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 at http://leverguns.sixgunner.com/topic.asp?TOPIC_ID=16616&SearchTerms=smokeless
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.
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.
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