A fellow member of these forum requested i fill the powder chamber of the pictured 223 breech plug with 777 powder, finish the load with 80g of BH209, and clock it. He requested large rifle primer be used, and wanted me to compare this duplex load to a full load of BH209. So i did.






This morning, i set a target out at 47 yard, and set the clock at 16 yard. The bullet use in all testing was the 300g Deep Curl in a short black sabot.

The first three shots i took with 85g of BH209, and the clock read

1679 fps
1604
1604

The average of these is 1629 fps, which calculates to a muzzle velocity of 1675 fps.


Then i shot 3 shots using the duplex load, with 5g of 777 and 80g of BH. They clocked at

1515 fps
1563
1555

These average to 1544 fps, which calculates to a muzzle velocity of 1586 fps.





Then i shot 3 85g loads of 777. It wasn't necessary to swab between shots. They clocked

1670 fps
1635
1616

Which averaged to 1640 fps, and calculates to a muzzle velocity of 1686 fps.

Then i shot 3 85g loads of BH again. The first bullet went down hard because it was following 3 777 loads, but i managed to seat the bullet without a lot of pain. They clocked

1638 fps
1685
1598

Which averaged to 1640 fps, which was exactly what the 777 was, and of course the same 1686 fps muzzle velocity.





It seemed to me there was a large spread in the velocities. I figured it was my doing, because i wasn't being consistent enough in my measuring using the TC U view measure. I tried as hard as i could, to be consistent. To check and see if this was true, i shot 3 shots of 110g BH that had been measured by the Redding 3BR powder measure. These shots clocked at

1787 fps
1796
1796

These 3 speeds average to 1793 fps, which calculates to 1843 fps at the muzzle.




After shooting all these shots, only 2 groups are still visible on the target. The top 3 were made by the 85g 777 load; the next 3 down were made by the duplex load.

Great report Ron, and well done on the testing procedure. I'm impressed at how close the BH velocities were in the two pure BH groups, except for that first shot (1679 fps). Do you think that was because of a cold clean barrel?

Nice test. The duplex would definitely aid in very cold weather hunting since T7 is easier to ignite. Western Powders gave me the thumbs up to try but I never got around to it. I was advised its just like using Pyrodex pellets with the igniter on one end.

The barrel was indeed, clean and cold.

The data that impressed me was the very last shots on a hot dirty barrel--the 110g BH shots. Uniformity like that isn't regularly seen with center fire rifles using weighed charges. It seems that using a powder drop works just fine for measuring BH209.

To me, providing a small volume of BH for the primer fire to first encounter, which is done when using a breech plug with a chamber on the end, is like having a duplex load without having a second powder.

It seems this smaller volume of powder inside the chamber is easier to ignite than the full volume, and it then ignites the rest of the powder column. My mental picture of what happens when a powder chamber is provided may or may not be correct, but it does fit the data. Breech plugs with powder chambers, have ignited BH reliably whenever i have used them in the worst of conditions. This includes sub-zero temperatures, small flash holes, carboned flame channels, excess head space, and loosely fitting sabot.

Ron,
I agree with you about the powder chamber but for those not using modified plugs with a powder chamber could benefit from the 5 grains of T7 under the BH209 I believe. If you took a stock CVA plug in your Accura I bet it would be hard to make it misfire with a little T7 poured in first.

Makes sense. Do you have an idea why the duplex load had such a drop in velocity compared to the non-duplex load?

My guess is the "booster" of only 5gr might not be enough to gain any fps. Some T7 is likely sticking in the barrel and mixing with the BH209 too much. The idea behind a duplex is to raise pressures enough that the main charge reaches its required pressure curve quicker. T7 does spike pressures faster and BH209 has a broader/longer curve without being higher than straight T7. The noticeably lower fps is still a bit odd though.

Maybe a 10gr booster and 75gr BH209 would provide some insight. Trying the same experiment with a 209 primer breach plug might also or maybe with a 250gr bullet to see if it continues to produce less fps.

I like GM54-120's idea. I would also like to see what a 209 primer does since it is hotter.

I wonder if an ignition charge of real black powder would make a difference. It's may provide a quicker ignition boost.