There had been question once on if I had ever worked duplex loads in my cartridge rifle. Going through my very old reloading books I found this handwritten load on my 45-70 trapdoor page. I will say again I do not think these worth the effort but for those who wish to experiment here is the one load I have found so far. As it includes Pyrodex RS my assumption after all this time is that I was trying to get more efficent burn.
 
THIS DEFINATELY FOR SINGLE SHOT RIFLES ONLY
 
Federal 210 Primer
340 Grain flat nose hand cast lead bullet.
5-10 Grains Unigue for igniter
Fill case with Pyrodex RS till light compression with bullet seated.
Very little or no crimp, you want the bullet to hold the compression on the powder and not shake out in normal carry in pouch or pocket. This will be between 52-56 grains Pyrodex RS.
 
Effectively this creates a hot primer. Start at 5 grains and work up. Stop when your groups fall apart.
 
I was playing with this idea some twenty plus years ago and do not now use these loadings now. Finding using black powder in 2F or smokeless loaded down to Trap Door pressure levels completely satisfactory for the game I hunt. Mainly Whitetail deer and hog with this weapon.

I'll have to try that one out Alboy. What do you think it'd do with that 535gr. bullet?

Well if you have a working load in pyrodex or some black powder I would reduce around 20% and work it up. I know you have pretty strong action. My experience with BP loads is that you have to make a 10% percent change to get noticeable change in performance. I also think you can get the same or better performance out of simple BP loads with going to magnum primers if you need the help lighting off large cases of powder.

I thought I might throw my own 2 cents in since I have a lot of experience with BPCR, and duplex loads.

 
The best part (if such can be said) in using "duplex" loads is the lack of fouling in the bore. The standard recommended "duplex' load is 6grs. SR4759, and a "packed" case of Goex FFg, which will amount to about 62gr. of FFg.

 
Lyman recommends to NEVER use more than 10% of the black powder load with your duplexing. Of course many rifle manufacturers recommend you NEVER use duplex loads of any kind....we live in a day of liability awareness!

 
Duplexing goes back to the days of Harry Pope, the Creedmore matches, and of course long before that great thing called smokeless powder was invented.
Even "duplexing" Fg, with FFFg was considered a foolish trick with the barrel steels of yesteryear...but the lawyers were not quite so greedy in those days.

 
Several powders have been used for the duplexing of real black powder, with Unique, RL7, and SR 4759 being some of the prefered.
We all know that in "todays cases" we can never stuff 70 grains of black powder in the case, and still have room to properly seat a bullet.
Even using a 30" drop tube, and very slowly, and very methodically tapping the case, I have managed to only get as much as 68gr.

 
I have come up with a device that I had all intentions of getting a patient on, several years ago before I lost interest It was the use of a wooden loading block, set on an electric razor, and the filled cases were vibrated for 20+ seconds, than an additional 8/10 grains of FFg could be added by using a Lee Dipper....neat huh?
 
 
In the old days, with balloon head cases, getting 70 grains in the case was possible, but in todays world the 45-70 should more aptly be called the 45-60, as that is about what most shooters are using.

 
When shooting the 535gr Postell, with a .030 card wad, and a compression of about .125 you will be lucky to get more than 53/54 grains of FFg in the case.
And, as a side note...Goex powders do seem to perform better with compression, how much compression depends on each individual gun. At one time I owned a C.Sharps that "needed" at least .200...and thats a bunch! While an H&R Buffalo Classic only wants a "light" .010....go figure!

 
When using a duplex load you do NOT have to wipe after each shot, or use a blow tube for that matter. You can shoot a match..... 20 sighters, and 40 shots for record, w/o cleaning, or wiping. But, if you're not using duplex loads, you will never get more than about three shots without accuracy going south on you.

 
Duplexing will increase velocity by as much as 200fps, and here is where we need to be careful....That velocity increase comes about because we have a more "complete" burning of the black powder, and with "complete" burning we have a pressure increase. and because we used smokless we have a "pressure spike" to get that increase...see the picture? Nothing is free!

 
Duplexing with smokeless, and real black, should NOT be use in Trapdoor Rifles, or for those looking for Trapdoor velocities.
 
Smokeless powder used for duplexing must always be loaded first, directly over the primer. A Fed 215 Magnum primer is NOT necessay when using duplex, and some accuracy nuts advise against it.
However, When using pure black straight, or any of the faux powders, the Fed 215 primer is always recommended as it was originally designed for the Weatherby Cartridges with their "taller than normal" powder column for the time. To the best of my knowledge, the Fed.215 primer, is still the hottest primer we have available.

 
I have never duplexed with ANY of the faux powders. I don't know of anyone who does. That business might get even toucher...I have no clue.

 
I hope this helps somebody. Loading duplex loads should NOT be taken lightly, and I recommend further reading from the folks like Lyman. Just keep in mind that Lyman's bottom feeding lawyers, are not going to let Lyman hurt us...if technology will prevent it. And, some of the stuff one reads on the Internet will get up the creek without a paddle....quick!
 
 
I also hope Alboy doesn't mind me steppin in here, but I do have considerable experience with the uses of black powder.

My experience parallels RumRunner's.  My duplex loading settled on SR-4759 and has not changed in many years.  But, as RR indicates, any shooter is on his or her own when it comes to 'duplexing'.

Like RR, I've never messed with 'substitue' black powders and have no knowledge of their properties.  

Action strength must always be addressed and if you do not know, you must ask someone with the requisite experience.

Rum Runner
 
Rather than worry if you are stepping on my toes let me thank you for getting in here. What little duplex I have done and the load I posted was many years ago and I quit the experiment as not productive to what I needed out of coal burners.
 
The only reason I addressed this situation is because of people asking about the possibilities and I feel it better to give some starting points that did not do me harm and give warnings to proceed very carefully.
 
I have come to the frame of mind that if you want something like 458 Nitro Express performance then go buy a 458 Nitro Express.

"Rather than worry if you are stepping on my toes let me thank you for getting in here. What little duplex I have done and the load I posted was many years ago and I quit the experiment as not productive to what I needed out of coal burners".
 
 
 
Thanks Alboy. Just before I finished the post I started to think about "forum etiquette", and almost deleted my post...but then I thought "someone may find it helpful", Alboy may not mind, or might even be looking for a little help???...so I kept pecking away.
 
Sometime when I head down Midland / Odessa way, I'll have to look you up...buy you a cup of Joe, and talk a little blackpowder shotgunning.
 
When I lived in that neck of the woods, I was considered less than normal, and probably looked down on, by even suggesting we shoot black powder while quail hunting. 40 years later, those same hi-flutin fellers are asking for advise about their front loaders....go figure!
I'm very tempeted to tell some of them "they should have paid attention years ago", but I guess that's not in me.
 
Kinda funny how we go through different "stages" of life. I was no different, muzzleloading was off, then back on, for years. But I can't say I ever lost complete contact with it...I always had two / three / sometimes four of 'em around somewhere. Now I have a safe full of smokeless powder guns that the kids and grandkids can argue about when I'm gone.

Washington state. Yea I guess after traveling that far another 600-800 miles won't matter. If yo get that far lets talk and I'll try to split the distance with you some how.
 
On occasion I go to Calgary for the people that give me checks, I don't do any thing to earn them but they give them out any way. Next time out I will see if there is a mutual meeting place that might work to get that coffee and then I'll spring for the steak.
 
I do not claim expert status on any subject except how to get My Love to bean me with the nearest heavy object. On that I am a past master and she is an extremely tolerant young lady. That said I do not take umbridge at being corrected or informed. The day I know it all about anything is the day I change direction, nothing left to learn makes for a dull day.