Brass Stamping: Cartridge Brass, Free-Machining Grades, and Draw Quality

C260 cartridge brass (70% copper, 30% zinc) is the best general deep-draw brass, with roughly 45-55% elongation in the annealed temper, which lets it form deep shells, cans, ferrules, and caps that would split in most other alloys. It earned the 'cartridge' name making deep-drawn ammunition cases. For the deepest parts it is drawn in multiple stages with interstage annealing to restore ductility between draws, since the brass work-hardens as it forms. If your part needs extreme depth, C260 in the soft temper is the answer. Avoid C360 free-cutting brass for any real forming; its lead content makes it machinable but brittle, and it cracks when drawn. Naval brass (C464) forms to moderate bends but not deep draws. So the rule is simple: deep draws and tight forms call for C260, and the harder or leaded grades are for flat blanks and machined features.

C360 free-cutting brass is the most machinable copper alloy made, rated 100% machinability, because it contains lead that fractures chips during cutting. But that lead also makes the alloy brittle in forming: it has low elongation and cracks readily when bent or drawn, so it is genuinely a poor choice for any stamped part with real forming. Its place in stamping is flat blanks that get heavily machined afterward, threading, drilling, turning, where its machinability saves significant secondary-op cost and the forming is minimal. If your part has bends, flanges, or draws, specifying C360 will lead to cracked parts and frustration. The right approach is to use a forming-grade brass like C260 cartridge brass or C268 yellow brass for the formed geometry, and reserve C360 only for parts whose value is in machining rather than forming. Many buyers default to C360 because it is the famous brass, and get surprised at the press.

Season cracking is stress-corrosion cracking in high-zinc brasses, where residual tensile stress left over from cold forming combines with a corrosive agent, classically ammonia or amine vapors, to crack the part over time, sometimes long after manufacture (hence 'season'). Deep-drawn and heavily bent brass parts carry significant residual forming stress and are most at risk. The standard prevention is a low-temperature stress-relief anneal after stamping, typically around 250-300°C, which relaxes the residual stress without fully annealing away the work-hardened temper or distorting the part. This step is routine for drawn shells, marine hardware, and any brass exposed to ammonia-bearing environments. Naval brass and other corrosion-resistant grades help in seawater but do not by themselves eliminate season cracking from forming stress, so the stress relief still belongs in the routing for high-stress parts. Omitting it on heavily formed brass in the wrong environment is a documented cause of field failures.

Brass material costs more than steel but is typically cheaper than pure copper, since the zinc content displaces some of the expensive copper, so brass sits in the middle on raw-material cost, and its price moves with the copper commodity market. Brass's standout economic advantage is its excellent stamping behavior: it forms cleanly with low tooling wear, takes crisp edges with minimal burr and deburring, and draws deep without the multi-station complexity some metals require, all of which lower conversion cost and improve yield. It plates and solders well, keeping finishing straightforward. Like copper, brass scrap has real recovery value, so reputable shops credit it back, and nesting efficiency matters. Tooling follows standard stamping economics, with progressive dies amortizing well over high-volume terminal and hardware runs. Overall, brass often delivers a lower total stamped-part cost than its material price alone would suggest, because the easy forming and clean edges cut secondary-operation expense.