You worry to much.

Your system will become immune to BP smoke. It takes time, like becoming immune to snake venom. Remember to BLOW in the blow tube.

Clean your rifle before you leave the range. 

Gunk in your roller will make it roll better when oil is added.

      Joe.

Ah, but that's the fun of black powder.  Without the belch of smoke, you might as well be shooting a modern rifle.

As for "gunk" getting into the action, you can avoid that by cleaning from the muzzle with the rifle upside down.  Yes, most people will tell you that is an heritical statement.  Fact of the matter is, cleaning from the muzzle will not harm your barrel if you use a proper rod guide in the muzzle.  You are just as likely to ding the muzzle when you clean from the breech and the patched jag leaves the muzzle and the rod "bumps" the bore. 

George

In my 45-120 Shiloh (Bought it for the action but kept it together for the fun) I couldn't get out more than three rounds before the throat was cruded up to the point you couldn't get another cartridge in. So with 7 grains of 4759 and 100 grains of  BP (ideal #6) I can shoot 20 rounds with no issues. The real cheat is to load a couple of smokeless jacketed rounds when done and take a pass on cleaning at all (still a good idea to clean chamber area and throat but it is minimal).

Sometimes duplexing just doesn't work.  For example,  I have a No. 3 Ballard in .25-25 Stevens.  Since this is a cast action, I decided to use only black..or at most duplex loads.  I am using a 100gr. Idea 25720 fixed.  I am using Swiss 3FG.  even using grease cookies, I still had to wipe between shots with barely damp patch for target accuracy..blow-tubing would give 1" groups at 50yds..good  enough for hunting.  I decided to duplex.  I first tried SR4759..didn't make much improvement in bore condition..and still needed to patch bore..though only needed dry patch for match accuracy.  Next I tried IMR PB..this really cleaned things up..bore looked cleaner than any straight smokeless loads..but still needed dry patching thru after each shot.
  I use barely damp patch thru after each shot, groups are around 3/8"..and Butch's Bore shine cleans er' up with 3 patches.  I realalize a .25-25 might be more finicky than a larger bore, but even the .40's only need blow-tubing to maintain accuracy.  And same easy 3 patch clean-up.

The BPCR forum has a section on duplex loading. I would suggest that Jamo post his question over there, but I don't know how thick his skin is.   

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They have that duplex sub-forum for folks to share knowledge and ask questions, but the same characters usually arrive to spoil the threads - and generally drive them over to this forum, anyway....

In broad strokes duplexing was adapted as a way to control fouling. The hotter burn of smokeless serves to consume more of the fouling making it possible to shoot without wiping after each shot or a blow tube. This made Breech seating a more feasible option to the more labor-intensive muzzle-breech loading. 
  The generally accepted rule of thumb is 10% smokeless 90% black. Now is where the fun starts finding a balance between black and smokeless that gives optimum performance in your rifle. 
  You will notice that at the dawn of the smokeless era black was sometimes used as the priming charge. This was because early primers were made to light off black powder a relatively easy thing to do. The new smokeless powders were not as easy to light off properly with the primers of the day. Until better primers came on the market, sometimes a pinch of black powder was used to get things going. 

40 Rod

Quote:


I really don't understand some peoples adversion to duplex loading. It's been around since at least 1890 and duplex was shot in recorded matches of that time period. It's not like it's the "new kid on the block". I really think it's because it would be hard to police in matches. NRA disallow it and they also disallow the Borchardt, one of the oldest of all SS. Go figure......

The only duplex rules that I know of are ASSRA Long Range rules that allow 15% smokeless. Here in the NW we used to have three SS BP matches, one in Springfield, OR, one in Grant Pass (Western States), OR and another in Grants Pass put on by my club (Jefferson State). The Sprinfield club allowed ANY safe duplex load, the Western states allowed 10%, I believe, while I restricted my matches to the 15% rule.

I saw no harm done to any rifle including Barrards and in my case, my model 44, 32/40 Stevens (15%). 

There is no one that can tell you with any certainty that a 10% duplex load will harm your rifle if you use powders as slow or slower burning than 4759. It will just be speculation, as I have never heard of any pressure testing ever being done with duplex loads. 

At least up to 15%, the look, sound are the same, the difference is you don't have to wipe.

All that said, it would be nice to again have BP, ASSRA or ISSA 200 yard matches. Our "Golden Age" time period fits right in with the duplex period, same as the Traditional class of rifles do. 

Frank