What would be the advantage of a J "Magnum" frame?
The J-magnum frame is stronger than the J-frame.
Both the .38 Super and the 9x23 lack the case capacity of the .38 Special by a considerable margin and easily fit into a standard 940 J Frame cylinder.
Having more case capacity does not mean that you can fill it to the top with powder, seat a projectile and safely shoot it in the firearm it is chambered for. The 357 Magnum is not more powerful than the 38 Special becasue it has 1/10" more case length.
If you take a magnum frame and convert it to 9mm I don't see how you can call it a 940.
Over the years, the 940 was built on both the J-frame and the J-magnum frame. No one is suggesting converting a standard firearm to 9MM. However many of us have converted firearms to other calibers. My 360PD is a 9x23 revolver now.
I have exceeded the maximum listed data for the .38 Special and 158 gr. SWC in the notorious Speer #8 and gotten "only" 1115 FPS in a Ruger SP-101 with 2 1/4" barrel. How are you getting 1300 FPS with a jacketed bullet in a cartridge that has far less case capacity?
Dave Sinko
Because that is what the cartridge is capable of safely doing.
Powders that make the modern 9x23 Winchester cartridge (born in 1996) powerful and efficient did not exist when the 38 Special came into existence almost 100 years earlier in 1898. The design and strength of the cartridge casings is dramatically different because they are engineered for totally different operating pressures.
Loading a 38 special cartridge (or any cartridge) for pressures that are well above SAAMI specifications is a dangerous venture and I would strongly recommend against it. If you require that much more power from your firearm you should choose a cartridge that is capable of producing it without exceeding safety margins.
According to SAAMI, the 38 Special is designed to operate around 17,000 PSI, 38 +P 20,000 PSI, 357 Magnum 35,000 PSI and the 9x23 operates around 40,000 PSI. I do not care how you look at it. If you take the same projectile and load it in a cartridge at 17,000 or 20,000 PSI it is going to move slower than if you load it to 35,000 or 40,000 PSI.