Front ignition / Duplex loading.

Retrieved: 08/27/2016
Last Post: 03/17/2010

I heard or read about this some time ago and thought it was quite interesting.

Have any of you experimented with this type of loading?

Apparently Duplex loading can also be thought of as mixing powders to have a fast powder at the base for initial burn and a slower one for the remainder of the charge, which is just asking for trouble and is not what this post is intended to discuss.

The following is a brief description I found on the net.

The most famous of those fooling with front ignition were Charles O'Neil, Elmer Keith and Don Hopkins. Every gunny knows of Elmer Keith.

This was called duplex loading. In addition to a tube threaded into the primer flash hole to carry the flame up near the front of the powder charge this method of loading also used a smaller charge of faster burning powder at the casehead. It is very interesting, though. In our world of fast food and microwave meals I seriously doubt that very many will bother with this technique today. It is easier just to get a gigantic case and use gobs of extremely slow burning powder.

Still, the idea of front ignition duplex loads is intriguing. The claim for these loads is higher velocity, longer barrel life and reduced recoil.

The higher velocity claim is true, the things against this are fairly simple. One, these loads look like a pain in the patootie. First we must go through the hassel of threading these little tubes and the cases, then inserting the tubes. We must then modify our sizing dies for handloading these cartridges. Then we have to find the right sized drill rod and temper it for decapping the fired cases. Then we have to figure out a way to keep that fast burning powder from getting into that flash tube.

Still, it's interesting. The idea that barrel life is longer comes from the lack of "sandblast effect" of the unburned and burning powder granules hitting the barrel. Lighting the fire from the top means the burning powder gasses force the rest of the powder to stay down, at the same time forcing the bullet to go up. This is only logical, just as the conventional priming would have the gasses start at the bottom and force everything up.

This is where that faster powder comes in. The slow powder has already been burning, the gasses have already been pushing the bullet a bit down the bore. This, in effect, makes for a great big "case". Like the old black powder cases used with modern powders, that big combustion chamber means we need a fast powder to make lots of powder gasses, quick. So, in duplex loading we have this fast powder to give another boost in gasses just as the pressure is going down.

This means, when it works right, a longer peak pressure curve. So we get higher velocities. The lower recoil for the same velocity is also simple, in conventional cartridges the way to increase velocity is to make the case larger and use larger amounts of slower powder. Since heavier weights of powder increase recoil (for every action there is an equal and opposite action) the front ignition duplex loads really work.

Trouble is, this is a mid-Twentieth Century idea in the 21st Century. Even then few were interested in the idea. Conventional handloading of ammunition is actually pretty simple. Recipes for loads abound. Anyone willing to follow directions can load safe effective ammunition. There are few such recipes for the front ignition duplex loads and it seems we are at the end of an era for that kind of experimentation. What a shame.

jimkim
March 17, 2010

Veral Smith did some work with regular duplex loads. If memory serves, he used a fast powder(at the bottom) as a kicker and 20mm cannon powder for the main charge.

darkgael
March 17, 2010

I really would like a link to that article. I don't doubt your post but the info doesn't sound right to me, especially given the progressive nature of smokeless powders. It sounds too simple.

I have constructed cartridges with front ignition tubes. I have duplexed loads. I have not done them together.

"a pain in the patootie"

Absolutely.

Front ignition is an interesting idea but it poses a number of real problems for the handloader. First, the cases with tubes are labor intense to make - no sophisticated skills involved just a lot of small work per case. Loading is a tad more complex because you now have a tube that must stay clear right in the way of where you are going to drop powder. After firing, depriming the case is complicated by the presence of the tube, which sits in the primer hole.

Most duplexing that I have read about has involved black powder in large cases. I constructed my cases for black powder loads using the large 577-450 Martini-Henry case.

There was a reduction in extreme spread in the loads that I tested. The change was hardly worth the trouble.

Lyman used to include data for duplex loads in its "Cast Bullet Handbook". All the cartridges involved were large volume BP numbers from the 45-70 to the 50- 140 Sharps. The smokeless kicker in each case was SR 4759 (basically the smokeless charge was about 10% or less of the total charge weight).

Paul Matthews did work with duplex loads in the 45-70; he also used SR 4759.

BTW - Duplexing black powder with Pyrodex is a way to use the substitute in a flintlock (other subs too).

The problem that I see with duplexing two smokeless propellants in a case using front ignition is timing that bit that was cited about "another boost in gasses just as the pressure is going down."

How does one know where in the pressure curve the boost is going to occur? And how much of a boost one is going to get? If the fast powder is dropped first and the main, slower charge on top of it, then the length of the ignition tube is a factor as the spark, rather than propagating through the entire charge, is going to be localized at the front of the main charge (so it would seem). Just how far forward the tube carries the spark will influence how the main charge fires and thus when it gets to the faster "boost" charge.

That all sounds a bit sophisticated for handloading.

Need that article.

Pete

That's why I'd like to read the article if a link can be provided.

Slamfire
March 17, 2010

I really don't think gunpowder in a case burns like a candle.

On the face of this, the idea just sounds great. Pour powder in like a layer cake, just the layers have a different burn rate.

But I would like to see some actual pressure curve data before I tried something like this. Might be some very unpredictable spikes.

Now I understand there are layer cake rocket motors. The propellant is cast in these motors, the stuff is solid, not loose like gunpowder.

Brian Pfleuger
March 17, 2010

Maybe I'm a little naive about the engineering challenges but it seems to me that if front ignition really offered significant advantages then it would be no big deal to develop a case and primer system with the primer seated in the forward part of the case.

Sure, it would require new depriming tools, new firing pin configuration and new case and primer designs but the accuracy freaks will spare no expense.

Scorch
March 17, 2010

If you read the O'Neill/Keith/Hopkins material, you will also note that Elmer Keith said that while it worked, it was not practical. So basically yes, there is some benefit, and no, we aren't going to make you any ammo. I am beyond playing around with extended flash tubes and duplex loads. At one time I might have, but it has been tried by some guys with a lot more money and knowledge than me and dropped, so I took a hint from that.

Quote:
if front ignition really offered significant advantages then it would be no big deal to develop a case and primer system with the primer seated in the forward part of the case

The Dreyse "needle gun" used just such an ignition system back in the 1830s (black powder in paper cartridges). It was abandoned as impractical due to frequent firing pin breakage and other issues.

Brian Pfleuger
March 17, 2010

I meant on the OUTSIDE forward part of the case though. The head area would be solid. The primer would have to be a curved shape to match the case. Yes, I know that there would be issues with different curve angles. Essentially the firing pin could be little different than a hammer on a typical revolver.

brewman
March 17, 2010

Personally I would not fool around with mixing smokeless powders and I was purely interested in the principle of front ignition using a single powder and wondered if anyone on this forum had tried it as it seems to have some merit even without the secondary powder boost.

darkgael,
I am sorry mate I do not have the link, I found the info by just doing searches using some of the keywords, if you do the same I'm sure you could find it or similar info.

Crosshair
March 17, 2010

I tried the "layering" method awhile back. Didn't see any advantages and it was a lot more work. Didn't blow up any guns.

zippy13
March 17, 2010

During my service days, I recall seeing naval artillery shell cases with extended flash tubes. Don't know if they had a laminated powder charge, but it would be a lot easier to accomplish at the larger scale.