duplex loads???

Retrieved: 12/20/2014
Last Post: 03/25/2007

I heard a fellow talking about his duplex loads in his 45-70. What are they?

Hedley Lamarr
March 20, 2007

A duplex load is common terminology for a round loaded with 90 to 95 percent black powder, with a 5 to 10 percent volume of smokeless powder placed at the bottom of the case prior to the black powder.

The idea being that the smokeless will ignite first and provide a much hotter flame for igniting the large volume (in a long skinny tube) of black powder.

It also makes less fouling.

It works too.

Just remember, duplex loads are not allowed in SASS competitions, and I would be adverse to using them in any antique firearms due to the increased pressure.

Ed Malinowski
March 21, 2007

You can also duplex with 4 Fg black powder under the 2 Fg black powder. Not having reviewed the SASS rules for this, I do not know if it is legal or not for a SASS match.

Grapeshot
March 21, 2007

Yep, a small charge of smokeless under a large charge of Black Powder or a small charge of 4 Fg under a large charge of black powder is what they are talking about.

When I was shooting N/SSA I used to stick about 15 grains of 4 Fg under the main charge of my Sharps paper cartridge. I was using Pyrodex and needed something that was heat sensitive and would ignite fast to set of all that Pyrodex under that .50 caliber bullet.

John Boy
March 21, 2007

Might add - a slow burn rate smokeless powder is the best: ie 5 gr 4198 to 60 gr FF or FFFg, which will yield the 7% that Ed recommends.

Dick Dastardly
March 21, 2007

I'm probly the one that spoke out of school... Yes, I do shoot duplex loads and yes I do benefit from them. However, be careful with this idea. You can't just go willy-nilly putting any ol' heathen fad smokeyless powder under Holy Black and expect to be safe. I found my load information in an old Lyman manual. I studied it well and then worked up loads very carefully. My final load is as follows.

45-70 *-* brass fired at least once in my Rem roller and not resized.

CCI 300 Large pistol primers

.5cc SR-4759 powder

64 grains FFFg standard grade Holy Black by volume.

1/16" .460" Circle Fly over powder wad. Compress enough that...

DD-45-70-500 Spire Point bullet, lube/sized to .458 will seat with thumb pressure only till the top lube grove is just above the brass.

When I chamber the round the rifling just engraves the first driving band of the bullet. The burn is very clean.

Lars
March 22, 2007

The few uses of duplex loads I have personally been around all gave so little powder fouling that bullet and lube (if any) choice was pretty much open to any bullets that happen to give suitable groups in your rifle, including metal and paper jacketed bullets.

Concur with the comments about using nitro + BP duplex loads ONLY in suitably strong rifles, preferrably of modern steels, in excellent condition. Such as Winchester High Walls, RBs with receiver blocks specially heat treated for higher pressures for use with modern (1880s and later, such as 8X58RD) rifle cartridges, Winchester 86s, Marlin 1895s, Ruger #1s, etc.

Dick Dastardly
March 22, 2007

I worry about posting about duplex loads.

I would caution pards that want to try these loads to do a LOT of research first. If you do give them a go, start off very conservative. If you can get someone that has a pressure test lab to get you a reading on your loads, do it. If you can find a pard with a lot of experience at long range black powder cartridge shooting, pick his brain. There is much to learn and it's not all conveniently written down.

Yes, duplex loads do have benefits. Also yes, they have dangers. The load I posted was found in a reliable loading manual. I deliberately went to the conservative side. This season I'll get a lot of experience with it and I will report back. Please know that what works good in one gun may be poison in another. Also know, when you pull that trigger on an unknown load, there's a LOT of violence goin' on right next to your face. If things go sour, you'll be the first one to know, or not.

Take care, be safe, enjoy the sport.

Lars
March 25, 2007

Anyone out there have any crusher pressure data for the old duplex loads listed in late 1800s data sources?

All the old load data I have seen had almost as much BP as in nonduplex loads. With the much more complete burning of the BPs, caused by the small amount of nitro powder, how much did/does the chamber pressure actually increase.