The Unique Revolver
The articles written by robocop10mm make a very well detailed treatise concerning reloading and ammunition in general. Just to take them a step further, consider the behavior of cartridges fired in the revolver.
The revolver is unique among all firearms in two ways: (1) The cartridge case head is not rigidly supported when fired. (2) The chamber is not an integral part of the barrel.
Consider the sequence of events when a cartridge is fired in the revolver. The firing pin crushes the priming compound between the primer cup and the anvil, causing a violent explosion. The flash from this squirts through the flash hole in the case head, igniting the powder, and blowing the primer backward out of the case, where it is stopped by the revolver's standing breech. As the powder begins to burn, pressure builds up in the case and forces it backward out of the chamber, re-seating the primer. The bullet begins to move as pressure builds up, until it crosses the gap between the face of the cylinder and breech end of the barrel. As the base of the bullet crosses this gap, high pressure, and very hot, gasses vent outward in a circular pattern. The gasses are blocked by the topstrap of the revolver, and by the bottom of the revolver frame. As the bullet emerges from the muzzle, the remaining gas balloons outward from the muzzle.
While all of this is going on, the revolver also recoils violently, scribing an upward arc in recoil. This arc is created by the off-center forces at work, the resistance of the shooter's hand and arm, and the rearward thrust of recoil. The sharpness of this recoil is determined by the ratio of the weight of the objects set in motion, and the velocity imparted to those objects, those objects being the revolver and the bullet.
From all of this description, some observations can be made. First of all, be sure that the revolver has correct headspace, that is, the distance between the head of a chambered cartridge and the standing breech. There must be some gap here, to allow free cylinder rotation. This is set by the design of the revolver, but a depressed recoil plate, or firing pin bushing, can cause trouble here, and is worthy of observation during casual inspections. If the firing pin bushing is recessed, the primer will not re-seat during firing and cause binding of the cylinder. It's happened to me.
Barrel/cylinder gap is usually now pretty well controlled by the manufacturers and is seldom of concern to the shooter. But it is important to be aware of it as a safety to bystanders. While the gasses vented sideways dissipate rapidly, beware that a bystander, or wayward hand, can get burned by the blast. This of particular concern when shooting small framed revolvers using a two handed hold.
The upward recoil is of concern to shooters who use high performance magnum ammunition. This recoil induces centrifugal force to the cartridges remaining in the cylinder, tending to unseat, or pull, the bullets forward out of the cartridge case. In severe bullet-pill, the bullet may protrude from the face of the cylinder, tying up the cylinder and preventing rotation. Even slight bullet-pill increased the volume of the case, which in turn may prevent powder ignition. The usually used magnum primer will drive the bullet and powder charge up into the barrel, creating a danger if not detected by the shooter. Should a round be fired with such an obstruction, the barrel will be bulged or split, and the cylinder possibly being wrecked also.
While all of the foregoing may be of little concern to the average shooter, the awareness should be there in dealing with used or older revolvers, or with very high mileage revolvers.
And, those who reload their own, especially in the high performance ammunition required in the hunting field of long range silhouette shooting, need to be sure that the proper primer is selected, the brass is sound, and the case provides correct neck tension for the load at hand. Though much of this is purely academic, a good understanding of the basics helps in the accuracy and safety of home made ammunition.
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