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Military Multiplex Cartridges
Daniel Watters' Compendium of Little-Known Loadings
5.56x45mm/5.56 NATO
In November of 1962, Frankford Arsenal loaded a small quantity of .223 Duplex cartridges. This consisted of a forward bullet of 33 grains followed by a second 34 grain projectile. The velocity is quoted as 2,760fps.

During the late '60s, Frankford Arsenal experimented with the Low Noise Duplex Cartridge (LNDC). The earliest cartridges were loaded with a pair of 110 grain tungsten core slugs. The initial projectiles use a blunt round nose profile, but later efforts consist of a semi-spitzer shape.

During the late 1980s, Olin produced duplex 5.56x45mm ammo for Colt's entry in the Advanced Combat Rifle (ACR) trials. The two projectiles weighed 35 grains (front) and 33 grains (rear), giving a velocity of ~2900fps. The Bodermansports.com website claims to have some of the ACR test ammo available.

.22/7.62x51mm (Experimental):
"Project SALVO" - The experimental .22/7.62x51mm (aka: .22 NATO) cartridge used a standard length case for the single projectile load. However, its pair of duplex variants were loaded in long-neck cases. One was with loaded with two 35 grain projectiles (3505fps) while the other was loaded with a pair of 41 grain bullets (3250fps).

.22/.30'06 (Experimental):
During SALVO II testing, a duplex .22-'06 cartridge was introduced. It used a long neck case holding a pair of 50 grain projectiles (2975fps).

6.35mm Frankford/Winchester SCHV (Experimental):
Dr. Carten's brief sidetrack for an "optimum" 6.35mm SCHV cartridge also produced duplex variants. The 6.35mm cartridge cases were dimensionally similar to the .25 Remington. One case was left full-length (~2.08") and loaded with 70 grain projectiles for both single and duplex loads. The slightly shorter case (~1.88") was loaded with single 70 grain projectiles or a pair of 53 grain bullets for the duplex (2,600fps). The single projectile loads were the FA-T124 (long) and FA-T116 (short). The duplex loads were the FA-T127 and FA-T115.

.25/7.62x51mm (Experimental):
"Project SALVO" - Experimental .25 caliber cartridges were also based on the 7.62x51mm case, with single projectile and duplex loadings. The duplex loads featured a pair of 61 grain projectiles @ 2990fps. Once again, the case lengths are different between the single projectile and duplex loads.

.27/7.62x51mm (Experimental):
"Project SALVO" - Experimental .27 caliber cartridges were also based on the 7.62x51mm case, with single projectile and duplex loadings. The duplex loads featured a pair of 71 grain projectiles @ 2980fps. Yet again, the case lengths are different between the single projectile and duplex loads.

7.62x51mm NATO:
"Project SALVO" - An early duplex 7.62x51mm cartridge used a pair of 96 grain projectiles (2560fps) in a long necked case. However, the later T314E3 duplex load used a standard case. This was eventually type-classified as the M198 Duplex Ball, and is credited with two ~84 grain slugs at 2750fps.

"Salvo Squeezebore" - Used with a special barrel attachment, three 20 grain projectiles would be squeezed down to ~.15", giving a velocity of 4000fps.

"Future Rifle Program" - An off-shoot of their earlier 9.53mm/10mm multiple fl�chette cartridges, Winchester later applied the concept to the standard 7.62x51mm cartridge case. This version launched a trio of 10.2 grain fl�chette via a puller sabot.

.30-40 Krag:
W.R. Scott multiball (duplex) cartridge loaded by Winchester.

Multiball (duplex) guard cartridge (circa 1902) loaded by Frankford Arsenal. The two projectiles appear to be lead buckshot.

.30'03 Springfield:
Multiball (duplex) guard cartridge: The two projectiles, which appear to be lead buckshot, weigh 42 grain each. The cartridge is loaded with 43.5 grains of an unspecified powder. The short overall length of cartridge would not allow it to feed reliably from the magazine. Instead, the cartridge was intended to be manually inserted into the chamber.

.30'06 Springfield:
The W.W. Greener experiments in the UK also played with duplex and triplex loads for the .30'06. The cases were reportedly supplied by Remington, but loaded in the UK. You can see some of the Greener and Project Salvo .30'06 loads here.

"Project SALVO" - There were at least three different multi-projectile loads tested in long-necked .30'06 cases. One used a pair of 110 grain projectiles (2520fps), another had two of 96 grain bullets (2630fps), and the last possessed a trio of 66 grain slugs (2640fps). By the time of SALVO II, the duplex and triplex .30'06 loads used standard cases. There is also mention of a duplex load using two 140 grain bullets, but the configuration is not specified.

.303 British:
Greener Triplex Cartridge (circa 1918) loaded by Kynoch. (There is reportedly Greener Duplex Ammo as well.)

W.R. Scott multiball (duplex) cartridge loaded by Winchester.

.330 Amron Aerojet (8.38x69mm) (Experimental):
Three to four fl�chette are held in a single sabot.

7.92x57mm Mauser:
There were at least three different duplex loads tested by the Germans late in the Second World War. Loaded at Finower Industry (headstamp "cg"), one cartridge used two of the "S Patrone" projectiles, another used one "S Patrone" projectile and a projectile from the 7.92x33mm Kurz Patrone, and the last used two Kurz Patrone projectiles. The later was considered the best, considered effective out to 300 meters. The muzzle velocity is reported at ~1760fps.

9.53mm/10mm Multiple Fl�chette Cartridge (Experimental):
"Future Rifle Program" - In the late '60s, Winchester developed a series of multiple fl�chette cartridges, which launched from three to five fl�chette via a pusher sabot. These cartridges were based on a proprietary straight-wall, belted cartridge case. By late 1970, Winchester finalized a 9.53mm variant using an aluminum cartridge case. The loadings included a standard four fl�chette payload (4,240fps), a pair of 'ball' fl�chette paired with a tracer, and even a specialized armor piercing 'penetrator'. Despite pushing pressures of up to 75,000psi, the large bore volume limited this to a brief spike, allowing the aluminum cartridge case to remain intact.

.45 ACP(?):
"Salvo Squeezebore" - Used with a special barrel attachment, three 80 grain projectiles would be squeezed down to ~.38".

.45-70/.45 Government:
Both Frankford Arsenal and Union Metallic Cartridge (UMC) Company produced triplex multiball loads. The Frankford Arsenal loads used three 133 grain round balls and 45 grains of black powder. Examples of these have been found using a copper case and the Ben�t Cup Inside Primer. The UMC multiball loads are clearly later production with conventional primers and brass cases.

12.7x99mm (.50 BMG):
"Salvo Squeezebore" - Used with a special barrel attachment, five 140 grain projectiles would be squeezed down to ~.30", giving a velocity of 3050fps.

12.7x107mm Soviet:
LVE (Novosibirsk) has offered the following:

Duplex API 1SL: 463 grain (front) and 478 grain (rear) at 2460fps.

Duplex API-T 1SLT: two 416 grain projectiles at 2460fps.

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Originally posted by 'Trapper':
As stated I never saw one. Tony, are you implying this was fired through a regular Bowning 50cal? Also, could you post up a picture of the round?
Best regards,

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The M2 would have needed a squeezebore attachment fitted to the muzzle, but otherwise it was intended to be standard AFAIK. Sorry I have problems with pictures at the moment - I'm off-line at home

Tony Williams: Military gun and ammunition website and discussion
forum