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January 20, 2023
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Current Miroku-manufactured Winchester Model 1873 rifles in .44-40 Winchester (.44 WCF) are held to modern SAAMI barrel specifications rather than the loose, inconsistent tolerances typical of late 19th-century originals:
Bore Diameter (top of the lands): 0.422″ to 0.4225″ (nominal SAAMI spec is 0.422″, with production targets typically at 0.4224″–0.4225″)
Groove Diameter (bottom of the grooves): 0.4285″ to 0.429″ (SAAMI specification minimum is 0.4285″, with a +0.002″ tolerance window up to 0.4305″)
Rifling Twist Rate: 1 in 36 inches (standard for modern .44-40 lever guns)
Handloading & Bullet Fit Implications
Standard .427″ jacketed bullets: Traditional .44-40 factory jacketed bullets measuring .427″ will shoot safely, but because the groove diameter sits around .4285″–.429″, accuracy with undersized .427″ hard-cast bullets often suffers due to gas blow-by and bore leading.
Lead / Cast bullets: Sizing cast bullets to .429″ (or soft-cast/20:1 alloy up to .430″) generally produces optimal accuracy and a proper gas seal.
Chamber neck clearance: Because the .44-40 case neck is thin (.007″–.008″), loading a .429″ or .430″ bullet into modern brass (such as Starline) typically yields an outside neck diameter well within the SAAMI maximum chamber neck limit of .443″, allowing rounds to chamber smoothly without neck-turning.
- Bill
WACA # 65205; life member, NRA; member, TGCA; member, TSRA; amateur preservationist
"I have seen wicked men and fools, a great many of both, and I believe they both get paid in the end, but the fools first." -- David Balfour, narrator and protagonist of the novel, Kidnapped, by Robert Louis Stevenson.
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