Home Forums Hunting & Shooting BPCR Duplex loads

Okay, here's a question that might bring a lot of growls and groans. What are your opinions and uses of dulplex loadings? I've looked back through several months of discussions and have not found this subject. Also, I'm asking about all kinds of duplex loadings, those that use a small amount of smokeless powder as well as those that use a little FFFFg within the regular charge of heavier grained black powder.

Mike - I'm not going to "growl or groan" about duplex loads as I have never personally tried them. I have never had a reason to even "duplex" with different granulations of BP in the same load. I have only been shooting BPCR weapons for about 15 years and have had satisfactory results using just BP under my bullet of choice (but I don't shoot "sanctioned" events so I'm easily satisfied ). If you have any inclination to shoot at a sanctioned event, I don't believe duplex loads (smokeless/BP duplex) are allowed although the rules may have changed. I have had zero misfires or "duds" to this date using just BP - I figger why try to fix something that ain't broke. If it is just curiosity you need to satisfy, give it a try. If it is because you want to get velocities higher, get an 06 . . . the bigger (500 gr+) bullets shoot better at the "std" BP velocities and they definitely are more than adequate for anything I have killed, including paper.

Shoot straight . . .

I have and do use duplex loads consisting of the least amount of smokeless under black that I can get by with. I want to qualify that a bit. The only time I have to use a duplex load is in an old double rifle that I simply couldn't achieve the necessary velocity for the barrels to regulate when using straight black. Adding only 5 grs. of SR4759 to my black load put the old rifle on the money. It was a last resort. I have played with duplex loads in other rifles and they do shoot exceedingly clean but I do not use them as a matter of course.

There's really not much need for duplexing smokeless and black. That was done in the early days of smokeless as blackpowder primers wouldn't reliably ignite smokeless, so they drop a bit of black under the smokeless.
Not exactly sure what brought about the smokeless under black loads, but one needs to be a bit cautious about those as they do raise pressure's and, using any compression with that could possibly be disasterous. If a person needs clean burning there's always just plain ol smokeless, altho that can proove a bit dicey as we were so horrifically reminded of when an old ballard blew on the firing line at the Quigley this past weekend.
Duplexing black , might be helpful if you have some junk powder and are shooting big cases, but other than that, just buying good black powder and knowing how to load it will probably be much simpler and just as affetive.

Hmm..Kynoch and Birmingham Proof house disagree that duplex loads increase pressures. In one example, straight from their records of pressure tested loads, in the 500 BPE the original load of 136 grs. of straight black under a 340 gr. bullet the pressure was 10 tpsi. A duplex load of 15 grs. of SR 4759 under 110 grs. of GOEX Ffg gave 8 tpsi under a 440 gr. bullet. The same was seen in the 450 X 3 1/4 BPE with several loads, less pressure with duplex loads than with straight black loads. Oddly, the 500 BPE duplex load was less than 10% and the 450 X 3 1/4 load was closer to 15%.

I can see no really good reason for duplexing in a single barreled rifle, unless as Ranch said one has less than quality powder, a big case and a need to control fouling other than wiping. In a double rifle such is often not the case. Rarely, very rarely, is enough velocity achieved to bring the barrles into regulation with a straight black powder load. After working with over a half dozen doubles chambered in BPE cartridges I have never achieved it. As with all things reloading one must pay attention to what they are about when utilizing duplex loads. I'm convinced they're entirely safe if loaded correctly. Kynoch and Birmingham Proof House were definitive for me.

"As with all things reloading one must pay attention to what they are about when utilizing duplex loads. I'm convinced they're entirely safe if loaded correctly."

I agree. One must consider what they are trying to accomplish, and whether duplexing or any other approach is optimal for the purpose.

In my case I found that about 4.5 grs. of RL7 under a full charge of Swiss 1.5 gave my .45-90 a velocity boost of 75 - 100 fps over an equivalent volume of straight black, to about 1325 fps, with excellent accuracy for long range gong shooting. It did not take a lot of work to arrive at this combo; I guess I was just lucky, but I saw no reason to experiment any further. Note that this involved a very small amount of smokeless, about 5.5% of the total charge weight. Note also that it did not eliminate fouling, or the need to wipe or use a blow tube between shots. That wasn't my goal anyhow.

All of that said, I don't believe in pushing a BPCR or any other firearm to its absolute limits. I think that's asking for trouble.

YMMV, as the saying goes.

Paul

Interesting stuff, never have tried them. My old Rodda Field's Patent single shot came with fixed sights - which I did not wish to alter. It took a while to find loads that would shoot to the sights, and they weren't light loads. If I stumble upon another one like it, duplex might be interesting.

Isn't some compression of the duplex charge required, to keep the two powders from shaking around, and mixing?

Tex, a load w/BP in it MUST be in physical contact with the projectile.

If you're loading the smokeless on the bottom and then filling the rest of the available case space with black. And going by the intructions to make sure the bullet is in firm contact with the powder, How would the powder shake around and mix?
No pressure gains is always a nice theory, but folks there's seldom if ever anyway there's a velocity gain without a spike in pressures...

Thanks, I should have phrased the question better. What prompted it was trying to understand this comment, since I gather that proper compression is important to BP:



What difference is desired/appropriate between firm contact and compression?

Firm contact means the bullet is solidly on the powder, Compression means you have to mash the powder into the case to get it to fit.
Compression with blackpowder is generally considered good. Some smokeless powder when compressed gets damned dangerous.

I expect Kynoch and Birmingham Proof House know what they're doing. Birmingham Proof House has been at it since 1868. Those figures were taken from loads proofed in 1997 or 1998 so it isn't as if it's century old data. Duplex loads tested in the 450 X 3 1/4 were as follows.

Straight black
120 grs. straight black
365 gr. bullet
1750 fps
12.0 tons pressure

20 grs. SR4759 under 60 grs. GOEX
320 gr. bullet, cast-gas check
3, 1/8 in. cork wads
1822 fps
6.7 tpsi

20 grs. SR4759 under 60 grs. GOEX
360 gr. bullet, cast, gas check
3, 1/8 cork wads
1700 fps
7.14 tpsi

Same charge
350 gr. Hornady soft point
3, 1/8 cork wads
1648 fps.
8.05 tpsi

All well under proof and original load pressure, even with cork wads, with "close enough" velocities for regulation except for possibly the jacketed bullet from Hornady.

Curious isn't it.... For all the prickin around and escaping sepearated cases with all those cork wads, the best they could come up with was a drizzly 72 fps with by adding the smokeless and all those danged wads....

Those loads were developed for particular 450 BPE rifles and what the velocities are in those rifles is impossible to say. The owners are in Australia and sent their loads to Kynoch and BPH for testing and paid for them out of their pocket. The above are results from pressure barrels as compared to original black powder loads from the 1880's, the 120 gr. load mentioned above which I failed to identify as such. What one must remember, or have knowledge of in the first place, is that these duplex loads for vintage doubles are not intended to give a big increase in velocity nor even for their often cleaner burning. The intent is to increase the velocity just enough for the barrels to regulate, that is shoot to the same point of aim. It is very rare that vintage doubles can be made to regulate with straight black powder loads using todays black powder, even Swiss or a finer granulation. I've never seen one but have heard rumors of such. They will almost always shoot apart. Thus the need for more velocity, often only 100-200 fps...but sometimes more. It just depends on the rifle. I've worked with several doubles over the last 20 years, mostly mine but also for some friends, and I've never been able to get one to regulate using straight black loads. I wish I could as I would prefer that to duplexing. All have shot apart. The least amount of SR4759 one can use and achieve the desired results is what should be used. I don't recall that I ever got to 10%, let alone exceeded it. It's either lightly duplex a black load or resort to a NFB load, something many of us are loathe to do.

So yes, the 72 fps does seem paltry when compared to a BP load from the 1880's, except that the odds are greatly in favor of the load being at least 200 fps faster than what was achieved with straight black powder of today.

What would make you think the velocity of the 1880's bp load would be some much greater than with the powders we have today?

A chronograph.

Have you chronographed the 1880's laods?

I don't know the exact dates of manufacture but I have chronoed 4 loads of 43 Mauser we were quite sure were from pre-1900. When I was working with my 500 BPE I sacrificed 3 of the 6 loads I had in my collection that we know dated from the 1890's and when I was working with a friends 400 BPE he had 3 rounds we fired. So yes, I have. My results were the same as those of Seyfried, Bell, Hadoke and a host of other writers and fell very closely to published velocities.

What did the chrograph say?

I said what the chrono results were in the last sentence. Look them up. The original ballistcs are available. If you're asking if the old loads had a higher velocity than those loaded with modern powder, yes they did. I have an idea and a suggestion. Instead of querying me incessantly, fishing for something to attack me on as you have in the past, why not buy yourself a double rifle, preferably chambered to an obscure cartridge for which little data exists so you can do nearly all the research yourself and develop loads that regulate. Then pound the gun shows, antique malls and web sites looking for original cartridges, buy them and run them through your chrono so as to confirm original ballistics. Seek out the same books on shooting double rifles I have, subscribe to the Double Gun Journal to learn what research and testing is being done with vintge doubles and the results. Then you'll know for yourself and if your results differ...they differ.