GREAT topic!
When I was at Ruger one of my assigned engineering projects was working up a smokeless proof protocol for the Ruger Old Army, because WBR, Sr. insisted that even the BP revolvers should be proofed to a suitable design standard, but it was also determined that using black powder to do so was inconvenient from a production standpoint, due to the extra attention required for cleaning, etc.
About that time Walt Kirst started making his Kartridge Conversion cylinders for the Ruger Old Army and I got him to make a cylinder for .45 ACP which I had fitted with transducer and used as a test platform. SAAMI specification proof ammunition for the .45 ACP was a minimum of 25,000 cup as determined by the sample average MINUS 3 standard deviations. Maximum individual proof pressure was about 30,000 as determined by the sample average PLUS 3 standard deviations.
After having established that the Blackhawk Convertible .45 ACP/.45 Colt was fine with full charge .45 ACP (+P not yet being available at that time, 1985-86) the engineering dept. fitted an Old Army cylinder with Kistler conformal transducer and my task was to develop a smokeless cap & ball proof load which would approximate the .45 ACP proof test conditions with separate loading, using available off the shelf components.
I will not give the "recipe" but did determine that to provide SMOOTH P/T traces a 4Fg blackpowder booster dispensed with a flintlock pan charger at the bottom of the chamber was needed to ensure complete ignition of the smokeless charge. Remington 255-grain .45 Colt lead-conicals could be inserted into the Old Army chambers BACKWARDS with a chamber-capacity charge of a common, readily available shotgun powder and that combination would indeed produce 25,000 psia with VERY uniform pressures, and the minute amount of BP residue was not a problem with the normal cleaning procedures used in the plant prior to packaging revolvers and placing them into shipping.
Incidentally, the velocity with a 255-grain lead bullet in 7-1/2" barrel with the proof load was a very uniform 1030 +/- 30 fps. I later standardized on a 15% reduction of that load, substituting a 240-grain T/C Maxi-Ball cast 1:40 tin lead for 880 fps. from my Old Army revolver and in the following years have killed seven deer with it, all one-shot kills.
So, I could suggest that pressure tested .45 ACP data which approached SAAMI MAP is quite suitable as a steady diet in modern .45 ACP revolvers such as the S&W 25, Ruger Blackhawk, etc. Getting 900 fps with a 230-grain jacketed bullet is reality and you can cautiously do so with 255-grain cast bullet using powders such as Bullseye, W231, SR7625, PB, Universal, Unique, Red Dot, Green Dot.
73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia
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