Swedish Bofors L/70 40mm Round

1. Overview

The Bofors L/70 40mm round is a family of 40×364mm ammunition designed for the Bofors 40mm L/70 automatic cannon, one of the most successful and widely deployed medium-caliber anti-aircraft and multi-role weapon systems in modern military history. The L/70 (“Length 70 calibers”—referring to the 70-caliber barrel length) represented a significant improvement over the legendary WWII-era Bofors 40mm L/60 system, offering higher muzzle velocity, greater effective range, and improved accuracy. The 40mm L/70 ammunition family includes High-Explosive (HE), High-Explosive Tracer (HE-T), Armor-Piercing (AP), Target Practice (TP), and modern programmable airburst rounds. Despite sometimes being referenced as a “rifle grenade” in certain databases, the Bofors 40mm L/70 round is correctly classified as automatic cannon ammunition, fired from a rapid-fire naval, ground, or vehicle-mounted weapon system.

Note on Classification: The user’s request references this as a “Rifle Grenade.” This is a misclassification likely stemming from database categorization. The Bofors 40mm L/70 round is automatic cannon ammunition, not a rifle grenade. It is fired from dedicated automatic weapon systems, not from a rifle or rifle adapter.

2. Country/Bloc of Origin

  • Country of Origin: Sweden
  • Developer/Manufacturer: AB Bofors (now part of BAE Systems Bofors)
  • Period of Development: The L/70 system was developed in the late 1940s and entered service in 1951; ammunition development has continued through to the present day
  • International Production: Licensed production and derivative manufacture in numerous countries including the United States, United Kingdom, Italy, India, South Korea, Japan, and others
  • Export History: One of the most widely exported weapon systems in history; adopted by over 60 nations across NATO, non-aligned, and developing countries
  • U.S. Designation: The L/70 system is designated as the M1 (ground mount) in U.S. Army service; ammunition carries corresponding U.S. “M” designations

3. Ordnance Class

  • Type: 40mm automatic cannon ammunition (40×364mmR)
  • Primary Roles:
    • Anti-aircraft (AA): Primary designed role—engaging low-to-medium altitude aircraft and helicopters
    • Multi-role: Ground targets, naval targets, light armored vehicles, and anti-surface engagements
    • Modern application: Counter-UAV, counter-rocket/artillery/mortar (C-RAM), and force protection
  • Delivery Method: Fired from the Bofors 40mm L/70 automatic cannon in towed, self-propelled, naval, and vehicle-mounted configurations
  • Category: Medium-caliber automatic cannon ammunition

4. Ordnance Family / Nomenclature

  • Cartridge Designation: 40×364mmR (the “R” denotes a rimmed cartridge case; this distinguishes L/70 ammunition from L/60 ammunition, which uses the 40×311mmR cartridge)
  • Common Round Types:
    • HE (High Explosive): Standard anti-aircraft and area-effect round with impact fuze
    • HE-T (High-Explosive Tracer): HE round with a tracer element for visual tracking
    • PFHE (Pre-Fragmented High Explosive): Enhanced fragmentation round with pre-formed fragments
    • 3P (Programmable, Proximity, Point-detonation): Modern multi-mode programmable fuze round by BAE Systems — capable of airburst, proximity, and impact modes
    • APFSDS-T (Armor-Piercing Fin-Stabilized Discarding Sabot – Tracer): Anti-armor round for engaging armored vehicles
    • TP (Target Practice): Inert training round matching ballistic characteristics
    • TP-T (Target Practice – Tracer): Training round with tracer
  • U.S. Designations (selected):
    • M811 (HE-T)
    • M822 (TP-T)
    • Various other “M” designations for specific configurations
  • Critical Distinction: 40×364mmR (L/70) ammunition is NOT interchangeable with 40×311mmR (L/60) ammunition or with 40×53mm grenade launcher ammunition (Mk 19). These are completely different cartridges despite sharing the 40mm bore diameter.
  • Common Names: “Bofors 40mm,” “L/70 round,” “forty mike-mike” (colloquial, shared with other 40mm systems)

5. Hazards

  • Primary Hazards:
    • Blast: HE variants contain a significant explosive charge producing a lethal blast radius at the point of detonation
    • Fragmentation: HE and PFHE rounds produce high-velocity fragments lethal to personnel and damaging to equipment over a considerable radius; PFHE variants contain pre-formed fragments designed for maximum lethality against aircraft and personnel
    • Kinetic Energy: AP and APFSDS-T rounds deliver concentrated kinetic energy capable of penetrating light to medium armor
    • Tracer Hazard: Tracer-equipped rounds contain a pyrotechnic composition that burns at very high temperatures; tracer residue can ignite fires
    • Propellant: The large cartridge case contains a substantial propellant charge that is flammable and can detonate under extreme conditions (fire, sympathetic detonation)
  • Sensitivity Considerations:
    • HE rounds with impact fuzes may be extremely sensitive to handling in a dud or partially armed state
    • Modern programmable fuzes (3P) contain electronic components and batteries that may be in unpredictable states
    • The cartridge case may contain residual propellant even in fired cases
    • Primers are sensitive to impact and heat
  • Environmental Stability:
    • Brass or steel cartridge cases resist corrosion well under most conditions
    • The projectile body (steel) will corrode over time, potentially exposing explosive fill
    • Rubber or plastic seals around the fuze may degrade, allowing moisture infiltration
  • UXO Considerations:
    • 40mm L/70 dud rounds are commonly encountered in and around military ranges, former air defense positions, and naval gunnery practice areas
    • Anti-aircraft engagements disperse rounds over wide areas; duds may be found far from the firing position
    • Self-destruct fuzes on some variants reduce but do not eliminate dud hazards
    • All 40mm projectiles, including training variants, should be treated as potentially hazardous until confirmed safe

6. Key Identification Features

  • Dimensions:
    • Cartridge Overall Length: Approximately 522mm (20.6 in) — this is a very large round, significantly bigger than small arms ammunition
    • Projectile Diameter: 40mm (1.57 in)
    • Cartridge Case Length: 364mm (14.3 in)
    • Case Rim Diameter: Approximately 48mm (1.89 in) — the rim is a key identifying feature
  • Weight:
    • Complete Round: Approximately 2.4 kg (5.3 lbs) depending on variant
    • Projectile Weight: Approximately 0.87–0.96 kg (1.9–2.1 lbs) for HE variants
  • Shape:
    • Cartridge case: Long, tapered brass or steel case with a prominent rim at the base (characteristic of the L/70 family)
    • Projectile: Ogival (streamlined) nose profile with a rotating band around the body for barrel engagement
    • Overall: Distinctive fixed-ammunition configuration (projectile permanently crimped to the cartridge case)
  • Color and Markings:
    • HE/HE-T: Projectile body painted yellow (NATO standard for HE); some nations use other conventions
    • AP/APFSDS-T: Projectile body painted black (NATO standard for armor-piercing)
    • TP: Projectile body painted blue (NATO standard for practice/inert)
    • Tracer: Indicated by a red or orange band or tip
    • Cartridge case: Typically natural brass finish or dark-coated steel; stamped with headstamp markings including manufacturer, caliber, lot number, and year
    • Modern 3P rounds: May have distinctive fuze appearance and additional electronic fuze markings
  • Distinctive External Features:
    • Rimmed cartridge case: The prominent rim at the base of the case is a key identifier distinguishing L/70 (40×364mmR) from L/60 (40×311mmR) ammunition
    • Rotating band: A copper or gilding-metal driving band around the projectile body for rifling engagement
    • Fuze at the projectile nose: Visible impact fuze, proximity fuze, or programmable fuze assembly depending on variant
    • Crimp: The projectile is crimped into the case mouth

7. Fuzing Mechanisms

The fuze type varies significantly by round variant:

Standard HE/HE-T Rounds

  • Type: Nose-mounted point-detonating (PD) impact fuze with optional self-destruct
  • Arming: Centrifugal (spin) arming—the fuze arms after the projectile has traveled a safe distance from the muzzle and achieved sufficient rotational velocity
  • Functioning: On impact, the fuze initiates the explosive fill; superquick mode provides instantaneous detonation
  • Self-Destruct: Many variants include a pyrotechnic self-destruct element that detonates the round after approximately 8–12 seconds of flight if no impact occurs, preventing rounds from falling to the ground as UXO (important for air defense use over populated areas)

3P (Programmable) Fuze Rounds

  • Type: Electronic multi-mode programmable fuze developed by BAE Systems
  • Modes:
    • Airburst (ABM): The fuze is programmed at the muzzle by an induction coil setter to detonate at a precise distance/time, creating an optimal fragmentation pattern at the target
    • Proximity: The fuze detects a target using a radar or other sensor and detonates at optimum distance
    • Impact (PD): Standard point-detonation on contact
    • Delay: A brief delay allows penetration of light structures before detonation
  • Programming: The fuze is programmed by an electronic fuze setter at the muzzle of the gun as the round is fired; no manual pre-setting is required
  • Power Source: Internal battery activated during firing
  • Self-Destruct: Electronic self-destruct and self-neutralization features ensure the round does not persist as UXO

APFSDS-T Rounds

  • Type: No explosive fuze; the armor-piercing projectile relies on kinetic energy for penetration
  • Functioning: The sabot discards after leaving the muzzle; the sub-caliber penetrator impacts the target at extremely high velocity
  • Tracer: A pyrotechnic tracer element burns for visual tracking

8. History of Development and Use

The original Bofors 40mm L/60 was developed in the 1930s and became the most important light anti-aircraft gun of World War II, used by virtually all Allied nations. After the war, the increasing speed of jet aircraft demanded a higher-performance weapon. Bofors responded with the L/70 in the late 1940s, featuring a longer barrel (70 calibers vs. 60), higher muzzle velocity (1,005 m/s vs. 881 m/s for the L/60), and a new, more powerful cartridge—the 40×364mmR.

Cold War Adoption: The L/70 system entered service in 1951 and was rapidly adopted by NATO and non-aligned nations as a primary short-range air defense (SHORAD) system. It was deployed in towed, self-propelled, and naval configurations. Notable platform integrations include:

  • BOFI (Bofors Optronic Fire-control Instrument) system
  • Bofors Trinity self-propelled air defense system
  • Naval mounts on corvettes, frigates, and patrol vessels worldwide
  • CV9040 infantry fighting vehicle (Sweden) — using a modified L/70 variant

Combat History: The Bofors 40mm L/70 and its ammunition have been used in numerous conflicts including:

  • Indo-Pakistani Wars (1965, 1971)
  • Vietnam War (naval and ground defense applications)
  • Falklands War (1982) — Argentine L/70 systems engaged British aircraft
  • Iran-Iraq War (1980–1988)
  • Gulf War (1991)
  • Various African and Asian conflicts
  • Ukraine conflict (2022–present) — L/70 systems remain in active use

Modern Evolution: The development of the 3P programmable round by BAE Systems transformed the L/70 from a traditional ballistic weapon into a precision system capable of airburst, proximity, and impact effects. This has given the aging platform new relevance in modern roles including counter-UAV and C-RAM (Counter-Rocket, Artillery, Mortar) missions.

Current Status: Still in active service in over 40 nations; the 3P ammunition program continues to extend the platform’s operational life. New-production L/70 systems are offered by BAE Systems Bofors, and ammunition production remains active worldwide.

9. Technical Specifications

SpecificationDetail
Cartridge40×364mmR (rimmed)
Cartridge Overall Length~522mm (20.6 in)
Projectile Diameter40mm (1.57 in)
Complete Round Weight~2.4 kg (5.3 lbs)
Projectile Weight (HE)~0.87–0.96 kg (1.9–2.1 lbs)
Explosive Fill (HE)~110g (3.9 oz) TNT, RDX, or Comp A equivalent
Muzzle Velocity~1,005 m/s (3,297 ft/s)
Maximum Range~12,500 meters (7.8 miles)
Effective AA Ceiling~3,000–4,000 meters (9,800–13,100 ft)
Rate of Fire240–330 rounds per minute (cyclic)
Self-Destruct Time~8–12 seconds (variants with SD fuze)
APFSDS PenetrationClassified; capable of defeating light to medium armored vehicles

10. Frequently Asked Questions

Q: Is the Bofors 40mm L/70 round a rifle grenade? A: No. The Bofors 40mm L/70 round (40×364mmR) is automatic cannon ammunition fired from the Bofors L/70 weapon system. It is not a rifle grenade, nor is it related to 40mm grenade launcher ammunition (40×46mm low-velocity or 40×53mm high-velocity). The classification as “rifle grenade” in some databases is an error. These three 40mm ammunition types are completely different and not interchangeable in any way.

Q: What is the difference between 40mm L/70 (40×364mmR) and 40mm L/60 (40×311mmR) ammunition? A: Although both are 40mm Bofors rounds, they are not interchangeable. The L/70 cartridge (40×364mmR) is significantly longer and more powerful, producing higher muzzle velocity and greater range. The cartridge cases are different lengths (364mm vs. 311mm), and the overall cartridge dimensions prevent loading L/70 ammunition into an L/60 gun and vice versa. This is a critical safety distinction.

Q: How does the 3P programmable round work? A: The 3P (Programmable, Proximity, Point-detonation) round features an electronic fuze that is programmed at the muzzle by an induction fuze setter as the round passes through during firing. The fire control system calculates the optimal detonation point and transmits this data to the fuze in the milliseconds before it leaves the barrel. The round can then detonate at a preset distance/time (airburst), when it senses a target (proximity), or on impact. This makes it devastatingly effective against UAVs, missiles, and exposed personnel.

Q: Why does the L/70 use a rimmed cartridge case? A: The rimmed design (indicated by the “R” in 40×364mmR) facilitates reliable extraction from the weapon’s chamber after firing. In automatic weapons operating at high cyclic rates, positive rim extraction is highly reliable. The rim also provides a positive headspace reference. This design choice dates to the original Bofors 40mm L/60 and was retained in the L/70 for its proven reliability.

Q: What makes 40mm L/70 UXO dangerous? A: Despite self-destruct features on many modern variants, older HE rounds without self-destruct and rounds where the SD mechanism failed persist as UXO. The projectiles contain sufficient explosive to be lethal, the impact fuzes may be in a partially armed state, and tracer compounds remain incendiary. Additionally, anti-aircraft fire disperses rounds over very wide areas, making UXO from AA engagements difficult to locate and clear. Practice ranges are particular areas of concern.

Q: How many countries currently use the Bofors 40mm L/70 system? A: Over 40 countries currently operate L/70 systems in various configurations. The weapon’s longevity is a testament to its effective design and the continuous modernization of its ammunition, particularly the 3P round, which has given the platform renewed relevance against modern threats like small UAVs and precision-guided munitions.

Q: Can L/70 ammunition be identified by its headstamp? A: Yes. The base of the cartridge case bears a headstamp stamped into the brass or steel, typically showing the manufacturer’s code, caliber designation (40mm), lot number, and year of manufacture. Different manufacturers (Bofors/BAE, Nammo, General Dynamics, Diehl, etc.) have distinctive codes. The headstamp is one of the most reliable methods for identifying ammunition origin, manufacturer, and age.

⚠️ SAFETY WARNING: All ordnance and ordnance components should be considered dangerous until rendered safe by qualified EOD personnel. Never handle, move, or attempt to disassemble any munition. Report all suspected ordnance to appropriate military or law enforcement authorities immediately. This material is for professional educational and identification training purposes only.