Duplex Loads

I wanted to start a new page dedicated to Duplex Loads. At first I will post some internal links to contributors that have mastered them like John Kort and Shasta.

• Shasta and John Kort - Reloder 7 Duplex Loads

From the same information/conversation between Shasta and John Kort, ...Carlson Highway posted some recent information using IMR-4227 and H-4198 (Leverguns forum). 

Sat Aug 29, 2020 6:09 pm

I make a similar load in .44-40:

I talked to John Kort a good deal about duplex loads before he passed away and this is what I developed here in discussion with him:

Firstly, duplex loads with black powder and a smokeless priming are time-honoured load and were used a good deal by target shooters in the early years of smokeless powder production. (Duplex loads combining different smokeless powders are a quite different animal and are not what is being discussed here).  

I ended up with a load which was an unsized case, loaded with 6 grains of 4227 underneath 30 grains of 3F Scheutzen. This was compressed by 0.2 of an inch. This is now a solid cake of powder, and the smokeless "priming" cannot migrate anywhere.

With pure lead bullets with 1-2% tin seated on top and lightly crimped just to hold them this load was the most accurate .44-40 load I have with two different rifles (Uberti 73 and a Rossi 92) Both rifles would shoot 5 shots into 1.5 inches with their open sights at 100 metres. I would often shoot the first three shots into an inch.

The bullet was John Korts version of the standard bullet but with a larger lube groove, the lube I used was mostly lard with a bit of beeswax in it and very soft.

I never could get a full black powder load to shoot better than about 3 inch groups at the same range with either rifle. It must be a lube thing but I never solved it.

Sun Aug 30, 2020 8:23 am

I really couldn't say, I was under the impression that the smokeless priming cleaned up the bore for the next bullet, so acted as if the bullet had a better lube, but I am not sure of the mechanics of it, you could be correct. I am standing on the shoulders of the target shooters of the period, who used loads like these up until the 1920's.

It made no real difference to velocity compared with BP loads of between 36 - 40 grains, slightly slower in fact.

Out of interest, I recall the amount of H4227 was quite specific, as 4 grain or 8 grains resulted in terrible accuracy.

I tried other things trying to get a better full black powder load that was accurate, I tried different cardboards wads or discs of card, grease cookie attempts, and I tried a bit of newsprint over the primer to make a lighter one (the old BP primers were weaker than now) different compression so f powder and amounts, up to the proper 40 grains. Never could get a load anywhere near as good as the BP with H4227 priming.