I've copied and pasted from some old threads where I wrote some stuff on this topic. Here it is:
Those of you who reload black powder cartridges for your antique rifles and pistols may be interested in article written by Sherman Bell in the
Double Gun Journal. In this article, he measured peak pressures for both black powder and some smokeless powders. I've summarized the most interesting aspects of his experiments in the bottom part of this post.
In general, smokeless powder 2400 gives approximately the same pressure curve as black powder
for the same velocity. Smokeless powders slower than 2400 will actually give lower pressure curves than black powder
for the same velocity. Bell indicates that the danger in using smokeless powder is really only the danger of an overcharge or double charge, provided slower smokeless powders are used (another cartridge historian, John Kort, has found that 2400 is the crossover point ... use only 2400 or slower.)
Personally, I have reloaded and shot both smokeless and black powder in my old Winchesters dating from 1882 and on, including the '76, '86, and '94. Based on my own experience, however, before reading Bell's article, I decided that I would no longer use black powder in valuable antique rifles for the following reason: if the barrel has any pitting in it at all, even very small pits, it is impossible to completely get all the black powder residue out of those pits, with the result that the pitting will slowly get larger over the decades. Secondly, with smokeless powder such as IMR 4198, I could get the same velocities as black powder but with lower peak pressure.
I never use smokeless powders faster than 2400 in an antique firearm, not even for light loads ... the pressure peak spikes too high to risk it.
One problem I have found with using slower smokeless powders in some of my old rifles (especially a .38-55 made in 1896) is that the rifle has an oversize bore (.381) and I can only chamber bullets up to .379 without inside reaming the cases. Black powder has a high enough pressure spike to 'bump' up the bullet to fill the groove diameter, but slower smokeless powders like IMR 4198 simply could not produce high enough pressure to do that at original velocities. I found, however, that if I used a faster powder, but still slower than 2400 (IMR SR4759 in this case), I could get enough pressure to 'bump' up the soft lead bullet to fill the groove diameter for decent groups at 200 yards with iron sights.
If 'bumping' up is not an issue because your bore is not oversize, then for some cartridges, you can experiment with slower and slower powders until you find one that gives you original black powder velocities with a powder that fills the case to capacity. I've done this for my .44 Russian and know of other fellows who've done this for their .38-55's and some other obsolete black powder cartridges. The down side of this is that you use more powder (more money) but on the other hand, at least with my .44 Russian, I get very clean and consistent burning.
Bottom Line: With the right smokeless powders, a fellow can achieve original black powder velocities at lower peak pressures than black powder generates, and without the corrosive residues getting into nooks and crannies and tiny pits.
Summary of Bell's article
[FONT=Verdana, Arial, Helvetica] First, before you black powder purists take me out behind the barn and try to knock some sense into me, let me say that nothing can replace black powder when it comes to the BOOM and smoke and the rush I get everytime I fire off a black powder load. On the other hand, I have believed for some time that the right smokeless loads can give as much, or more, velocity with lower pressures than black powder, and without getting "BLACK SOOT IN MY CUSTOM 45-70" as Paco put it.[
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Pretty much all of the info below has come out of an article by Sherman Bell, published in the Autumn, 2005 edition of The Double Gun Journal, 29-42. This article explained or confirmed three things for me:
1. Why I sometimes got such wild E.S. and S.D. with IMR 3031
2. Why black powder 'bumps up' a lead bullet to fill the grooves when smokeless often did not
3. That there are potentially a lot of smokeless loads that will duplicate black powder ballistics, but with lower peak breech pressure.
The cartridge used in the test was the .450-3-1/4" Express. Pressure vs. time for each shot was measured with a strain gauge applied 1" from the barrel face and the signal analyzed and plotted with an Oehler Model 43 ballistic laboratory. Each point in the plotted measurements is an average of 5 shots. I will summarize the most telling stuff below:
A. The original black powder load of 120 grains of FFg produced a breech pressure (peak) of 21,600 psi and a velocity of 1,812 ft/sec.
B. IMR 4198, at the same breech pressure (peak) gave a velocity of 1,952 fps.
C. Reloader 7, at about the same breech pressure (peak) gave a velocity of 2,132 fps
D. IMR 3031, at about the same breech pressure (peak) gave a velocity of 2,030 fps
E. IMR 4064, at about the same breech pressure (peak) gave a velocity of 2,055 fps.
F. The interesting thing was the burning characteristics, shown in the graphs below:
I found this information fascinating. It explained why, for some powders, I did not get an increase in velocity if I increased the charge ... sometimes I would get a decrease. It also shed light on trouble I was having with IMR 3031 in my .45-90. I found that 50 grains of IMR 3031 under a 330 grain Gould bullet was giving me an average velocity of 1,590 but with an E.S. of 541 fps and a S.D. of 175.[:0] However, if I stuck in a single piece of toilet paper, the E.S. dropped way down. I figure the loose powder in that big case was simulating a variation in charge density, depending upon whether it was stacked up at the back, or the front, or spread out along the side of the case at firing.
G. The author stated that fillers or powder retainers are a 'necessary evil' for smokeless powder. They used a cork-gasket wad over the powder, with an air space between the cork wad and the bullet base. Personally I would not touch that with a 10 foot pole ... no air spaces between the wad and bullet for me. In my own experience, I have found that a single, or partial sheet of toilet paper significantly reduces E.S. and S.D. and enhances accuracy. I've used toilet paper quite a bit, but after reading this article, I will be using toilet paper in most of my loads involving straight-walled, BP cartridges, now that I understand better its effects.
H. The author found that some of the best groups were obtained when the pressure matched the original BP presssure of about 21,600 psi. He talked about the load 'regulating' well at this pressure.
I. He found that a good starting load for IMR 4198 was 40% of the weight of the BP load. This seems to be a rule of thumb for that powder for any larger, straight walled cartridge. For Reloader 7, the factor is 47%.
J. The saw-tooth pattern of IMR 3031 and IMR 4064 made it difficult to find an accurate load and, in general, when it came to accuracy, IMR 3031 gave mediocre accuracy. He believes it is because of the 'willy-nilly' way it burns, and that was with a cork wad. I find that when it is loose in the case, it is even worse if there is a lot of empty space. If the case is nearly full, I'd imagine that this problem is reduced somewhat.
K. IMR 4198 turned out to give the smoothest burning curve as charge was increased, with Reloader 7 a little rougher, but a lot lower pressure for a given velocity.
L. None of the burning curves curved sharply upward as charge was increased, ignoring the saw-tooth ups and downs.
M. The only danger of smokeless in BP guns is that a person puts in too much powder. Also, fast powders giving the same velocities may actually produce a much higer peak pressure than BP. That is why fast powders are better at 'bumping up' the bullet to fill groove diameter, but at the increased risk of damage to one's vintage gun.
In general, it seems that slow smokeless powders are safer in old BP guns than BP is, provided you do not overcharge the case. I stay away from faster powders such as Unique. I wish that 5744 and 2400 had been tested. I suspect that 5744 would have done very well. I also believe that 2400 is one of the better smokeless alternatives for vintage BP pistols and use 2400 in my old S&W #3 .44 Russian to give original ballistics of about 800 fps.
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