Why is there brass?

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Why is there brass?

Postby Doug Coulter » Sat Jul 06, 2013 1:18 pm

Brass cases are what really got the gun biz going and practical. Before brass, there were only muzzle loaders - all other attempts to seal a breach were more or less failures. Even today, in all but the largest artillery, cases are used. Why? It's because brass has some very nice and special properties. It (alloy 260) is fairly stretchy and ductile, so on firing, it expands to fill a gun chamber - which is what actually seals it so gun gas, depending on the gun and load, anything from 15.000 psi at the low end (shotgun) to maybe 65,000 psi (HP Magnum) on the other end, doesn't leak out and hit you in the face when shooting. Brass not only holds the other parts, it's the gasket.

For comparison, the peak pressure in a high performance hydraulic system might be 3500 psi...gun pressures are no joke. A hydraulic leak at 1500 psi will cut your arm off. Fifty times that?

After firing, the brass springs back a little, so you can easily extract the case. Again, this is due to the right alloy - a perfect spring would come back to the original size. And if you're a tweaker, this case is now the most precise fit into that particular gun's chamber it's possible to produce, leading to high accuracy if you only re-size the neck to grip the next bullet you reload into it - but you can only shoot it in the same gun after that.

Some cheap ammo uses steel cases, and these are not reloadable for a good reason. Steel doesn't stretch as well (most of them use paint to get the seal, and prevent seizing steel-steel, not a problem with brass) and steel work hardens and gets too brittle after just one go. The makers of steel cases deliberately use a Berdan primer that's hard to punch out and replace, for just this reason (they are also cheaper), and most also use cheap, dirty-burning powder that fouls guns quickly - so I just plain avoid those (Wolf comes to mind, so bad they've changed their name so they can stay on the market at all).

Note, as RIchard Lee has, that brass alone is no where near strong enough to contain the pressures involved in modern shooting. That's why the rest of the gun has to be wrapped around it and strong enough to contain things. The brass will, in just about all cases, expand to fit whatever space there is when firing the gun, so the gun needs to be strong and rigid, and things have to more or less match in size, or the brass can break and release gas. Most guns have some extra holes in the mechanism to vent this gas - not always enough to prevent a minor injury, however, and bits of brass coming out of those holes are pretty dangerous. It's a situation to prevent...

Brass also performs the function of holding the primer in the center, where the firing pin will strike it, and provides the "anvil leg seat" for a boxer primer to be crushed against. Further, it holds the bullet with a known release tension, and holds it in alignment with the gun bore accurately, that is, if you do your part in preparation, which is crucial to accuracy - "Only accurate guns are interesting" (Jeff Cooper).

There are a lot of words about "headspace" out there. What we mean by that is the fit and length of the brass relative to the chamber of the firearm. There are several systems for headspacing (all assuming you've got a correctly made gun/chamber, which we'll assume for the moment). One of the oldest is simply to put a rim on the case - most revolver ammo for example. This locates the brass and the rest by having this rim come up to a stop on the revolver cylinder. Only one pretty famous rifle uses this - the Mosin Nagant from Russia, since with that rim sticking out, it makes the rounds hard to feed from a clip or magazine. There are other issues that make other schemes better for rifles, now in wide use.

In belted magnums, there is a belt near the case base that is larger in diameter which is what controls how far into the gun the ammo goes. It looks "masculine", I suppose. It really isn't significantly stronger, and makes sizing to the really correct length more complex, since the shoulder of the case, as long as it's shorter than the rest of the chamber, will go in, no matter what - but if you size it too short, the brass gets an extra stretching that makes it die young, so only a few die-hards still use this case style (guns last a long time), and there's an entire art of sizing it just so - so that we still wind up using the modern method - locating off the shoulder, the angled neck-down part. I don't shoot belted mangums for that reason - it's just too finicky to get right and get decent case life - and they aren't cheap.

This is much easier to get right - just space off the shoulder and you're good. If the gun is poorly made (too much headspace), or you set up your sizing dies wrong, you could have a situation where the case is then so far into the chamber the firing pin won't reach it to give the primer a good solid hit. Well, the solution there is obvious - fix the gun - or set up your sizing die correctly, which these days is pretty easy - for nearly all cases, you simply set the die up so the shell holder touches the base of the die when the press ram is fully up, and you're done. Yes, you can fine tune this if you want a little longer brass for less "head-space" or in the case of just keeping fireformed brass mostly still fireformed at full chamber diameter, you can set up a die to just kiss the shoulder and not reduce the diameter (much), which also preserves the live of the brass - the more bending the sooner it will fail.

Pistol cases (for semi autos) almost universally headspace off the top of the case - right behind the bullet. Pressures are lower, so blowback mechanisms are often used, rather than a more solid bolt lockup, or the scheme in a 1911 pistol, which has an intrinsic lock of slide to barrel and slows down the blowback and extraction. Headspace (this is heresy to some) is not quite as important here, at least not to brass life, but obviously, too short and the firing pin won't reach, too long and the gun won't go into battery and fire - so lengths always matter, whatever the scheme for locating the cartridge is. And it really barely matters at all in a revolver - if the cylinder will close, you're good to go. You can, for example, regularly shoot .38 special in a revolver made for .357 magun (they are the same diameter in actuality) - even though the .38 is about 1/10th inch shorter. It does cause some extra cleaning issues in the cylinder, since more of it gets fouled by powder, before you shoot the full length .357 mags again, but that's not a really big deal. You keep your guns clean, right?

Brass can also be crimped around a groove cut into a bullet (or even if there isn't one, but that's a bad idea in general, as things don't bend straight). This is mostly used in semi-auto arms (where a near mis-feed might cram the projectile back into the case too far for safety), or arms with such severe recoil that the bullets might pull out of the brass before firing the next one. Crimping is a touchy subject deserving its own thread. To keep it short here - if you're going to do it for pistol ammo, you use a taper crimp, and you get it precisely correct or it's worse than nothing, which in turn, with most tools, means the brass has to be precisely the correct length, or you get either no crimp - or too much, which then allows the brass to skip past the locating step in the chamber - and either maybe not fire, or not be willing to extract later, both bad. For rifle ammo, crimping almost always reduces accuracy while sometimes increasing reliability, but again, with most tools - things have to be just so, or you make bent ammo that won't shoot straight. For this, I like the Lee factory crimp dies, which are a lot less touchy about this - they have a patent on it that no one else licenses, so that's the only source for the "right tool for the job" at present. Bullets that can be crimped well and safely have a groove for this, called a cannelure. They are the only type that should be crimped. Needless to say, this takes away some flexibility in overall length of the round as you have to stay within that groove with your crimp.

The military, for whom auto loaders are de rigeur, and reliability essential in battle, loves to crimp things, both bullets and primers, into rounds, to make them work even though mis-handed by idiots. Duh, did I say that? I have great respect for the guys in the military I've met who've "seen the elephant" - and they aren't idiots at all - but sometimes they are under a lotta stress in a situation and dinging the equipment isn't their first concern, staying alive is. Since we are not in that situation, we can skip most of this junk entirely. Other uses for crimping, for instance on "elephant guns" (or .44 magnum class "handguns") - sure, you're only using those at short range where your hold is the accuracy limit (due to adrenalin, danger, and the need for speed), not the gun in most all cases. I put handgun in quotes above. Just because you can put a one-hand handle on it doesn't make it a handgun, in my rarely humble opinion. I've seen too many injuries when small people with low arm strength shoot these guys. It's not fun getting hit in the forehead with too big a handgun coming back fast in recoil - it does leave a mark.

So brass is pretty amazing stuff - it also has the property of being a bit softer than steel, while refusing to stick to it easily, which allows for case extraction after a shot. That's why we reloaders spend so much time on this. It doesn't escape notice that it's also the only reusable part of a loaded round...for saving money. However, most reloaders use the money they save to simply shoot more and get better at both shooting and loading, which I feel is a good thing. Doesn't matter how good your gear is if you're out of practice - and shooting is a perishable skill. And what use is the second amendment if no one has any ammo? The mere existence of so many handloaders ensures than no ammo ban will ever really work...So I suppose you could consider it a patriotic act to be one, that is, if you think believing in the Constitution - or just the Bill of Rights, is patriotic, unlike apparently, our current government.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Doug Coulter
 
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