Colt Model 1855 Black Powder In-line Repeating Rifle:
The first mass produced black powder percussion cap in-line ignition system rifles were manufactured by Colt for the United States Army in 1855, to which they supplied 4,435 of their multiple shot rotating cylinder rifles.
Modern, Inline Ignition, Muzzleloaded Rifles:
In-line black powder rifle technology was re-introduced in 1985 when Tony Knight created the first modern In-line single-shot muzzle-loading rifle. While the modern inline muzzleloaders may look like modern centerfire rifles they are all still muzzle-loaded.
"Inline Ignition System" refers to the fact that the rifles main powder charge is ignited by an ignition system that is directly behind and in-line with it and the bore of the gun. Inline ignition systems can be either; percussion cap or centerfire primer.
Percussion Cap Ignition; Where a percussion cap is placed over a nipple and a hammer or firing pin must strike the rim of the cap to ignite a powder charge in the barrel.
Centerfire Primer Ignition; Where a modern day centerfire primer is placed into a breech plug and a hammer or firing pin must strike the center of the primer to ignite a powder charge in the barrel.
Modern Inline Muzzle Loading Rifle Action Types:
The types of modern day inline single shot black powder muzzleloader actions can be broken down into four popular types: Bolt Action, Break Action, Drop Action and Plunger.
The bolt-action inline muzzle-loaded rifle appeal to those who like bolt action rifles, most receivers are drilled and tapped for scope mounting. The striker of the bolt has a somewhat faster lock-time than many of the plunger style in-lines, the bolt can be closed over the nipple and provide some protection of the cap from moisture. The major advantage is that you can remove the bolt an breech plug without totally disassembling the rifle in most cases.
The break-action inline muzzle-loaded rifle offers speed in the loading or reloading process, once a charge of powder, wad and bullet goes down and seated in the barrel, with the flick of a switch or lever, the barrel drops down and exposes the breech for priming. Break action muzzleloaders use heavy built metal frames in most cases adding durability to the muzzleloaders action itself. Most now have speed breeches for easy cleaning.
Falling Block Action:
The falling-block-action inline muzzle-loaded rifle (also known as sliding-block or drop-block action), is a rifle action in which a solid metal breechblock slides or rotates vertically into the breech of the rifle and is actuated by a lever. This type action was used on the sharps breech loading black powder rifle in 1848. With the action dropped, the breech is exposed and easily primed after loading the barrel with powder, wad and bullet. This also allows for easy cleaning as well. While not true falling-block actions they are very close, the concept is the same.
The plunger-action inline muzzle-loaded rifle sports a receiver much like that of the bolt action inline muzzleloader, most receivers are drilled and tapped for scope mounting as well. The main difference is that instead of a rotating bolt for cocking the gun it will have a straight pull cocking handle on the side of the receiver. Plunger style guns are usually the lowest dollar inline muzzleloader that anyone can afford. They are however quite accurate, just harder to clean as some disassembly with proper tools will be required.