The Henry Big Boy Mare's Leg Side Gate is a lever-action pistol chambered in .45 Colt. It has a 12.9-inch octagonal blued barrel, polished hardened brass receiver, American walnut stock, and an overall length of 25 inches. Capacity is 5+1 rounds, and the gun weighs 5.79 lbs. 
 

Key Specifications 

• UPC: 619835060754 
• Caliber: .45 Colt (LC) 
• Action: Lever Action 
• Capacity: 5+1 rounds 
• Barrel Length: 12.9 inches 
• Overall Length: 25 inches 
• Weight: 5.79 lbs. 
• Sights: Brass Bead Front / Fully Adjustable Semi-Buckhorn Rear with Diamond Insert 
• Barrel Type: Octagon Profile 
• Finish: Polished Hardened Brass Receiver / Blued Barrel 
• Stock Material: American Walnut 
   

Detailed Features 

• Side Gate Loading: The side gate on the receiver allows loading individual rounds directly into the magazine tube from the side, similar to a traditional cowboy-action loading gate. This is faster and more intuitive than muzzle-end tube loading. 
   
• Octagonal Barrel Profile: Traditional look consistent with the Big Boy line. The 12.9-inch barrel is legally classified as a pistol in most jurisdictions (under 16 inches), which affects how it must be purchased and transferred. 
   
• Transfer Bar Safety: Prevents the firing pin from contacting the primer unless the trigger is fully depressed, allowing the hammer to rest on a loaded chamber safely. 
   
• Adjustable Semi-Buckhorn Rear Sight: Adjusts for windage and elevation; the diamond insert aids sight alignment in varied lighting. 
   
  The .45 Colt cartridge in a 12.9-inch barrel produces less velocity than a rifle-length barrel, which limits effective range. The combination is well-suited to 50 yards and under. Note that the pistol classification means a transfer through an FFL is required.

The Mare's Leg in .45 Colt appeals to buyers who want something visually distinctive with functional lever-action mechanics. The brass-and-walnut aesthetics get consistent positive feedback, and most owners describe the build quality as solid for a production Henry.

The lever action cycles smoothly, and .45 Colt at pistol-length velocities is a capable close-range cartridge for small game, pest control, and recreation. Accuracy at 25-50 yards is generally reported as satisfying.

Ergonomics generate the most varied feedback. The short overall length and pistol configuration feel natural to some shooters but awkward to others, particularly for extended sessions. The weight at 5.79 lbs. is notable for a pistol-length gun.

Practicality versus novelty is a recurring debate. Opinions differ on whether the Mare's Leg is a functional tool or primarily a conversation piece. Most buyers are honest that they were drawn partly by the distinctive look -- a connection to Western and TV-cowboy culture -- while still appreciating that it functions reliably.

The pistol classification (NFA rules do not apply, but an FFL transfer is still required) occasionally surprises first-time buyers unfamiliar with the 16-inch barrel threshold for rifles.