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January 19, 2023

Trigger Mechanism ABCs

By Seth Isaacson

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The trigger mechanism on a firearm is what releases the lock or action to fire the gun. Trigger mechanism designs pre-date firearms by centuries and were developed for crossbows and other early projectile weapons, and then some of these designs were adapted for early firearms. Over the centuries, the trigger mechanisms was designed and redesigned for firearms. The first triggers were primitive, but as guns became more advanced, so did the mechanics to fire them.

On some of the early matchlocks, for example, the trigger was directly attached to the match holder and was pinned to the side of the stock and just swiveled back and forth to bring the match down on the powder, but it wasn’t long before gun makers started to develop a better trigger mechanism. Matchlock firearms were the first to see advancements in trigger mechanism designs and lock mechanisms, culminating with the snap matchlock and a trigger mechanism that pivots rearward and contacts the arm on the sear of the lock to release the tumbler attached to the serpentine/match holder causing it to rotate towards the flash pan and fire the gun. This basic trigger mechanism became the standard trigger design for many firearms going forward.

Plain Trigger Mechanism

With a plain — or standard — trigger mechanism, the shooter simply pulls back on the trigger to engage the sear and release the action. On some early antique firearms, the trigger is only pinned in place in the stock. Others have the trigger installed on a trigger plate. It pivots so that the trigger applies pressure on the sear releasing the lock or action. Plain triggers are commonly found on pistols, muskets, fowling pieces, shotguns, rifle muskets, and standard grade sporting rifles. A plain trigger can be set up to allow for a very light and smooth trigger pull, but they will generally require more pressure than set triggers.

A plain trigger mechanism like the one on this percussion American jaeger rifle, available as Lot 120 in Rock Island Auction Company's Feb. 14-17 Sporting & Collector Auction, is the most common trigger mechanism on antique firearms.

Plain Double Trigger Mechanism

The plain double trigger mechanism generally consists of a trigger plate with two triggers installed, generally one on the right fitted ahead of one to the left, so that the right trigger fires the lock for the right barrel and the left trigger fires the lock for the left barrel of a double barrel shotgun, rifle, or pistol. Similar arrangements may also be used on over/under guns and combination guns. Some three-barrel drillings (with two shotgun barrels and one small caliber rifle barrel) will have double triggers and a selector switch  for the right trigger to fire either the shotgun barrel or the rifle barrel. On many drillings, the left trigger is designed as a plain trigger while the right trigger can be either a plain trigger for the right barrel or alternatively as a single set trigger for the rifle barrel.

The trigger mechanism on this engraved C. Willmer, Grantham double barrel shotgun is a plain double trigger. This shotgun, Lot 2275, is available in Rock Island Auction Company's Feb. 14-17 Sporting & Collector Auction.

Single Set Trigger Mechanism

Using a single set trigger mechanism, pressing the trigger forward sets the trigger under spring tension so that a lighter pull releases and causes it to hit the sear, releasing the lock/action. You can also just fire the gun by pulling the trigger like a plain trigger mechanism. Because they take up less space than double set triggers, single set triggers are common on English flintlock and percussion dueling pistols, and may be found on some rimfire and centerfire target rifles, pistols, and other special order sporting rifles such as Winchester’s classic lever actions.

This engraved nickel plated Winchester Model 1873 has a number of special features highlighted in an included factory letter that lists an octagon barrel, single set trigger, nickel plating and engraving. This lever action rifle is Lot 24 in Rock Island Auction Company's Feb. 14-17 Sporting & Collector Auction.

Single Phase Double Set Trigger Mechanism

Single phase double set trigger mechanism designs have been around for a long time. They were first used on crossbows and can be found on 16th and 17th century Germanic wheellock rifles and many later muzzleloading rifles. With a single phase double set trigger mechanism, pulling the rear trigger sets the forward firing trigger and places it under spring pressure for a very light trigger pull. Pulling the front trigger without it set will not fire the gun. This makes it a fairly secure system. They are generally adjustable to raise and lower the amount of pressure the shooter needs to apply to the trigger. These triggers are very common on American long rifles (aka Kentucky rifles) and Germanic jaeger rifles.

This engraved relief carved and Goss signed contemporary flintlock American long rifle has a single phase double set trigger mechanism and is available as Lot 4092 in Rock Island Auction Company's Feb. 14-17 Sporting & Collector Auction.

Double Phase Double Set Trigger Mechanism

With a double phase double set trigger mechanism, pulling the rear trigger sets the forward firing trigger. However, unlike the single phase double set triggers, you can also fire the gun using the front trigger without setting it first. This makes it a more versatile trigger mechanism giving the shooter the option for a lighter “hair trigger” setting or a normal trigger pull.

This type of trigger mechanism is also common on American long rifles and German jaeger rifles, as well as 19th century target rifles, special order Winchesters, and other sporting rifles designed for precision shooting.

It isn’t uncommon to find antique rifles, particularly plainer percussion rifles, with single or double phase set triggers that will not properly lock up unless the trigger is set before cocking. If you find a rifle set up in the former manner, you can sometimes adjust the tension screw to allow the rifle to cock without setting the trigger. However, other adjustments to the trigger group or lock may be necessary.

This Sharps Model 1874 single shot sporting rifle has double set triggers. It is available as Lot 73 in RIAC's Feb. 14-17 Sporting & Collector Auction.

Close Coupled Double Set Trigger Mechanism

This trigger mechanism design was used on some Winchester rifles. This mechanism has two triggers, but instead of pulling the back one to set the trigger group, you push it forward like a single set trigger. When you pull the front trigger, it releases with a lighter pull than just pulling the trigger unset.

This Winchester Model 1894 takedown rifle offers a number of special features including matted and extra light round barrel double set trigger, half magazine and fancy checkered stock." It was sold in RIAC's December 2022 Premier Auction.

Other Trigger Mechanisms

These are the main trigger mechanisms used on antique firearms and are generally what you’ll find on muzzleloading rifles, dueling pistols, Sharps rifles, and other classic 19th century cartridge rifles. Still, there are other very rare varieties. In the 20th and 21st centuries, firearm designers have come up with several other trigger mechanism designs such as binary triggers, release triggers, and more. If you want to read more about these modern trigger mechanisms, let us know!

In addition to the trigger mechanisms we’ve discussed, there are a host of other less common trigger mechanisms that have been used on firearms throughout the years. For example, this factory game scene engraved Emil R. Martin Drilling with Zeiss scope has three triggers, one for each barrel. It will be available in Rock Island Auction's May Premier Auction.

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