For those who like to "peek behind the curtain" I'll post a few photos of the inner workings. Here is a rather poor photo of the locks of my .303 rifle:

doubleriflejack has given a good explanation of how the Beesley system works. Even so, it's a bit hard to comprehend (at least for me, that is). These photos illustrate that when the lock is at rest the tumbler is in the cocked position, without spring tension.

One of the more interesting aspects of the system is to understand how the mainspring is tensioned. This is key to understanding how the lock works.

Here is a little brighter photo of the left lock of that rifle:

Notice the cam situated above the mainspring just to the rear, and above, the bar. The screw that secures the locks to the action extends through the central pivot of this cam. And to the rear of this cam is the buttress against which the tumbler falls if the rifle is dry fired. This cam impinges against a roller attached to the mainspring. You can see the roller behind the mainspring, secured by a small screw.

Now have a look at the water table:

You can see at the front of each bar there is a cam mounted on an axis in line with the hinge pin. There is a rod extending rearward through each action bar with one end impinging on the curvature of this cam.

As the barrels close these cams are rotated downward within the hinge, toward the water table. The curvature of these cams pushes the rods rearward. The other end of each rod impinges on the mainspring cam, previously mentioned. The mainspring cam rotates rearward with its curvature working against the roller attached to the mainspring, and thus depresses the top member of the mainspring. This supplies tension to the tumbler, working through the bottom member of the mainspring, which is linked to the tumbler by the stirrup.

When the trigger trips the sear out of bent, the tumbler rotates forward under spring tension to strike the firing pin. As this happens, the bottom member of the mainspring flexes downward while the top member remains stationary. However, not all of the spring tension is released by this movement.

Having fired the gun the shooter now opens it. The residual spring tension of the mainspring works in reverse against the mainspring cam, which in turn works against the cocking rod, which works against the knuckle cam, supplying force to open the barrels. As this happens, the top member of the mainspring flexes upward. In doing so, the rear portion of the mainspring, which has such an interesting shape, cams against the roller on the foot of the tumbler, thus rotating the tumbler back into bent and pulling the bottom member of the mainspring back into the position of the photograph. That completes the cycle that began by closing the action.

One very favorable by-product of this design is the strength afforded the action bars. On a gun with H&H type sidelocks or a normal boxlock, the tumblers are cocked by Anson & Deeley levers situated inside the action bars. A lot of metal must be milled out of the action bars to accommodate these levers. Much less metal is removed in a Beesley actioned gun: only holes drilled though sufficient to accommodate the cocking rods seen above. Look at the next photo and notice how solid the action bars remain.

Frederick Beesley was a genius. How he could invent something so elegant and utterly functional is amazing to me. I think Jack hit the nail on the head when he said it is the pinnacle of sidelock design.

Curl