I dug out the old November, 1935 American Rifleman when Elmer Keith tested out a Smith .357 with an 8 3/4 inch barrel. Elmer stated that the 158 grain bullet and that the powder charge was approximately 15.4 grains of 2400 with a muzzle velocity of 1,518 fps. One thing to point out is that 2400 from 1935 will not have the same burn rates as 2012 era 2400. I would very carefully work up to that 1,500 fps mark and use bullets of a decent enough BHN to avoid the leading problem.
The commonly seen assertion, that modern 2400 has a faster burning rate than in days past, is urban myth based on false assumptions. There is no evidence whatsoever to support this claim!
Quite to the contrary, given the assumption that published velocity data going back to 1935 is accurate there is evidence that the burning rate of 2400 has not changed except within the normal bounds of lot-to-lot variation. Back "In the day" ammunition testing was typically done in actual production firearms, and the electronic "counter chronograph" was by then a reality, although much different from the ones available today, expensive, and terribly inconvenient to use. There is no logical reason to question the reported velocity as reported in the above post having Elmer Keith as the reporter of the data.
This said, my own tests, over several years and several chronograph sessions with two guns with 8 3/8" barrels, using the virtually identical load of 15.3 gr. 2400, 158 LSWCGC which approximates the original factory bullet, produced an average velocity of 1518 FPS, only 3 FPS different from Keith's reported result, and the factory published velocity! There simply is no room for there to be a measurable difference in burning rate, as, if there were, there would be a concommitant variation in ballistic performance, which there is not!
The fact that there has been a reduction in published loading data is true. It is not because of changes in the propellants, but rather a difference in the methods by which firearms pressures are measured. This is the change from copper and lead crusher testing, where maximum pressures were interpreted from the deformation of a "crusher" which was physically measured and the pressure them estimated based on several assumptions which were not absolutely correct. The change to measuring by piezo-electric and later strain gauge methods gives different figures, but the added benefit of being able to record the pressure curve as the projectile moves down the barrel. In most cases the pressure standards developed from crusher data, originally referred to as PSI, now called CUP or LUP to avoid confusion with the absolute pressures now possible to measure accurately and referred to as PSI, or, more correctly, PSIG.
In the situation noted above, for most cartridges, the new measurement methods give higher pressures that the older method. The SAAMI MAP standards generally were not changed, but factory loading standards were revised to produce ammunition to the same pressure standard, but measured by the new method.
Let's use .38 Special as an example. The old pressure standard was 15,000 PSI(Crusher), but the old loads gave 17,000 PSIG by the new measurement method. Loading standards were reduced to maintain the original MAP pressure, but measured by the new method. Result, reduced velocity at the same nominal pressure level. Now, by a review of loading manuals going back to the 1950s you will find various reported pressure standards for .38 Special, from 15,000 PSI to 17,000 PSI. So there are discrepancies in what to base estimates from. Let's use the more recent information, 17,000 PSIG for standard pressure and compare this to the generaally used +P standard of 18,700 PSIG. This is only 10% pressure, which translates to
approximately 5% velocity increase. There may be a degree of truth in the assertion that current +P ammunition is no more powerful than older, (pre +P standard), ammunition, but it is s direct result of the change in method of measurement rather than "Dumbing down" standard loads directly. The true reason for +P to begin with may be to be able to continue to load standard ammunition to the existing SAAMI standards while creating a new standard, +P, that really does correspond to the original pressure levels as measured by crusher equipment.
The hard truth is that the majority of ammunition did not, and does not develope the velocities claimed by the factories, so how can a true comparison be done? Maybe one day when the shooting public has pressure testing capabilities equal to current velocity measurement abilities.
