81mm Mortar Ammunition And Fuzes

Gary's U.S. Infantry Weapons Reference Guide

Each cartridge has fins around the tail to stabilize it in flight and to cause it to strike fuze-end first. The propelling charge consists of an ignition cartridge and removable propellant increments. The ignition cartridge (with primer) is fitted into the base of the fin shaft. The removable increments are fitted onto or around the shaft, depending on their type.

• The cartridge is dropped down the barrel, fin-end first.
  
  
• The ignition cartridge strikes the firing pin and detonates, which causes a flash that passes through the radial holes in the shaft.
  
  
• The propellant increments are ignited, which produce rapidly expanding gases that force the cartridge from the barrel.
  
  
• The obturating ring ensures equal muzzle velocities in hot or cold barrels by keeping all the gases in the barrel until the cartridge has fired.
  
  
• When fired, the cartridge carries the ignition cartridge with it, leaving the mortar ready for the next cartridge.

The floating firing pin located within the primer has approximately 1/16 of an inch to move around. This may cause the firing pin to ignite the charges if the cartridge is dropped on the fin end.

Ammunition types:

• High Explosive (HE). Fragmentation and blast. Causes troop casualties and damage to light material.
• Red Phosphorus (RP), White Phosphorus (WP).
Smoke. Used to screen, signal, and act as an incendiary.
• Illumination.
Used to illuminate, signal, and mark.
• Training Practice (TP).
Training items are completely inert. Practice items may or may not contain explosive sections such as propellant charges or spotting charges.

81mm mortar ammunition.

Model	Type	Length	Weight	Minimum - Maximum Range	Effective Bursting Area	Fuze
M1 Sabot	Training	15.618 in (397 mm)	9.6 lb (4.35 kg)	77 - 475 yd (70 - 435 m)	N/A	M744, M745, M746, M747
M43A1	HE	13.32 in (338 mm)	7.15 lb (3.24 kg)	?	?	?
M57A1	WP	22.91 in (582 mm)	12.46 lb (5.65 kg)	? - 2,372 yd (? - 2,169 m)		PD M525
M68	Training	?	?	? - 311 yd (? - 284 m)	N/A	N/A
M301A1, M301A2	ILLUM	?	?	? - 2,351 yd (? - 2,150 m)	500,000 candlepower for 60+ seconds	MT M84
M301A3	ILLUM	?	?	109 - 3,445 yd (100 - 3,150 m)	3,609 ft (1,100 m) diameter 500,000 candlepower for 60+ seconds	MT M84
M362A1	HE	20.80 in (528 mm)	9.42 lb (4.27 kg)	? - 3,957 yd (? - 3,618 m)	?	PD M524, PD M526, VT M532
M370	WP	?	?	? - 3,987 yd (? - 3,646 m)		PD M524, PD M526
M374, M374A1, M374A2	HE	20.80 in (528 mm)	9.34 lb (4.24 kg)	? - 4,921 yd (? - 4,500 m)	?	PD M524, PD M526, PD M567, VT M532
M374A3	HE	?	9.05 lb (4.1 kg)	80 - 5,250 yd (73 - 4,800 m)	112 ft (34 m) diameter	PD M524, PD M526, VT M532
M375, M375A1, M375A2	WP	?	9.12 lb (4.1 kg)	77 - 5,025 yd (70 - 4,595 m)		PD M524, PD M526, PD M567
M375A3	WP	20.80 in (528 mm)	9.34 lb (4.24 kg)	? - 5,250 yd (? - 4,800 m)		PD M524, PD M567
M816	IR ILLUM	25.49 in (647 mm)	9.25 lb (4.2 kg)	?	?	MTSQ M772
M819	RP	25.43 in (646 mm)	10.2 lb (4.63 kg)	328 - 5,331 yd (300 - 4,875 m)	90 to 150 by 30 to 40 meters for 2 to 3 minutes	MTSQ M772
M821	HE	?	10 lb (4.5 kg)	90 - 6,133 yd (83 - 5,608 m)	131 ft (40 m) diameter	M734
M853	ILLUM	?	9.1 lb (4.1 kg)	328 - 5,577 yd (300 - 5,100 m)	3,937 ft (1,200 m) diameter 600,000 candlepower for 1 minute	MTSQ M772, M768
M879 FRPC	TP	19.55 in (497 mm)	9.40 lb (4.3 kg)	?	N/A	PD Practice M751
M880 SRTR	TP	14.57 in (370 mm)	6.84 lb (3.1 kg)	51 - 500 yd (47 - 458 m)	N/A	PD Practice M775
M889	HE	?	10 lb (4.5 kg)	90 - 6,133 yd (83 - 5,608 m)	131 ft (40 m) diameter	PD M935

M1 Sabot

The M1 81mm sabot (inert) consists of two major components: the 81mm aluminum alloy sabot and 22mm subcaliber cartridge. The sabot is designed to fire the subcaliber cartridge through the barrel. The subcaliber cartridge, when loaded into the sabot, approximates a round of service ammunition both in size and weight. The entire assembly is then fired from the mortar just as in service firing.

The subcaliber projectile travels from 230 to 1,427 feet (70 - 435 m), depending on the charge and elevation selected. The projectile emits a puff of smoke and an audible report upon impact, but no fragmentation. At the time of firing, the sabot is also expelled from the mortar and impacts 6.5 to 49 feet (2 - 15 m) from the mortar. It is then recovered, cleaned, reloaded, and refired.

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M57, M57A1 WP

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M68 Training

Cartridge can be re-used.

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M301A1, M301A2 ILLUM

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M301A3 ILLUM

Cartridge has a cylindrical body that contains an illuminating candle and parachute assembly. The round has a burst height of 600 meters and provides illumination for about 60 seconds for an area of about 1,200 meters. It is painted white with black markings. It uses the M185 propelling charge that consists of eight increments fitted into the spaces between the fins and held by a propellant holder. The increments are individually wrapped with waterproof bags that are not removed.

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M362, M362A1 HE

Cartridges are of steel forge construction and contain about 2.10 pounds (0.95 kg) of composition B explosive. They use the M5 propelling charge that consists of eight cloth bags attached to the tail unit. The cartridges are painted olive drab with yellow markings. They are fuzed with the M524-series, M256-series, or M532. Cartridges assembled with the M524 (A1, A2, A3, or A4) fuze are for use by the U.S. Marine Corps and U.S. Navy only.

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M370 WP

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M374, M374A1, M374A2 HE

Cartridges are painted olive drab with yellow markings and are constructed from pearlitic malleable cast iron. They contain about 2.10 pounds (0.95 kg) of composition B explosive. The M374 cartridge is fitted with the M90 propelling charge. The M374A1 and M374A2 cartridges are fitted with the M90A1 propelling charge. Both the M90 and M90A1 propellants are in nine wax-tested, cotton cloth, bag increments assembled to the tail unit. The cartridge can be fitted with the M524-series, M526-series, M567, or M532 fuzes. Those cartridges assembled with the M524 (A1, A2, A3, or A4) fuze are for use by the US Marine Corps and US Navy only.

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M374A3 HE

HE cartridge is constructed from pearlitic malleable cast iron and contains about 2.10 pounds (0.95 kg) of composition B explosive. It uses the M205 propelling charge, consisting of four horseshoe-shaped increments fitted around the tail. The cartridge is painted olive drab with yellow markings. It can be fitted with either the M567, M524, or M532-series fuzes.

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M375, M375A1, M375A2 WP

Cartridges are painted light green with red markings and one narrow yellow band. They are assembled with either an M524-series, M526-series, or M567 fuze. The M375 cartridge uses the M90 propelling charge while the M375A2 and M375A1 cartridges use the M90A1 propelling charge. Cartridges assembled with the M524 (A1, A2, A3, or A4) fuze are for use by the US Marine Corps and US Navy only. This cartridge is ballistically matched to the M374A2, M374A1, and M375 HE cartridges.

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M375A3 WP

Cartridge is ballistically similar to the M374A3 (HE) cartridge. It contains white phosphorus that produces white smoke on contact with air. The cartridge is painted light green and has red markings and one narrow yellow band. The cartridge uses the M205 propelling charge and is assembled with the M567 or M524-series fuze.

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M816 IR ILLUM

The M816 81mm Infrared Illumination Cartridge with Mechanical Time - Super Quick (MTSQ) Fuze is designed for use with the M252 81mm Light Battalion Mortar System, currently fielded to all Light Infantry units in the Army. The round is used to illuminate targets during night operations. Infrared Illumination greatly enhances the effectiveness of night vision devices.

The round consists of a two-piece body filled with illuminating flare, M772 MTSQ fuze and tail assembly. The round is ballistically similar to the 81mm High Explosive (HE) and smoke cartridges.

This is a training standard item used in both training and combat.

Type Classification Date: September 2001. Unit cost: $1,260 (Fiscal Year 2005).

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M819 RP

M252 only. Cartridge has a cylindrical body and contains red phosphorus (RP) that produces white smoke on contact with air. The cartridge uses the M218 propelling charge, which consists of four horseshoe-shaped increments fitted around the tail. The cartridge is painted light green with black markings and one narrow brown band.

This cartridge was modified to prevent out-gassing of phosphine while in storage. Gas Absorbent Modules (GAMS) have been added to rounds in storage to minimize potential exposure to gas.

This is a training standard item and is used both in training and war reserve.

Type Classification Date: December 1986.

Unit cost: $1,146 (Fiscal Year 2007).

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M821 HE

M252 only. A British-made cartridge fitted with the US M734 multioption fuze. It is constructed from ductile cast iron and contains about 1.5 pounds (0.68 kg) of cyclonite (RDX)/trinitrotoluene (TNT) composition explosive. The aluminum tail assembly has six integral fins equally spaced around the rear, which stabilize the round in flight. The cartridge is painted olive drab with yellow markings. Each cartridge weighs about 10 pounds and is provided with the M223 propelling charge, consisting of four horseshoe-shaped increments fitted around the tail.

This is a training standard item used in both training and combat.

Type Classification Date: July 1991.

Unit cost: $605 (Fiscal Year 2007).

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M853 ILLUM

M252 only. Cartridge has a cylindrical body that contains an illuminating candle and parachute assembly. It provides illumination for about 60 seconds with 600,000 candlepower illumination. It is assembled with the M772A1 MTSQ. It uses the M219 propelling charge. The round is range-matched to the 81mm high explosive (HE) and smoke cartridges.

This is a training standard item used in both training and war reserve.

Type Classification Date: December 1986.

Unit cost: $1,635 (Fiscal Year 2007).

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M879 FRPC

The M879 Full Range Practice Cartridge (FRPC) is a US-developed, improved practice round for use in the M252, 81mm Mortar System. The practice cartridge provides realistic training in place of the M821A1/M889A1 High Explosive (HE) Cartridges. The M751 Point Detonating Practice Fuze simulates the M734A1 fuze and can be set, for training purposes, to the required fuze functioning mode for the fire mission. The M751 fuze used on this round detonates upon impact and produces a flash, bang, and smoke signature that gives the forward observer the ability to adjust fire. The M879 Full Range Practice Cartridge consists of a steel body with an inert concrete payload.

Blue with white markings and brown band

This is a training unique item.

Type Classification Date: August 1986.

Unit cost: $453 (Fiscal Year 2007).

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M880 SRTR

The M880 Short-Range Training Round is designed as a training round for the 81mm mortar (M29 and M252) and the 120mm mortar (using the M303 insert). The SRTR is designed to be fired, recovered, refurbished, and refired. The round is fired from the mortar the same as service ammunition. When fired, the SRTR travels from 154 to 1,503 feet (47 - 458 m), determined by charge and elevation. Upon impact, the SRTR emits a flash, bang, and smoke discharge but no fragmentation.

The projectile body is made from cast iron and is machined to accept the M775 fuze, the tail fin, three charge plugs, three dud plugs, and the obturator ring. It is painted blue with white lettering and one brown band to identify it as a practice round. The tail fin assembly is threaded onto the stud at the base of the projectile body. Inside the tail fin is the propellant cartridge - a primed 12-gauge shotgun shell casing loaded with a double base propellant.

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M889 HE

M252 only. Cartridge is of the same construction as the M821 cartridge in every detail except the fuze, which is the M935. The tail assembly and propulsion system will be common to all other 81mm HE and training rounds. This round will be used primarily in training since it is less expensive than the M821A1, the preferred war-fighting round. However, the M889A1 is highly lethal and can be used in combat.

This is a training standard item used in both training and combat.

Type Classification Date: July 1991.

Unit cost: $543 (Fiscal Year 2007).

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Fuze types:

• Point Detonating (PD). All PD fuzes are superquick - detonate on impact.
• Proximity (VT). A proximity fuze is an electronic device that detonates a projectile by means of radio waves sent out from a small radio set in the nose of the projectile.
• Mechanical Time (MT). These fuzes use a clockwork mechanism to delay functioning for a specific time.
• Multioption (MO).
These fuzes have multiple functions (proximity, impact, delay).
• Dummy, Practice.

M84 MT Fuze

• Is a single-purpose, powder-train, mechanical-time fuze used with the 81mm M301A1 and M301A2 illuminating cartridges.
• It has a time setting of up to 25 seconds. The fuze consists of a brass head, body assembly, and expelling charge.
• The fuze body is graduated from 0 to 25 seconds in 1-second intervals; 5-second intervals are indicated by bosses. The 0-second boss is wider and differs in shape from the other body bosses; the safe setting position is indicated by the letter "S" on the fuze body.
• The adjustment ring has six raised ribs for use in conjunction with fuze setter, M25, and a setting indicator rib (marked SET) about half the height and width of the other six ribs.
• Safety before firing is provided by a safety wire, which must be removed just before firing.
• Length: 3.85 in (98 mm).
• Weight: 1.82 lb (0.83 kg).

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M84A1 MT Fuze

• Is a single-purpose, tungsten-ring, mechanical-time fuze used with the 81mm M301A3 illumination cartridge. It has a time setting of up to 50 seconds.
• The fuze consists of a brass head, body assembly, and expelling charge.
• The fuze body is graduated from 0 to 50 seconds in 2-second intervals; 10-second intervals are indicated by bosses. The 0-second boss is wider and differs in shape from the other body bosses; the safe setting position is indicated by the letter "S" on the fuze body.
• The adjustment ring has six raised ribs for use in conjunction with fuze setter, M25, and a setting indicator rib (marked SET) about half the height and width of the other six ribs.
• Safety before firing is provided by a safety wire, which must be removed just before firing.
• Length: 3.85 in (98 mm).
• Weight: 1.82 lb (0.83 kg).

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M524-series PD Fuzes

• Has two function settings: Superquick/impact (SQ/IMP) and delay.
• When set at delay, the fuze train causes a 0.05-second delay before functioning.
• When set at SQ, the fuze functions on point impact or graze contact.
• The fuze contains a delayed arming feature that ensures the fuze remains unarmed and detonator safe for a minimum of 1.25 seconds of flight.
• It arms within a maximum of 2.50 seconds. The safety pull wire is removed just before inserting the cartridge into the mortar.
• Length: 6.01 in (153 mm).
• Weight: 1.27 lb (0.58 kg).

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M525-series PD Fuzes

• Fuze has a booster charge, delay arming mechanism, bore-riding pin, and safety wire.
• Has an SQ/IMP function only.
• Length: 3.53 in (90 mm).
• Weight: 0.44 lb (0.2 kg).

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M526-series PD Fuzes

Fuze consists of a M525 PD Fuze assembled to a boostered adapter. Has an SQ/IMP function only. It is fitted with a safety wire and pin that are removed immediately before firing.

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M532 VT Fuze

• Is a radio doppler fuze that has a proximity (PROX) or SQ/IMP function.
• An internal clock mechanism provides nine seconds of safe air travel (610 to 2,340 meters along trajectory for charge 0 through 9, respectively).
• Once set to act as an impact fuze, the mechanism cannot be reset for PROX.
• The fuze arms and functions normally when fired at any angle of elevation between 0800 and 1406 mils at charges 1 through 9. The fuze is not intended to function at charge 0. However, at temperatures above 32 degrees Fahrenheit and at angles greater than 1068 mils, the flight time is sufficient to permit arming.
• To convert the fuze from PROX to SQ/IMP, the top of the fuze must be rotated 120 degrees (one-third turn) in either direction. This action breaks an internal sheet pin and internal wire, thereby disabling the proximity function.
• Length: 5.98 in (152 mm).
• Weight: 1.28 lb (0.58 kg).

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M567 PD Fuzes

• Is an impact fuze that has a SQ/IMP or D function.
• It comes preset to function on SQ/IMP, and the selector slot should align with the SQ mark on the ogive.
• To set for delay, the selector slot should be rotated clockwise until it is aligned with the "D" mark on the ogive.
• The fuze has a safety wire that must be removed before firing.
• Length: 5.97 in (152 mm).
• Weight: 1.3 lb (0.59 kg).

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M734 MO Fuze

Has four function settings:

1. PRX (proximity) causes the cartridge to explode between 3 and 13 feet above the ground.
2. NSB (near-surface burst) causes the cartridge to explode up to 3 feet above the ground.
3. IM (impact) causes the cartridge to explode on contact.
4. DLY (delay) incorporates a 0.05-second delay in the fuze train before exploding the cartridge.

No tools are needed to set the fuze, and the setting can be changed several times without damaging the fuze. It has no safety pins or wires to reduce preparation time. If the fuze does not function as set, it automatically functions at the next lower setting.

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M751 Practice Fuze

There are two types: type 1 resembles the M734 fuze, and type 2 resembles the M935 fuze. The M751 is fitted with a smoke charge that operates on impact. The safety/packing clip should be removed when the cartridge is unpacked.

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M772 MTSQ Fuze

Is a mechanical time superquick (MTSQ) fuze.

Unit cost: $145 (Fiscal Year 2005).

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M772A1 MTSQ Fuze

Is a mechanical time superquick (MTSQ) fuze. It can be set from 3 to 55 seconds at half-second intervals. The safety wire must be removed before firing.

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M775 PD Practice Fuze

Point detonating practice fuze. Produces a visible flash, a cloud of smoke, and an audible sound on impact for spotting purposes.

Has multi-option type (PRX/NSB/IMP/DLY) dummy settings to simulate an M734 multioption fuze. The M775 PD fuze functions on impact with superquick action only. Setting of fuze is for practice only and has no effect upon actual functioning.

This is a training unique item; not used in combat.

Unit cost: $16 (Fiscal Year 2005).

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M935 PD Fuze

Has two function settings: impact and delay. It is fitted with a standard pull wire and safety pin that are removed immediately before firing.