Archive Logo.jpg

July 09, 2004

Lets look at a cartridge, in detail, eh?

Click the picture for a hi-res view.

In this case, a Canadian-produced .577 cartridge for the Snider rifle. The Snider rifle is a transition rifle, the cartridge is a transition cartridge. The Sniders were the equivalent to the US Springfield Trapdoor or Austrian Werndl rifles, being a conversion of the muzzle-loading Enfield 3 Band musket and it's kin to a breech loading capability. The Snider had a 'flip-open' breechblock that opened to the side, the Trapdoor had a 'flip-up' action that opened upwards, the Werndl rolled to the side.

The cartridge represents the second generation of cartridges, when manufacturers were getting away from pin-fire and rim-fire to center-fire. This cartridge represents the bridge from the early systems to what we have today.

The details are in the Flash Traffic. Click on the thumbnails to open the slides and links - and I recommend you right-click and open them in a new window, so you can go back and forth.

Slide 1. The Base. Here you see the really complex part of the cartridge.

Steel Base Disk. As mentioned elsewhere, case failure during primary extraction was a problem with early metallic cartridges. As the brass alloys had not been fully developed, they couldn’t make a brass with the right qualities of strength and malleability to allow an extractor to act on a brass rim, as we are used to now. So a steel base disk (with all the corrosion issues inherent therein) was used. This held the primer pocket, which consisted of the pocket itself, the anvil, and the primer cup. The cup contains the priming compound, and is held to the base by flaring out the pocket.

Primer Cup. Provides a seal to protect the compound and anvil.

Anvil. Struck by the hammer, the mechanical shock is transmitted to the priming compound, which detonates, flashing through the Flame Hole in the pocket, igniting the charge which explodes, or burns, not detonates. (The difference, you ask? Detonate means the energy is released throughout the ‘energetic compound’ virtually instantaneously. Explodes means the flame front burns through the compound (in this case the black powder grains) with a measureable (still really fast) speed. One has a pressure curve that peaks essentially instantly and drops to zero quickly, the other has a curve that builds fast, peaks, and subsides. You choose your compound based on what you want to accomplish. Note the primer pocket sits in a clay plug, which forces the use of only on flame hole. Modern cartridges have numerous flame holes in the pocket, to speed initiation of the powder. Why’d we do that, you wonder?

Clay Base Reinforce. That plug is there because of the weakness of the layered brass construction. It provides a rigid base for the brass at the base of the cartridge, so that it doesn’t deform during handling, loading, closing the breech, and extraction. Combined with the Brass Base Reinforce, you have enough strength to maintain rigidity of the cartridge, provide a seal when fired, and the strength to survive extraction without ripping off.

Slide 2. The Case.

This cartridge is an example of the second generation of primer-fired metallic cartridges. We still haven’t developed the technology to properly ‘draw’ a fully formed cartridge case from a brass ingot. Problems with the formulation of the alloy, annealing, etc, made it difficult to draw brass into the kind of cartridges we use today with any uniformity and proper strength and malleability. The first cartridges were made of copper, which was found to generally be too soft for the job and suffered corrosion problems. The move to brass started with making a separate, usually steel, base. Then you wrapped brass foil around a mandrel to get the cartridge shape. You mated the two and had a cartridge. A cartridge that suffered from being weak, to being vulnerable to moisture, and subject to ‘case separation’ in primary extraction. That’s where the base of the round would rip off, leaving the rest of the casing inside the chamber, making it impossible to reload. Bad in combat, or when being charged by a pissed-off elephant or other large critter you’ve annoyed. In this shot, you see a paper-wrapped Snider, a wrapped-brass Martini-Henry, and a Swiss 10mm copper rim-fire, with a clip of 8mm Mauser for comparison. As you can guess, this is a comparatively expensive bullet to make. In this slide, from left to right, you see:

Clay Forcing Plug – discussed under “The bullet.”

Felt Wad. Just like in a shotgun round, the felt wad was there to keep the powder compressed, and to assist in making the round water-resistant.

Black Powder Charge. Coarsely-grained black powder. The coarseness is to maximize the surface area of the powder so that it will burn quickly and uniformly, developing it’s max pressure early, and providing a constant rate of expansion as the bullet travels down the bore – with the two goals of it not burning so fast that it causes the barrel to fail at the chamber, nor too slowly that it is still burning outside the barrel, resulting in a loss in velocity for the bullet. You also didn’t want it working too well, as the lead bullet would fail and partially liquefy, cutting range, destroying accuracy, and fouling the barrel, too.

Paper-wrapped brass case. These cartridges were wrapped with a lightly oil-impregnated paper for several reasons. One was lubrication, to aid in extraction, the other was to help seal and waterproof the cartridge. The rumor that the lubricant for british cartridges was pig fat and/or beef tallow (depends on whether the target for the rumor was Muslim or Hindu) was a contributor to the Sepoy Mutiny in India in 1857.

Slide 3. The Bullet

Lead-Antimony bullet. The true “weapon.” Everything else is just a part of the system to get the weapon to it’s intended target. Made of a alloy of lead and antimony to be heavy, easy to work with, deform on impact to provide maximum energy transfer to the target. The antimony acts as a hardener for the lead. To assist in maximum energy transfer there is the “Dum-Dum” cavity.

Dum-Dum Cavity. Dum-dums get their name from the Dum-Dum Arsenal in India, where the British discovered that cutting an “x” in the tip of the bullet made them deform spectacularly on impact, transferring more energy into the target, doing tremendous damage. Not like the lead didn’t do that pretty well already, but, when you are hunting large game or drug-hyped Afghans, anything is a help. There were some obvious problems with that practice, so experiments were carried out and it was determined that casting a cavity in the bullet, with an opening to the nose, gave predictable results, especially regarding the ballistics of the round, maintaining accuracy. Here's a shot of the bullet with the clay plug in the hole leading to the cavity (we've later determined you don't need to do that.

Forcing Cone and Plug. The clay plug was acted on by the expanding gases, pushing up into the cone, which forces the skirt of the bullet into the rifling, ensuring a good seal and a good grip by the rifling. The US discovered in the Civil War that no plug was necessary – the action of the gasses was sufficient to expand the skirt of the bullet.

There ya go. Now you know more about the .577 caliber Snider cartridge than you ever wanted to. Congratulations if you got this far!

Click the pic below for a hi-res view.