Overview
C260 cartridge brass is the deep-drawing brass — 70% copper, 30% zinc, single-phase alpha, the chemistry the metallurgy of brass converged on in the 19th century as offering the optimum balance of strength, ductility, and formability. The Cu-Zn phase diagram has a wide single-phase alpha region up to ~37.5% Zn; the 70/30 composition sits near the upper end of single-phase alpha (~70% Cu / 30% Zn), where ductility is high enough for severe deformation and strength enough to handle service loads after drawing.
The “cartridge” name reflects 150 years of ammunition history. Brass cartridge cases — Boxer-primed centerfire ammunition designed by Edward Boxer (UK) and Hiram Berdan (US) in the 1860s — depend on the case material’s ability to be cup-and-drawn from flat strip into deep thin-walled tubular geometry, hold pressure during firing (~50,000+ psi in modern centerfire rifle cartridges), spring back from chamber walls to permit extraction, and be reformed through multi-step drawing without intermediate failure. The 70/30 brass chemistry hit all of these targets and became the standard ammunition case material for ~150 years, only recently giving ground to steel and aluminum cases for some commercial calibers (steel for cost, aluminum for some training/match ammunition).
Beyond ammunition, C260 is the brass of choice wherever yellow color, polishability, and deep drawability matter together — decorative hardware, lighting, lamp fittings, plumbing trim (the visible bits, not pressure-bearing components), and consumer goods.
Brass alloy selection logic
C260 is one alloy in a family of brasses with overlapping properties:
| Alloy | Cu % | Zn % | Other | Notes |
|---|---|---|---|---|
| C220 Commercial Bronze | 90 | 10 | — | Brass-colored but called bronze; jewelry, ammo gilding |
| C230 Red Brass | 85 | 15 | — | “Red brass” plumbing — actually 85/15 brass |
| C260 Cartridge Brass | 70 | 30 | — | The deep-drawing brass — this entry |
| C268 Yellow Brass | 66 | 34 | — | Slightly more zinc; similar use to C260 |
| C272 Yellow Brass | 65 | 35 | — | Approaching alpha-beta boundary |
| C280 Muntz Metal | 60 | 40 | — | Alpha-beta — hot-formable only |
| C360 Free-Machining | 61.5 | 35.5 | 3 Pb | Adds lead for chip control |
| C385 Architectural | 56-60 | 38-42 | 2-3 Pb | Architectural extrusion |
| C443 Admiralty Brass | 71 | 28 | 1 Sn | Tin-modified for marine |
| C464 Naval Brass | 60 | 39.25 | 0.75 Sn | Marine alpha-beta brass |
Selection logic:
- Need to deep draw brass to a complex form: C260
- Need to machine brass: C360 (lead) — color identical
- Need dezincification resistance in water: C26130 or low-Pb lead-free brass like C46500/C46300
- Need marine immersion service: C443 admiralty or C464 naval
- Need architectural extruded shapes: C385 or C377
The trap is over-specifying C260. For machined parts, C360 is the right choice — same color, vastly better machinability, ~10% cost premium. For pressure-bearing water plumbing, lead-free low-Pb brasses (C46500, C49250) have replaced C260 in modern US Reduction of Lead in Drinking Water Act-compliant plumbing.
Season cracking: the classic alpha-brass failure mode
The most distinctive brass failure is season cracking — spontaneous stress corrosion cracking of cold-worked brass exposed to ammonia or ammonium vapors. The mechanism: cold work introduces residual tensile stress in the alloy; ammonia attacks the alpha brass at grain boundaries; the combination causes intergranular cracking with no applied load required.
The historical naming is delightful: British Army cartridges in India, stored in stables, developed cracked cases during the monsoon (“rainy season”). Investigation in the 1880s–1890s identified ammonia from horse urine + monsoon humidity as the causal factor, and the phenomenon was named “season cracking” after the seasonal climate correlation.
Modern relevance:
- Ammunition manufacturing — stress relief at 250–300°C after final draw eliminates residual stress that would otherwise crack cases in storage
- Refrigeration — ammonia (NH₃ R-717) is a common industrial refrigerant; brass not appropriate
- Wastewater — sewer environments contain ammonia from urine decomposition; brass fittings vulnerable
- Agricultural — fertilizer chemistry releases ammonia; brass hardware near anhydrous ammonia tanks especially at risk
- Laboratory — ammonia and amine reagents
The fix is straightforward: stress-relieve cold-formed brass at 250–300°C (below recrystallization, so the cold-work strength is preserved). This is mandatory for any C260 part that will see ammonia exposure in service.
Dezincification
The second major brass failure mode is dezincification — selective loss of zinc from the alpha brass matrix, leaving porous spongy copper. Mechanism: zinc dissolves in the corroding electrolyte; the remaining copper redeposits but in spongy, mechanically weak form. Result: brass plumbing fitting that looks intact externally but is internally compromised.
Conditions that promote dezincification:
- Stagnant water (low flow)
- Soft water (low calcium / low buffer capacity)
- Acidic water (low pH)
- Chloride-bearing water (slightly brackish)
- High temperature (hot water)
- Long service (years)
Dezincification of plumbing brass is a major historical building maintenance issue — pinhole leaks in old residential plumbing, typically traced to dezincification of C260 or C268 fittings.
Solutions:
- Use C26130 (arsenical brass) for water service — the As addition inhibits dezincification by mechanisms still debated in the metallurgical literature
- Low-lead lead-free brasses (C46500, C46300, C49250, C87500) for modern US Reduction of Lead in Drinking Water Act compliance — typically also dezincification-resistant
- Avoid C260 for pressure-bearing water service entirely in jurisdictions requiring lead-free compliance
Welding considerations — usually avoid
C260 brass can be welded but rarely should be. Two reasons:
-
Zinc fume hazard. Zn boils at 907°C — well below the brass melting point (~915°C liquidus). Any fusion welding vaporizes Zn, generating ZnO fume that causes “metal fume fever” (flu-like illness with fever, chills, muscle aches) in exposed workers. Respiratory protection mandatory.
-
Hot shortness. Brass loses ductility in the 400–800°C range, causing solidification cracking in the weld zone. Skilled operators with appropriate filler and technique can produce acceptable welds, but the process window is narrow.
The much better joining options for brass:
Silver brazing (BAg-1, BAg-2, BAg-7 alloys at 600–800°C):
- Lower temperature than welding, no zinc fume
- Strong joints (often stronger than parent in soft tempers)
- Color-match acceptable for most applications
- Standard joining method for brass plumbing, decorative hardware, and instrument fittings
Soft soldering (Sn-Pb historically, lead-free Sn-Cu / Sn-Ag-Cu modern):
- Easy, low-skill, low-stress joints
- Standard for decorative and electrical brass assemblies
- Limited strength (~30 MPa typical) — not for structural service
For welded brass assemblies in production (rare), ERCuZn-A or RBCuZn-A filler with gas-shielded arc, helium shielding (high heat input), preheat for thick sections, and full respiratory protection for operators. Realistically, redesign for brazed or soldered joining is the right path for almost all brass assembly.
Machining notes
C260 brass machines acceptably but not well. The zinc content makes it less gummy than pure copper, but the 30% Zn alpha brass still has poor chip behavior compared to free-machining alternatives. Production recipe:
- Sharp uncoated or polished-edge carbide
- Speed 200–400 SFM
- Feed 0.005–0.015 in/rev
- Generous positive rake
- Water-soluble or sulfur-bearing cutting fluid
The production answer for machined brass parts is C360. Cartridge brass and free-machining brass have indistinguishable visual color and corrosion behavior in most service environments; the lead content in C360 (3% Pb) transforms chip behavior. Machinability ratings: C260 = 30, C360 = 100 (the reference). For a screw-machine production part where the form is machined, C360 cuts cycle time by 60–70% versus C260.
Reserve C260 for parts that are deep-drawn, spun, hammered, or formed rather than machined. The conventional rule: form C260, machine C360.
Applications by industry
- Defense and ammunition — cartridge cases, primer cups, primer anvils, projectile gilding (C220 commercial bronze is more common for bullet jackets in some calibers). Modern non-brass alternatives (steel, aluminum, polymer) are eroding the historical brass case monopoly for cost reasons.
- Decorative hardware — door knobs, hinges, kick plates, push plates, mail slots, ornamental cabinet hardware. The yellow brass finish is the dominant decorative metallic for traditional and some modern hardware.
- Plumbing trim — escutcheons, decorative flanges, faucet handles. NOT pressure-bearing components in modern lead-free plumbing.
- Lighting — lamp shells, sockets, finials, decorative ceiling rosettes. Brass + lacquer is the standard “antique brass” finish.
- Automotive (legacy) — radiator cores and brass radiator side tanks for older vehicles. Modern automotive radiators are aluminum-plastic; brass radiators persist in heavy equipment, industrial vehicles, and classic-car restoration.
- Musical instruments — cymbals (though some prefer C220 or specialty alloys), horn valve casings, fittings. Sax bodies are typically yellow brass (close to C260).
- Consumer products — deep-drawn brass tins for premium packaging, decorative containers, novelty cases. Premium spice containers, brass beverage cups.
- Marine (above waterline) — decorative trim on yachts and recreational boats. Below-waterline service uses naval brass C464 or admiralty brass C443.
- Watchmaking — watch cases and components (though stainless and titanium are dominant in modern watch industry).
- Jewelry — costume jewelry (gold-plated brass), brass-and- copper artistic jewelry.
Failure modes worth designing around
Season cracking — the dominant brass failure mode. Stress relieve any cold-worked brass at 250–300°C before service in environments with ammonia exposure (animal husbandry, sewage, refrigeration, agricultural, laboratory).
Dezincification — water service failure. Use C26130 arsenical brass or lead-free dezincification-resistant alternatives for plumbing.
Mercury embrittlement — direct mercury contact causes brittle fracture. Brass never appropriate for mercury service. Historical documented industrial accidents.
Acetic acid attack — vinegar, pickle, salad dressing service. Brass not appropriate.
Patina formation — yellow brass dulls to brown over months to years. Lacquer for preservation, or accept the natural aging. Some “antique brass” finishes deliberately accelerate the patina chemically.
Galvanic corrosion of mating metals — brass is cathodic to aluminum, zinc, magnesium, and steel. Isolate in mixed-metal assemblies.
Hot shortness in welding — use brazing or soldering instead.
Zinc fume hazard in any high-temperature operation — welding, hot-cutting, grinding heat. Respiratory protection mandatory.