- Location
- Somewhere on the Hudson Bay Coast
With all of the powders we have available there is no need for a North American reloader to use duplex loads. In the RSA however, the reloading powders produced by SomChem do not cover as broad a spectrum, so reloaders there resort to duplex loads, and these duplex loads are commonly published in the local shooting publications.
I saw this very well presented post on AR and thought it would be of interest -
AIU:
This was the scenario:
Somchem produced the following powders
with equivalent ( aaproximated) IMR burnrates:
S 321 = Slower than IMR 3031 and faster than IMR 4198
S 335 = IMR 3031
S 341 = IMR 4320
S 365 = IMR 4350
S 385 = Slower than 4831 but faster than
IMR 7828
In terms of the large bore 450 caliber class we had a problem in that with the slower S341 and S365 would not give us accepted 45 cal 500 gr bullet velocities without running out of case capacities and shooting the faster powders like S335 we could not with max loads attain desired velocities without getting into pressure problems. We needed something inbetween.( that was not made by Somchem )
PMP loaded their factory 458 Win mags with their fast S 321 powder using a 480 gr bullet. This was a very hot load and if you went a full 500 gr using a monometal the pressures were to high. The initial factory spec 458 Win ammo from PMP ran a full 2200 fps, that was very fast and very hot. The charge was later dropped to a more respectable velocity.
Using S321 in the larger 450 Watts case was an option but according to the Powley calculator this was less than optimal. In fact the faster S321 would work in the Watts but with a very low SD bullet. Ie a light bullet.
The Powley calculator shows the optimal powder for the Watts with a 500 gr Bullet to be IMR 4064 which in terms of our South African powder would lie midway between the slower S365 and the faster S335 hence the need to come up with the duplex solution.
If I went with a fast burner I would get to the pressure limits before attaining the desired velocities and if we went slow we ran out of space.
And to boot we ran into pressure problems based on geograpical location. I would load on the highveld and when I took my 450 Watts down to the lowveld would get sticky bolt and extraction with some of the loads.
So what we did was to duplex our loads.
Roughly a 1/3 of the slower S365 at the primer and 2/3 of the faster S335 on top.
As to your question of a duplex load of slow H870 and faster W 760 1:3 one should expect something in the IMR 4831 range.
But we need to know what case caliber, bullet weight etc.
It's not really that difficult or complicated as this is a internal combustion enjin and the rules or mechanics of combsution remains constant.
I saw this very well presented post on AR and thought it would be of interest -
AIU:
This was the scenario:
Somchem produced the following powders
with equivalent ( aaproximated) IMR burnrates:
S 321 = Slower than IMR 3031 and faster than IMR 4198
S 335 = IMR 3031
S 341 = IMR 4320
S 365 = IMR 4350
S 385 = Slower than 4831 but faster than
IMR 7828
In terms of the large bore 450 caliber class we had a problem in that with the slower S341 and S365 would not give us accepted 45 cal 500 gr bullet velocities without running out of case capacities and shooting the faster powders like S335 we could not with max loads attain desired velocities without getting into pressure problems. We needed something inbetween.( that was not made by Somchem )
PMP loaded their factory 458 Win mags with their fast S 321 powder using a 480 gr bullet. This was a very hot load and if you went a full 500 gr using a monometal the pressures were to high. The initial factory spec 458 Win ammo from PMP ran a full 2200 fps, that was very fast and very hot. The charge was later dropped to a more respectable velocity.
Using S321 in the larger 450 Watts case was an option but according to the Powley calculator this was less than optimal. In fact the faster S321 would work in the Watts but with a very low SD bullet. Ie a light bullet.
The Powley calculator shows the optimal powder for the Watts with a 500 gr Bullet to be IMR 4064 which in terms of our South African powder would lie midway between the slower S365 and the faster S335 hence the need to come up with the duplex solution.
If I went with a fast burner I would get to the pressure limits before attaining the desired velocities and if we went slow we ran out of space.
And to boot we ran into pressure problems based on geograpical location. I would load on the highveld and when I took my 450 Watts down to the lowveld would get sticky bolt and extraction with some of the loads.
So what we did was to duplex our loads.
Roughly a 1/3 of the slower S365 at the primer and 2/3 of the faster S335 on top.
As to your question of a duplex load of slow H870 and faster W 760 1:3 one should expect something in the IMR 4831 range.
But we need to know what case caliber, bullet weight etc.
It's not really that difficult or complicated as this is a internal combustion enjin and the rules or mechanics of combsution remains constant.
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