Metallurgists tell us that drawn brass is much stronger and more durable because the grain structure is actually rearranged during the process.
From RCC's web site:
The draw process has been used for cartridge manufacturing since the 19th century and manufacturers have been able to develop this process to produce high volumes of brass cases. Draw cartridge manufactures have tested many different types of materials over the years and the best material for this process is a brass alloy with a mixture of 70% copper and 30% zinc.
When brass is annealed at 250° C there is no visible change to the bonding of the grain structure, tensile strength, and elasticity. At 300° C, there is a microscopic change to the grain structure and at 350° the work hardness becomes softer and a fine grain structure can be seen. As temperatures increase the brass becomes fully annealed at 750° C and large crystals can be seen. Temperatures above this point will cause damage to the brass and at 800°C, the brass is burned and should be scrapped.
When brass is cold-worked it hardens and done by bending, drawing, compressing, and so forth. This increases the tensile strength and decreases its elasticity. To accommodate today’s high-pressure cartridges brass must both have a high tensile strength to withstand pressure spikes and elasticity to seal the chamber from any gas blowback.
The draw process begins using a brass cup that is annealed and cleaned to remove any scale build-up that might have occurred. During the first draw, the cup is pushed through a die with a punch and extruded to lengthen the cup. It has become work-hardened and has to be annealed and washed for the second draw. Typically a cartridge will go through 4 draws before it is ready to go to the next stage. The case head will be turned, primer pockets, flash holes, headstamps, and necks are done to complete the manufacturing process. When the neck is formed the cartridge is annealed again and is then polished for shipping. During each annealing, the temperature is reduced to work harden the case for higher tensile strength and elasticity. The final annealing is to the body of the case and is at a lower temperature, so it won’t affect the case head hardness.
While the draw process is capable of mass production, it is not able to easily produce consistent case head hardness, case weight, case volume, and case concentricity. At RCC Brass™ we have taken those variables out of the manufacturing process as we have our C260 cartridge brass hammer-forged into a tight molecular grain structure with high tensile strength and 15% elasticity. We machine all our cases on CNC lathes and mills and our case weight, case volume, and our case concentricity are the best available in the industry. We don’t anneal the case head as it is hammer forged to a high tensile strength which gives us the same hardness for each case. Since we use CNC equipment to manufacture our reloading brass, case weight is nearly identical, the case volume is too, and our case concentricity is held to a 0.001”.
Since we are not held back by the limitations of a draw system, we are able to use higher strength alloys to manufacture cartridges. Our new C272 brass alloy has a much higher tensile strength and tighter molecular grain structure than C260 brass, without losing the needed elasticity. Test results have been very positive as we’ve had reports of increased in velocity and energy and lower shot deviations versus C260 drawn brass. But the test is what you can do with RCC Brass™ reloading brass products.
