The dark magic of duplex loads??

[Ds J]

Hallo Folks,

FIRST OFF: DUPLEX LOADS ARE UNCHARTED TERRITORY AND SHOULD MOST PROBABLY NOT BE DONE, OR ONLY CONSIDERED VERY CAREFULLY. SINCE IT IS A VERY INTERESTING THEME, I CONTINUE.

Does anyone have experience with duplex loads?

I knew Prof Koos Badenhorst (one of the designers of the 458 Express) and he mentioned that he got higher speeds and lower pressures with a duplex load: if memory serves correct he got the same speed from a duplex load at 40 000 psi where he usually had to go over 50 000psi with a regular load.

I also had contact with an older chap in the southern Namib who has been doing it for years. He got great results as well, but I lost contact with him.

How does it work?   

[oafpatroll]

This is something I find interesting but will not touch with a bargepole. Developing low velocity cast bullet loads from my 270 Win with faster powders that were based on published data made me nervous enough. This black magic demon summoning would make me pee my pants.

[Tripodmvr]

Most of the experimentation was done long ago, before the advent of all the new propellants that are now available.
If we look at Somchem, the only glaring omission is a slow burning propellant for the Magnums i.e. 7mm Rem, 338LM and the other large cased cartridges. S395 was supposed to fill that gap but it never reached production stage.

With the big variety from Hodgon, Vihtavuori, Norma etc. it is just not worthwhile mixing two or three propellants to try and lower pressure and up the speed.

There are many articles on the Net that tells of these experiments. I read one on Casull and his efforts to get his 454 to give better performance. Black powder and modern propellants are also used to try and enhance performance.

[big5ifty]

I know of a 45-70 that made power factor for BASA with duplex loads.

It was a bolt action.

Normal 45-70 loads are too anemic for BASA purposes.

[223]

Duplex loads are often used where the correct burn rate powder is not available.  So you use a duplex load of a faster and a slower powder to get in between the 2.  The exact mix ratio can be carefully controlled.  if you were to mixthe 2 different powders you would probably get erratic results due to variations in the mix.

[Ds J]

Duplex loads are often used where the correct burn rate powder is not available.  So you use a duplex load of a faster and a slower powder to get in between the 2.  The exact mix ratio can be carefully controlled.  if you were to mixthe 2 different powders you would probably get erratic results due to variations in the mix.

How does one calculate these ?

[Treeman]

Duplex loads are often used where the correct burn rate powder is not available.  So you use a duplex load of a faster and a slower powder to get in between the 2.  The exact mix ratio can be carefully controlled.  if you were to mixthe 2 different powders you would probably get erratic results due to variations in the mix.

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I thought duplex powders were used to take full advantage of the powders capabilities, usually along the line of. A slow powder is needed to start a heavy bullet moving, once it is moving a faster powder behind it would be better. So in the micro super speed world of internal ballistics, a slow powder get the bullet moving and once it is moving and the pressure spike is passed the flame reach's the faster powder which can then literally explode behind the low resistance already moving bullet.

Just how I have seen it mentally.

In the war the Germans had cannons with really long barrels that had charges along the barrel in side ports that would ignite as missile passed each port. The start up propellants and the 4 charges down barrel propellants were very different creatures.

[JamesNotBond]

Tree ! I do request that you refrain from these fancy reloads with the rifle I will be using. A plain bang and a hole in the paper is all I need.

Thank You Kindly.

[janfred]

Basically the need for duplex loads have been removed due to better powder.

In SA, the advent of S355 removed any need for duplex loads.

[Ds J]

Basically the need for duplex loads have been removed due to better powder.

In SA, the advent of S355 removed any need for duplex loads.

Modern designs in cases and bullets might have a big influence as well?