield Model 1866 trapdoor rifle, as a conversion of surplus Model 1861 and 1863 percussion muskets, retained the original bayonet lug at the muzzle, ensuring full compatibility with the U.S. Model 1855 socket bayonet that had equipped those earlier rifles.[9] This bayonet, characterized by its 18-inch triangular blade and angular socket calibrated for .58-caliber bores, fitted securely over the Model 1866's barrel without alteration, as the conversion process preserved the muzzle dimensions despite the shift to .50-70 centerfire cartridges.[12] Approximately 25,574 Model 1866 rifles were produced between 1866 and 1867, all issued with this standard bayonet pattern, which remained in service through subsequent trapdoor models until the adoption of the Model 1903.[9] No unique accessories were developed exclusively for the Model 1866; instead, it utilized standard U.S. Army infantry equipment adapted from percussion-era designs. Leather slings, secured by swivels on the lower barrel band and the stock's forend, were standard for transport and field carry, mirroring those on Model 1863 muskets.[13] The rifle's full-length stock and 40-inch barrel also accommodated the original ramrods from converted muskets, primarily for cleaning the bore rather than loading, given the breech mechanism's efficiency with metallic cartridges.[14] Bayonet scabbards, typically of leather with metal fittings, were issued separately but conformed to pre-existing patterns compatible with the Model 1855 blade.[13]Production
Conversion Process at Springfield Armory
The Springfield Model 1866, designated as the Second Allin Conversion, transformed surplus .58-caliber Model 1863 rifle-muskets into breech-loading rifles chambered for the .50-70 Government metallic cartridge, with conversions conducted at Springfield Armory from 1867 to 1869 under the direction of Master Armorer Erskine S. Allin.[1] This process prioritized economical reuse of existing components, retaining the original lockplates (typically dated 1863–1865), ramrods, leather slings, and bayonet lugs compatible with the M1855 pattern, while focusing modifications on the barrel and breech to enable rapid reloading from a prone position at 8–10 rounds per minute.[1][15] The barrel alteration began by milling or cutting out the rear portion of the .58-caliber tube to expose the breech area, followed by reaming the bore to approximately .64 caliber to accept an iron liner sleeve. This sleeve was inserted, brazed securely in place, and then rifled with three grooves to achieve the final .50-caliber dimensions suitable for the centerfire cartridge, enhancing accuracy over the original muzzleloader while minimizing material waste.[1][7] A simplified hinged trapdoor breechblock, featuring a cam-locking mechanism, was then fastened to the modified breech via hinges and a leaf spring, differing from the more complex rack-and-pinion design of the 1865 prototype by offering greater reliability and ease of operation for extracting spent cases.[1][7] Stock adjustments were minimal, primarily involving inlet modifications to accommodate the new breechblock without altering the overall length or profile significantly, ensuring compatibility with existing infantry drill practices. Approximately 52,000 units underwent this conversion, though some accounts cite 25,000–50,000 based on issuance records, with the Armory employing standard machining tools like mills, reamers, and rifling benches for precision work.[1][7][15]Production Quantities and Timeline
The Springfield Model 1866 trapdoor rifles were produced through conversions of surplus Civil War-era Model 1861 percussion muskets at the Springfield Armory, with the primary timeline spanning 1867 to 1868.[16] Unlike later models, Model 1866 rifles were not assigned serial numbers during manufacture.[16]| Year | Rifles Produced | Cadet Rifles Produced |
|---|---|---|
| 1867 | 49,257 | 320 |
| 1868 | 1,796 | 104 |
| Total | 51,053 | 424 |