Brass Quality?

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Llagoud
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Brass Quality?

Post by Llagoud » 17 Feb 2009, 07:33

As I am paying closer attention to cases I noticed a lot of subtle differences from one manufacturer to another.
One difference is what appears to be yellow brass (higher zinc/tin content?) VS. semi-red brass (higher copper content?)
In the world of dihydrogenmonoxide distribution the semi-red is preffered for longevity as zinc is water soluble and eventually washes away creating channels, leaks and damage to the surface attempting to seat on the brass.....
In hand loading is there a preferred brass quality to latch on to? Malleability vs strength?

Grantness
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Re: Brass Quality?

Post by Grantness » 17 Feb 2009, 10:30

:?: but EA says their brass lasts longer than FN's.... so Im happy :D

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Re: Brass Quality?

Post by Llagoud » 17 Feb 2009, 15:17

Here is one example...both new 10mm, the one on the left is Starline the one on the right is Scharch Top Brass

Image

edit: add pic

Image

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Llagoud
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Re: Brass Quality?

Post by Llagoud » 19 Feb 2009, 08:12

OK, it looks like I was chasing my tail with the question.
There does not appear to be any quality differences, and an old dog with some metalurgy background tells me colors can vary slightly due merely to geographic sources and/or negligible contaminations either from raw source copper or recycling.

"Cartridge Brass" by and large is 70/30 copper/zinc with no manufactures that i've researched claiming anything extraordinary about tweaking the mix.

One manufacturer does claim superiority in 'ready to load' quality and wall thickness (reducing case capacity) but no magic is claimed in any blend that I can find.
Effect of zinc content
The problem of selecting the appropriate brass for any particular
service from the range presented is simplified by division into
alpha and alpha-beta brasses.
When up to about 35% zinc is added to copper it dissolves to
form a solid solution of uniform composition. Further increase in
zinc content produces a mixture of the original solid solution
(alpha phase) and a new solid solution of higher zinc content
(beta phase).
Brasses containing between 35% - 45% zinc consist of
mixtures of these two phases and are known as alpha-beta or
duplex brasses, the ratio of alpha to beta phase depending
principally upon the zinc content. The inclusion of certain
third elements - particularly aluminium, silicon or tin - has the
effect of increasing the beta phase content for any particular
zinc content.
The presence of the beta phase in the alpha-beta brasses
gives reduced cold ductility but greatly increased amenability
to hot working by extrusion or stamping and to die casting
without hot cracking, even when lead is present. The alphabeta
alloys are also stronger and, since they contain a higher
proportion of zinc, cheaper than the alpha brasses. However,
they do show higher susceptibility to dezincification
corrosion and are therefore less suitable for service under
conditions where this type of attack is likely to occur.
Alpha brasses
The range of alloys, termed ‘alpha brasses’, or ‘cold
working brasses’, contain a minimum 63% of copper. They
are characterised by their ductility at room temperature,
and can be extensively deformed by rolling, drawing,
bending, spinning, deep drawing, cold heading and thread
rolling. The best known material in this group contains 30%
zinc and is often known as ‘70/30’ or ‘cartridge’ brass,
CuZn30 - due to the ease with which the alloy can be deep
drawn for the manufacture of cartridge cases. The cases
(up to 100mm diameter) start as flat discs blanked from
strip or plate and are successively formed to the final
shape by a series of operations, carried out at room
temperature, which progressively elongate the sidewalls
and reduce their thickness. CuZn30 possesses the
optimum combination of properties of strength, ductility
and minimal directionality which make it capable of being
severely cold drawn. Its ductility allows cold manipulation
and the alloy has better corrosion resistance than the
brasses with a higher zinc content
.
EFFECT OF ZINC CONTENT ON PROPERTIES
Figure 8 shows the effect of variations in zinc content on tensile
strength and elongation of brass wire. It highlights reasons for the
natural popularity of the 70/30 composition since it combines the
properties of good strength and maximum ductility.
Figure 9 shows that both the modulus of elasticity and the
modulus of rigidity decrease progressively, but not too
significantly, with increasing zinc content. These values are used
in the design of spring applications for calculating elastic
deformation
.

Image

Nominal Composition

Cu 70%
Zn 30%
Also known as 70/30 brass, CDA260, CZ106, ISO CuZn30, UNS C26000.
This material also known as cartridge brass since the largest volume of material is used for this purpose in metallic pistol and rifle cartridges. This material has fair to excellent corrosion resistance depending on the contact agents chemistry. It has excellent cold workability and good hot formability. Typical applications include radiator cores and tanks, flashlight shells, lamp fixtures, fasteners, pins, rivets, discs, ammunition components, etc.
Typical Physical Properties

Density 8.53 g/cc
Melting Point 954° C
Typical Mechanical Properties

Ultimate Tensile Strength 43,900 - 130,000 PSI
Yield Strength 11,000 - 65,000 PSI
Elongation @ Break 66%
Modulus of Elasticity 16,000 KSI
Shear Modulus 5800 KSI

To be an effective seal, the case must be somewhat flexible to expand to seal the rear of the barrel, then release to permit extraction. Make the case too hard and gas leaks into the action or, worse, in the shooter's face. Make it too soft and it fails to release from the chamber walls after the pressure drops, effectively jamming the firearm.
Its ductility reaches a maximum with about 30% zinc and its tensile strength with 45%—although this property varies greatly with the mechanical and heat treatment of the alloy. Cartridge brass (70% copper, 30% zinc) is used for cartridge cases, plumbing and lighting fixtures, rivets, screws, and springs

Image


So, until someone tells me different, I am leaving this one alone.

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fatherfoof
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Re: Brass Quality?

Post by fatherfoof » 19 Feb 2009, 09:32

Thank you. This is a rarely discussed area in which I confess I am not well versed. Time to go the metalurgy university types who actually understand this on the molecular level. Appreciate the inspiration.
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Llagoud
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Re: Brass Quality?

Post by Llagoud » 19 Feb 2009, 09:42

fatherfoof wrote: This is a rarely discussed area in which I confess I am not well versed.

There was a surprising lack of discussion anywhere about compositions.
I did run into a lot of info on annealing and I'm still combing it, but as important as the case is, very damn little information is available about differences.


*Thanks MO.

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Re: Brass Quality?

Post by Grantness » 19 Feb 2009, 11:14

Can someone describe a procedure for annealing 5.7x28 brass? This is something I wish I knew more about...especially if I ever run out of 1-2x brass and only have 3x-5x....

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Re: Brass Quality?

Post by Grantness » 19 Feb 2009, 11:28

Thanks MO, that was very informative :thumb: Lets say all I had left was 5x brass, I could anneal them and use them in my FsN if I had to right? Or would the cases just get stuck/jammed all the time?

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gw45acp
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Re: Brass Quality?

Post by gw45acp » 28 Feb 2009, 06:24

I've experimented with annealing 3x and 4x 5.7 brass. Unless you are using it in a TC or custom bolt gun, it's not worth your time and very difficult to do correctly on such a small case. As MO stated, it ruins the lacquer coating. I removed all the coating with steel wool. and the 5 cases I tested in the 5.7 pistol had a 100% FTE rate.

Annealing can only be correctly performed within a very narrow temperature range. Too cool will not change the case metal's internal structure leaving the work embrittled brass unchanged and and too hot will burn the zinc out of the brass, ruining the case.

It is possible to do this correctly, but it is not very practical, especially if you need to re-apply the lacquer coating. Also, since the case is so small, DIY'ers run the risk of annealing the case head area which is a recipe for disaster. Varmint Al has a good explanation of that danger. http://www.varmintal.com/arelo.htm#danger1
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