What causes stacking?

Wednesday, June 06, 2007 Filed in: Revolvers, Gunsmithing
Stacking is defined as an increase in trigger pull weight toward the end of the trigger's rearward travel. Some people like it, some don't, and different guns have varying amounts of it. What causes it?

Some people come up with odd explanations. I recently got an email asking about stacking; the writer had read "on the internet" that stacking was caused by the type of spring - coil or leaf - used in the action. It's a simplistic answer, and it's not terribly accurate.

An "L" frame S&W uses a leaf spring, and has little to no stacking; a Colt uses a leaf spring, and has lots of stack. A Dan Wesson uses a coil spring and it's trigger stacks horribly, where a Ruger GP-100 uses a coil spring and stacks very little.

The cause of stacking isn't the spring itself; the biggest determinant is the geometry of the double-action mechanism. In general, guns using a design where the hammer strut does double duty as the double action sear (Colt and Dan Wesson) will display lots of stacking, while those that use a separate strut and sear arrangement (S&W, Ruger) will display less.

(Some nomenclature: a sear is any pair of surfaces from which the hammer is released; a strut is the pivoting piece on the hammer, which the trigger pushes on in order to start the hammer moving backward. In some guns, the trigger pushes on the strut, and at some point the sears come into contact and the strut leaves contact with the trigger; after some additional hammer movement, the sears slip out of engagement and allow the hammer to fall. The other design is where the strut actually pushes the hammer all the way back, at which point it slips off of the trigger and releases the hammer.)

This isn't a guarantee, though, because there are still a number of angles between surfaces and pivots that can introduce stacking into the mechanism. It is possible to design either system to have the characteristics of the other, though in practice it doesn't happen all that often.

That's how it all stacks up! (Sorry, couldn't resist the pun.)

-=[ Grant ]=-
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