To get consistent results with duplex/triplex loads you MUST load at 100% load density or above (compressed), otherwise as the cartridges are carried around the powder charges will mix together and you'll lose the advantage that you're trying to achieve and your pressure results will be erratic. If you're duplexing up on the top-end of the pressure scale, can you say BOOM?
Me? I don't. I do know a few older guys that were around back when that was acceptable wildcatting practice though.
Originally Posted by reynolds357
I have never heard of fast being used under slow except for Elmer Keith using fast behind slow on the OKH cartridges that had the front ignition tubes. In essence, in that case fast behind slow is the same as fast on top of slow in a normal case. That is interesting. Maybe hubel will weigh in on this one.
What Hubel is doing with that 12FH is using the BlueDot as a starter for slow burning rifle powder. Some blackpowder cartridge shooters are doing the same thing with the large BP cartridges. Using a small charge of a fast-burner to ignite a big main charge.
With the 12FH We're talking like a .75 caliber cartridge here though too...darn near a small field artillery piece!
It's the same concept as using a fast ignitor charge in the loose-bag naval guns (16" US, 38cm SK C/34, etc) The British 13.5" and 15" navals used a similar fast starter charge except as part of the initial cordite charge bag.
There's lots of info on hubel458's 12FH ongoing saga in this thread. He doesn't pop in to often except to update that thread. You don't see him around the rest of the board much either. It's an interesting read.
I know a couple guys here that futzed around with some of the Gibbs front-ignition wildcats (similar system as the OKH front-ignition setup). They pretty much settled on not bothering with the front-ignition and just formed their cases as traditional rear-ignition cases instead.
Back then, with very few powder choices to pick from some guys tried all sorts of interesting (dangerous) things to squeeze more fps out of a cartridge. With the advent of better pressure measuring and other load development methods, it is generally wiser to find a larger case and stick with acceptable pressure levels rather than super-stoking the case you've got to dangerous pressure levels. There's always a bigger parent case available if you want to go faster.
Both the front-ignition and the duplex/triplex loads are pretty much unnecessary for standard-capacity cartridges with the burn-rate range and number of powder choices that we've got available these days.
Personally, I tend to think more on the lines of efficiency rather than raw fps for my reloading. After burning out a few barrels shooting prairie dogs and coyotes I've decided that backloading just a hair will make things last a lot longer and still get the job done to make the fur fly.
How much fps can I get for a given powder charge and how much more powder (and pressure and barrel wear) is it going to cost me.