casulman454
Man, you do in fact ask a lot of questions! No problem though, let's go through them.
"I want to know how you go about working out a duplex load for a given bullet. Do you do it by percentages of powder weight or bullet weight?"
It is by percentage of powder weight. There are different definitions of "duplex load" For this discussion what I use for duplexing BP cartridges is for the principle use of decreasing bore fouling left by the BP and increased accuracy over a larger number of shots. Keep in mind that for a limited number of shots straight BP loads are tough to beat accuracy wise but good duplex loads are as accurate and they keep the bore fouling down. I do not duplex to increase power or get higher velocity.
"How do you select a powder to do a duplex load with?
I have tried other powders but have gone back to the "standard" which is 4759. With its' characteristics of ease of ignition, burning rate and bulk I have found no other powder that works as well. I did not make this discovery but only use what others before me have recommended and used.
"Do you use smokeless with the BP as part of a duplex load or a smaller grain (faster burning ) BP in the duplex load? "
I use smokeless. However, I have flirted with using 4F under Cartridge but have not shot enough to get into that discussion.
"Is there a discussion of any of this where I can read it and if so, where? I wouldn't know where to even start and I want to know that in case I want to try it too."
Yes there is a very good source of information. Wolf's book on replicating 45-70 loads for trapdoors has a good explanation of it.
"I keep hearing the term "volume equal." Now to me that means that if I'm using my volume measure for let's say 90 grains of FF-G black powder in my 50 Caliber Hawken ( as is the recommendation from TC) and it says on the Pyrodex can "equal volume with black powder", then all I have to do is pour Pyrodex into that same volume measure that I used for the BP and it'll work out to be near the same. I don't have to actually use my powder scale. Is that a correct reading of it and if not, please explain."
Yes, that is a correct reading of "equal volume regarding loading for BP.
"Now lets say that a load manual calls for 62 grains of FF-G powder to be used with a given bullet. I am assuming that is talking about 65 grains weighed on a powder scale. Now I pour that down the 30 to 36 inch drop tube slowly and it goes in my case. Now if the bullet is to be seated at the spot where it is supposed to be seated but in order to do that the powder in the case must be "compressed" then whatever the distance is that you have to "compress" the powder is the compression distance? It it mandatory then that you seat the bullet where it supposed to be seated? I mean where you would normally seat it if nothing was in the way like powder in the case."
There is what is called a "compression ratio". But to keep it simple you must compress the powder to the base of the seated bullet. This can be done as a separate operation with a compression die if considerable compression is done. It can also be done when simply seating the bullet if the charge requires only 1/16th or 1/8th compression.
"And if you wanted to seat the bullet out further, as long as there was no space between the bullet base and the top of the powder column, then all that would mean is that the "compression" would be less. Is that right? So it seems that compression is dependent on how much powder you load and how well in goes in the case down the drop tube and where you seat the bullet ( and on the length of the bullet itself of course) and all of those are variables."
Yes, that is right. There are some differing thoughts on the "never leave airspace in a BP load rule" as not being hard and fast but let's not go there at this time. For duplex loads no air space is a must and there needs to be at least a little compression. This is necessary to prevent mitigation (mixing up) of the 4759 into the BP. Seating the bullet out would lead to less compression for a given charge but then the compression ratio may not be correct and require a larger charge at the same time to get the correct compression ratio. I do not use a drop tube as I have found no improvement in accuracy, it is not required to get the charges of powder (70 gr in a 45-70 case) I use into the case and I consider it to be more "witchcraft". Bear in mind I am talking about loading for the 45-70 here, I have seen where the use of the drop tube is beneficial in some cartridges to "settle" the powder charge so little compression is required. With compressed powder charges in the 45-70 I have seen no benefit to the use of a drop tube. With duplex loads a compression ration is not important as long as there is compression.
"So if I use a 480 grain bullet with a GC, load with 1.5 Swiss. my load would be the amount of powder that it will take to make the top of the powder column be about 1/16 to 1/8 inch higher than the bullet base when it is seated to the "Normal" depth in the case. My compression would be either 1/16 th or 1/8 inch(usually expressed in hundreds or thousands of an inch). If that amount of powder is generally consistent with what the loading manual says is the correct amount of powder for that bullet, we ought to be somewhere right with the starting load anyway. Of course, we will adjust each of the other variables ( primer, bullet seating depth and compression, bullet hardness or alloy content, lube, powder charge, and how far off the lands the bullet is when chambered) one at a time to see if a change will result in better accuracy. "
Let's not add too many variables here at one time. Yes, that technique may give you a good "starting" load but it may not be the best load as the compression ratio may be incorrect. It may also be your only option if you are depending on the bullet to compress the powder. Let's say we have our cartridge OAL set so the driving band is barely engraved when a cartridge is chambered. We then measure the seating depth of the bullet and know that with a compression die we must compress the powder to that depth regardless of the charge. Then take your load of 62 gr (or was it the second stated 65 gr?) and load up 10 cartridges. Then increase the charge 5 gr to 67 and load up 10. Then increase the charge to 72 gr and load up 10. Go to the range and test them at a preferred 200 or 300 yards. Obviously the best grouping and most consistent (over the chronograph) load is the one to use as that will be the load with the correct compression ratio. Obviously if you change the seating depth the compression ration changes and you may have to start over. That all applies to straight BP loads not duplex loads.
"That is not so different than what I have always done loading smokeless powder except that the loading manuals will always give me minimum and maximum loads for any given bullet weight."
That is true about smokeless. Wondered the same about BP myself.
"So this shouldn't be something that is a LOT of difference from loading smokeless. I guess it's just not having the comfort level that I have with smokeless that is giving me the hebbie jeebies and causing all of these questions. Stick with me here and I'll come around."
Not a lot different but some. Actually very little difference when the witchcraft is weeded out. Some difference in technique but not much.
"Right now I just want to get some loads worked up and ding some gongs. But as I become more accustomed to the whole BP scene, I want to know what is possible to be done. "
Well ok, now we're talking! Let's get you started; In Wolf's book he explains that for duplexing 1 gr of 4759 is equal to about 3 gr of 2F or 3F BP. (this is not a volume thing, it is a by weight thing, and should not be used in any other loadings.) I have found 4759 to equal about 2.5 gr BP with Goex Cartridge. So for a starting load for every 1 gr of 4759 we use we are going to reduce the BP charge by 3 gr. In a real 45-70 we are talking about a 70 gr charge of BP so we will go from there. Notice here we are reducing the BP by an equivalent ratio (in power) of the smokeless 4759 we add. The working pressure of the duplex loads should be close to the straight BP loads and the velocity will be close to the same also.
Get some 4759. I have not used the Swiss as I mostly use Goex Cartridge. However, the Swiss should work ok. Put 7 gr of 4759 in the case first, over the primer. I say to use 7 gr because I know that will work as a standard charge of 4759 with full charges (the reduced equivalent) of BP in the 45-70 with longer barreled rifles. The case may be FL, partial or ND'd. I neck size. I use Rem nickeled brass with WLR primers but use what you normally use. To compute; 7 (4959 charge) x 3 (3 gr BP = 1 gr 4759) is 21 so we will subtract 21 from 70 (full BP 45-70 charge) and put 49 gr by weight (70 -21) of BP into the case on top of the 4759. With a cartridge OAL that just engraves the lands using your 480 gr bullet, the seating depth should very lightly compress this load. You may not want to use the drop tube here as no settling is required. An over powder wad may be used if necessary but I've not found them necessary either. You should have 10 cases charged this way. Seat the bullets to the cartridge OAL ensuring there is slight compression to prevent any mitigation of the two powders. I also do not crimp as it is not necessary for better ignition with duplex loads. I use a taper crimp die to even out the flair of the case mouth.
Next load increments of 10 cartridges increasing the BP charge 2 gr at a time until you have increased the BP charge to 56 gr by weight. These increments are all over the same 7 gr of 4759. All of the bullets are seated to the same OAL. The compression will increase with each increment. Load 10 cartridges of each increment.
I use 7 gr 4759 and 54 gr Cartridge with a Rapine 460500 500 gr bullet in my TD and find that a compression die is not necessary for this load. The bullet will compress it with no distortion to the bullet. Go to the range and test the loads. I'll bet you will be amazed at the accuracy and uniformity you get. Oh yeah, don't need no stinking blow tube either!
The smokeless charge not only provides better ignition but is purported to blow the fouling out of the barrel. This is evidenced by trying increasing charges of smokeless 4759 while decreasing the BP charge the appropriate equivalent. If you look down the bore from the breach end after firing 3 regular BP rounds you will see thick BP fouling at the breach and streaks of BP fouling going toward the muzzle. Remember this is the fouling of the BP and it accumulates the thickest at the throat. This is why most purists like to use blow tubes to keep this fouling soft so cartridges with bore riding bullets can be chambered. If you started at 5 gr 4759 and 55 gr BP and fired 3 shots then looked down the barrel you would see little fouling at the throat and some "streaking" about half way down. Go to 6 gr of 4759 and 52 gr of BP and you would see fouling in about the last 1/3d or 1/4th of the barrel. With 7 gr of 4759 the BP fouling is blown out of most 28-32 inch barrels even with upwards of 60 gr of Goex Cartridge. Now there is still some fouling but it is not the heavy crusty, streaky kind you get with just straight BP loads. I have fired 125 rounds through my TD without cleaning using these loads and the bore was no dirtier than after the first three shots and just as accurate with the last 10 as with the first 10.
One caveat; a good BP lube is still required. SPG works great or you can make your own. There's a lot of witchcraft involved in BP lube formulas also but I use Wolf's beeswax and olive oil formula. Simple and every bit as good as SPG, maybe better because it costs a lot less.
That's the down and dirty of it. I expect to hear some howls and screams from the purists but they have their game and this isn't it, so I let them howl while we go shooting. Quite simple really, no mystery, no witchcraft but lots of good shooting pleasure. Kind of like my younger brother Mel said in a movie; "No games, just sports!"
Larry Gibson
