Cutaway models of some 25x137mm catridges. These cartridges are mainly used in the Oerlikon KBA-BO2 and the Bushmaster M242 chaingun automatic cannon series.
This gun was based on the 25mm gun produced by the TRW company in the USA. The concept was designed in 1964 by Eugene stoner and used a rotating bolt lock. The weapon was meant for the Bushmaster trials, but the weapon was also extensively tested in Europe as the TRW 6425. When the Bushmaster project was postphoned due to the Vietnam war , Oerlikon took over the European patens rights for the gun.
Development and modifications took place; the weapon was changed from recoil operated to gas operated. It was the first weapon to have a dual feed sysytem incorperated , allowing it to change the ammo type –High explosive to Armour piercing f.i.-.
The Oerlikon manufactured gun is known as the KBA-BO2, optimised for use in APC’s, IFV’s and scout vehicles. The Dutch YPR-PRI armoured personel carrier uses the KBA-BO2 gun in it’s GBI-A01 turrets.
The USA development ended up in the M242 Bushmaster chaingun. The term chaingun is derived from the use of a roller chain that drives the bolt back and forward. Unlike most automatic guns the M242 does not depend on gas operated recoil , it uses a 1.5 Hp (750 Watt) DC motor, positioned in the receiver to drive the chain and dual feed system. This system uses sprockets and extractor grooves to feed, load, fire, extract, and eject rounds. The M242 Bushmaster is for instance used on the M2 Bradley infantery fighting vehicle. More developments around this same cartridge are the French 25x137 Giat M811 gun, the Gau-12 Equilizer gatling gun (USA). The US navy uses the Gun as the Mk38 automatic gun. Cartridges for these guns are interchangable.
HE-T-SD (High explosive- Tracer- Self Destruct) of Dutch manufacture (EMZ / Eurometaal Zaandam). Type designation unknown. The fuze uses the “disc type” mechanical self destruct device (see drawing). Below this disc, a rolled up steel tape (like a serpentina roll) prevents the firing pin from moving down and froms the barrel safety; upon firing the centrifugal force unrolls the “serpentina roll, enabeling the firing pin to pass. The centrifugal arming ball houses the firing cap, however the firing cap is set “out of line” with the firing pin. Only after firing the projectile, the centrifucal force rotates the ball in line with the centerline of the projectile and firing pin. The ball itself is fixed in it’safe position by a copper “horseshoe” (transport safety), clamped over a groove in the lower part of the ball. Only after firing , the centrifugal force bends open the “horse shoe” releasing the ball to rorate.
HEI- SD (High explosive Incendiary- Self Destruct). Cartridge of Swiss design and manufacture. It is meant to be used against soft skinned targets, helikopters, enemy personel and fire positions. The nose fuze has a mechanical self destruct mechanism.
HE-T M-DN-81 High Explosive –Tracer type M-Dn 81. The cartridge is designed an produced by Diehl (Germany). The projectiel is of the Semi Armout piercing type, the reason why it has a base fuze. Above the explosive charge a pressed charge of zirconiumpowder is placed which acts as an incendiary charge.
The lower part of the fuze uses the “disc type” mechanical self destruct device (see pict). Above this, the delay mechanism is placed. This exists of a small aluminium bushing with small balls placed in it. If the bushing moves forward upon impact on the target the balls move outward into a groove, so delaying the spring loaded firing pin in it’s action. This bushing is kept axially fixated by a horse shoe shaped clamp that bends open through centrifugal force after firing, releasing the bushing to move. Above this mechanism, a rolled up steel tape (like a serpentina roll) prevents the firing pin from moving up and froms the barrel safety; upon firing the centrifugal force unrolls the “serpentina roll, enabeling the firing pin to pass. The centrifugal arming ball houses the firing cap, however the firing cap is set “out of line with the firing pin. Only after firing the projectile, the centrifucal force rotates the ball in line with the centerline of the projectile and firing pin. The ball itself is fixed in it’safe position by a copper “horseshoe”, clamped over a groove in the upper part of the ball. Only after firing, the centrifugal force bends open the “horse shoe” releasing the ball to rotate. A second ball safety exits of two pins, one radialy placed, retaining the ball, the second -axial- one blocks the radial one. Only after firing the set back force moves the axial pin down, releasing the radial pin to move outward, releasing the ball.
M792 HEI-T (High Explosive Incendiary –Tracer). A cartridge of US origin. The projectile is filled with 32 grams of Hexal and fuzed with nose fuze M758with mechanical self destruct mechanism. It is meant to be used against soft skinned targets, helikopters, enemy personel and fire positions. V0: 1100 mtrs sec.
APFSDS-T (Armour Piercing Fin Stabilized Discarding Sabot –Tracer), produced by Oerlikon. A tungsten cardide penetrator with an aluminium windshield, surrounded by plastic sabots and a plastic windshield. V0: 1440 mtrs/sec. Penetration: 36mm @60degr @1000 mtrs. , 31mm @60degr. @2000 mtrs.
APDS-T , (Armour Piercing Discarding Sabot- Tracer) made by Oerlikon. Dutch name: Ctg (cartridge) No.:113. A tungsten carbide core surrounded by plastic sabots. Vo: 1335 mtrs/sec. Penetration: 30mm @60 degr. @1000 mtrs., 25mm @60 degr. @2000 mtrs.
APDS-T (Armour Piercing Discarding Sabot- Tracer), produced by NWM. Instead of the black plastic sabots as used with the Oerlikon cartridge (06) this cartridge uses a straight body with hard nylon sabots. Penetration will be appoximately the same as the Oerlikon type (No.06).
TPDS (Target Practice Discarding Sabot. Practice APDS-T cartrige for medium ranges of Dutch manufacture (NWM).
TPDS (target Practice Discarding sabot), practice APDS-T cartrige for medium ranges of Dutch manufacture (EMZ). In the Dutch nomenclature: Ctg No.125.
Practice medium range Linked, cartridge No.127, practice APDS-T cartrige for medium ranges of Dutch manufacture (EMZ).
Sabot test. An experimental NWM projectile, supposedly to test the lower aluminium sabot.
TP-T (Target Practice –Tracer) Ctg (cartridge) No.114, produced by EMZ. A steel projectile body, filled with inert resign. The dummy nosefuze is made of aluminium.
Break up. Short range practice with weapon functioning under full working pressure. A dutch invention. Exists of a thin plastic body, filled with steel powder. Shortly after leaving the barrel, centrifugal forces throw the steel powder outward, ripping open the plastic body. The plastic body remains and the steeldust drop to the ground at appr 10 to 20 mtrs before the barrel.
Unknown cartridge. Most probably a short range practice APFSDS projectile. Shellcase with EMZ base stamping.
Blank cartridge. The body is made of black PVC, the base is made of brass. Stamped in base text: 02-BF-00. Country of origin unknown.
Drill cartridge M86 B3. The lower part is a normal shellcase, the middle part is made of white nylon, the dummy fuze is made of aluminium. Country of origin unknown.
Regards , DJH