Duplex 45-70 loads

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Glenn R. Latham posted this 05 July 2021

I tried some duplex loads for the first time in my original Trapdoor, and I was pleased with the results.  Shooting was plinking at steel plates on the hillside, unknown size & range, but hits were often enough to be interesting.  Accuracy seemed to hold up without wiping or using a blow tube (which I don't have and don't really want to get into).  This was at the NRA Whittington Center, where the air is VERY DRY!

I used a load I got from one of Larry Gibson's old posts of 7 grs. of 5744 and 52 grs. of Elephant 2f.  I compressed the load as necessary to seat the Lee 504 gr. bullet cast of 20-1, and used a .060 LDPE wad under the bullet.  Lube was Emmert's with lanolin added.  My question is all I have now is Goex 3f, and I was wondering if that would be safe to use in the same duplex load?

Glenn

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delmarskid posted this 05 July 2021

I would cut back to 5.g of 5744 to start myself. Duplex loads can run up pressures a bit over regular black and FFF maybe more so. I like duplexing. I've done 50 rounds without tending the bore or chamber throat many times. the cases even stay cleaner. I'm using 7.g of R7 520g bullets 62g of 2F or 1.5F with a card and a .10" of compression. My rifle is a High Wall copy so I get away with it. They might hatch your trapdoor. 

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Larry Gibson posted this 05 July 2021

I've been using, and have thoroughly pressure tested, the use of 7 gr 4759 under 52 gr of Goex Cartridge, FFg and FFFg using both the Lee 459-405-HB (410 gr bullets +/-) and the Rapine 460500 (500 gr bullets).  It is my standard load with either bullet using any of those powders.  Velocities stay consistent at 1350 fps +/- and 1250 fps +/- when replicating the M1873 or m1882 ammunition.

The SAMMI MAP for the 45/70 Government cartridge out of deference to the M1873 Springfield Rifle is 28,000 psi [transducer or strain gauge] .  The 7 gr/52 gr BP load runs close to the same or about 1,000 psi higher than the psi of the same powder loaded at straight 70 gr.  The measured psi runs from 17,000 to 23,000 psi [depending on bullet and granulation of the BP] with any of those Goex powders. 

The highest measured psi I've recorded with BP in the 45/70 Government cartridge with straight 70 gr load or 7 gr 4759 under 54 gr (2 gr more than the OP is using of BP) was with some original Dupont FFFg "Superfine".  It has the granulation of current Goex FFFFg BP.  the measured psi ran 24,600 psi with a straight 70 gr load and 25,000 psi with the duplex 7/54 gr gr 5759/Superfine load.  Both still well under the SAAMI MAP for the cartridge for use in the M1873 Springfield Rifle.

During the same testing session I pressure/velocity tested some original factory loaded REM-UMC 45-70 Govt cartridges.  They had swaged 405 gr bullets (lube grooves were quite shallow and were canalure rolled into the bullets.  The 70 gr powder charge was heavily compressed and the granulation was close to that of Goex 4f and 3f.  The measured psi was 22,000 psi and the velocity was 1233 fps which is at the top end of any measured psi's of the duplex load [7/52 gr].

The idea of using these kinds BP loads is well explained in Spence Wolf's book.  The main purpose is to blow the fouling out of the barrel [the OP has discovered the recommended duplex load does indeed reduce the BP fouling left in the barre thereby negating the need for "wiping" or the use of a "blow tube" and accuracy is maintained over many more rounds .....the use of this type of duplex load is not to increase the velocity or pressure over straight BP loads.  This type of "duplexing" reduces the amount of PB used an appropriate amount for the smokeless powder used thereby maintaining the intended velocity and pressure.  It does indeed accomplish that.

LMG

 

Concealment is not cover.........

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Eutectic posted this 06 July 2021

I was going to comment about my duplex loads in my 71-84 11mm Mauser which was a "43-70". However Larry covered all the bases. Duplex loads allowed an afternoon shooting with no cleaning which was great. The loads still made the nice white cloud and BP smell.

Steve

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Glenn R. Latham posted this 06 July 2021

Thanks Larry, that sets my mind at ease.  This rifle is in really nice condition and I'd like to keep it that way!

Glenn

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