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Thread: Duplex loading for 45/70

  1. #21
    Boolit Mold
    Join Date
    Dec 2017
    Quote Originally Posted by Larry Gibson View Post
    From my treatise on my 45-70 trapdoor loads;


    I had several reasons for developing duplex 45-70 loads. Maintaining accuracy w/o cleaning between shots or every 10 shots or so was foremost as I didn’t want to carry a lot of cleaning equipment with me on “walk about” shoots where upwards of 50 shots would/could be taken. I also really detested the use of the blow tube between shots. Increasing the “power” of the loads was not a consideration at all. I wanted simply to lessen the fouling while maintaining original ballistics within the psi range safe for TDs and perhaps improving upon accuracy.

    The smokeless powder charge against the primer aides in ignition alleviating the need for drilling the flash holes and other makes of cases with thicker walls can also be used. The smokeless charge, if sufficient, also “blows out” of the barrel most of the charcoal residue from the BP. This can be seen easily seen by looking from the breach end down the bore after several regular BP rounds have been fired. This residue (BP fouling) builds up and not only destroys accuracy but also can prevent the chambering of a bullet with a tight bore riding nose. The blow tube softens the residue in the leade allowing the bullet to be seated. However, after sufficient rounds fired w/o swabbing or cleaning and chambering, even with the use of the blow tube, will be difficult. [Note; this is why a true M1873 bullet is not a bore rider and the M1882 bullet’s nose is smaller than the bore in diameter sp both will still chamber even after many rounds have been fired] With an efficient smokeless ignition charge there is little charcoal fouling left in the leade and bore so the use of a blow tube to “keep it soft” is no longer needed.

    Additionally with most of the charcoal residue blown out I have found accuracy of a 405 gr bullet that fits the groove diameter and not depending on obturation to fit the bore will not quite but almost as accurate to 800 yards as the M1882 500 gr bullet.

    In developing my own duplex loads I followed Spence’s advice and use IMR 4759 (SR4759) as the smokeless powder in my duplex loads. I had picked up a hundred once fired R-P nickeled cases to use as they would, if useable, allow a quick identification of the duplex load vs a smokeless of straight BP load. Those cases would chamber in my TD so they were close to “fire formed”. I cleaned and NS’d them. I used standard WLP primers and did not drill the flash holes. Actually nothing other than cleaning and inspecting was done to the cases. I started off using 5 shot test strings with 4 gr of 4759 against the primer and (using Spence’s bulk formula of 1 gr 4759 = 2.8 gr FFG) reduced the amount of GC (GOEX Cartridge) by 11gr to 59 gr. Care bust be taken that the seated bullet still compresses the total powder charge. I have not found the compression die to be needed with the 500 gr bullet and probably is not needed with the 405 gr bullet But I use it anyway. I compress the powder so the bullet, at a cartridge AOL of 2.55” for the Lee 405HB, just sets on top of the powder. I use the taper crimp die to just put a slight taper crimp on the case mouth. Additional test loads to, increasing the 4759 1 gr per test while decreasing the GC approximately 2.8 gr per test, 7 gr 4759 and 50 gr GC were loaded.

    Shooting the 5 shots in each test load and inspecting the bore showed that 7 gr of 4759 did indeed “blow out” most all of the charcoal (black streaks) residue and fouling. The barrel was cleaned between test strings. I also found that accuracy steadily increased as the 4759 was increased. Velocity was lower than the 1340 - 1350 fps I was looking for to duplicate M1873 service ballistics. I then kept the smokeless load at 7 gr and began increasing the GC in 1 gr increments. I found that with 7 gr 4759 under 52 gr GC in the fire formed R_P nickeled cases with the 16-1 Lee 405HB the velocity was right at 1340 - 1350 fps, just where it should be to match original ballistics out of the 32 ½” original TD rifle barrel. I have subsequently pressure tested that load (Oehler M43) and found the psi to be 20,300 psi(M43), well within the psi MAP of 28,000 for the TD. The ten shot psi test had an SD of 10 fps and an ES of 30 fps.

    That has been my standard M1873 BP duplex load for use in my H&R Officer’s Model. I have a M1879 “R” Type III (3rd form) rear sight on it and a Beech front sight along with the factory tang sight. With the rear sight set at 100 yards and using the blade of the Beech front sight the POI is just above POA at 100 yards. I generally can hold 10 shots into 2 – 3 moa with the M1879 rear sight (I do better with the tang sight of course). The range regulations have proven quite correct to 1000 yards.

    I next wanted a 45-55 carbine load with the 405HB at 1150 fps out of my H&R LBH Carbine. I took the tang off the LBH (why it was put there is beyond me!) and installed a “C” M1879 Type IV (4th form) rear sight with a blade front sight. I dropped the 4759 charge back to 5 gr (thinking it shouldn’t take as much smokeless to blow the BP residue/fouling out of the shorter 22” carbine barrel proved correct) and loaded 42 gr GC over it. Care must really be used to make sure the bullet does slightly compress the powder. The 405HB had to be seated under 2.55” OAL for some slight compression just as the original 45-55 w/o a wad in it. I left the 4759 charge at 5 gr and increased the GC until 49 gr gave 1138 fps at 15’ with an SD of 6 and an ES of 18. These were loaded with the 405HB cast of 16-1 and sized .4615 and lubed with my beeswax/olive oil lube. I have since switched to the 457124 Lyman cast of the same alloy. It gives almost identical ballistics and is easily identifiable as the 45-55 load by the different bullet.

    These duplex loads have met my every expectation. They are accurate, I do not use a blow tube any longer and I can literally shoot all day w/o losing accuracy from hardened or excessive BP fouling. During a test one time there was 80+ rounds fired from the H&R OM and 100+ from the H&R Carbine in one day w/o cleaning, blowing or anything else. At the end of the test I fired a 5 shot group from each at 100 yards and found they both still were as accurate as if clean. Speaking of cleaning; it is also so much easier w/o all the BP charcoal residue.

    Ok, so what about my original TD target rifle? Well, that was supper easy; I used the same load as for the M1873 405HB bullet and simply substituted the M1882 500 gr bullet cast of 16-1 form the Rapine 460500 mould. Those bullets drop exactly at 500 gr BTW and were sized at 4615 and also lubed with my beeswax/olive oil lube. This time I used standard R-P cases that were fire formed and NK sized. Primers were again WLRs (Other standard and magnum primers have been tested with little or discernable use with these duplex loads). The .4585 expander was used. Both the charges (4759 and 52 gr GC) were thrown with a Lyman 55 and no drop tube used). The compression die was used. Seating was adjusted so the front 1/3 of the driving band was engraved by the leade when the breach block was shut. The taper crimp die is used to just straighten out the case mouth bell. I fired 2 foulers and then 10 shots for record at 200 yards. The group was 2.9”, the velocity was 1200 fps with an SD of 4 and an ES of 14 fps. What could I say except ….sweet!
    Larry: Thanks very much for posting this

    Sent from my XT1585 using Tapatalk

  2. #22
    Boolit Master

    Larry Gibson's Avatar
    Join Date
    Jul 2005
    Lake Havasu City, Arizona
    You're welcome....
    Larry Gibson

    “Deficient observation is merely a form of ignorance and responsible for the many morbid notions and foolish ideas prevailing.”
    ― Nikola Tesla

  3. #23
    Boolit Bub
    Join Date
    Apr 2015
    SW Virginia
    I use the same technique as Larry in my Springfield 1881 trapdoor. 5gr 4759 and enough FFG or CTG to require SLIGHT compression. I do use a compression die. I use the Lyman 457483 and 457125. I use a card wad under the bullet. Also 5744 seems to work as well as 4759. I can shoot all day without cleaning. The technique IS period correct and popular from 1890 to 1920 or so. Everyone just didn't sell all there BP rifles after smokeless came out. Col Whelen was using a 40-72 Winchester long after smokeless rifles were available.

  4. #24
    Boolit Master

    Join Date
    Mar 2005
    Perryville, Ky,USA
    I don't shoot black but had a shooting partner that was nuts over it. Ignition's the thing. He used a very small charge of Red Dot in some, moved up to slower burners like 4759, tried three "strike anywhere" match heads under the black, tried a magnum rifle primer under the black and all shot safely. His biggest concern was powder migration and he carefully carried them base down in a plastic cartridge box. His most interesting experiment was to take a quantity of black and desiccant bags and suck that lot of powder down to 20% humidity by changing and recycling the bags daily. Saturday night, he loaded his ammo and stored it in an ammo can. Sunday he tested it. He was able to attain almost 20% more velocity. An initial burst of white smoke was first out of the barrel followed by a grayer cloud. He wrote it up on the old Shooter's site and if anyone has the archives, they might be able to retrieve his test results. His handle was Petey. He's left the range now and his wife let his journals get away./beagle
    diplomacy is being able to say, "nice doggie" until you find a big rock.....

  5. #25
    Boolit Mold
    Join Date
    Apr 2010
    Reloader 7 is a very good powder for duplexing black. Stick with 10% smokeless to black.

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check