Losing Power: .38s in .357s
Looking through Ken Waters's Pet Loads, i ran across some test results that are worth noting.
When he fired some .38 Spl +P loads through a .357 cylinder, he actually lost around 70 fps compared to the velocity obtained with a .38 Spl cylinder.
In some ways that's no big deal. Even a standard .38 Spl. will get the job done for CCW or home defense. But it does affect the load choice if 38 +P rounds are carried in a .357 revolver for defensive purposes.
The 125 grain JHP is a legendary load in the .357. It is a consistent stopper. Velocities can exceed 1600 fps in an 8" barrel. It takes a tough bullet to ensure adequate penetration at those speeds. Many 125 JHP loads for the 38 +P load go about 975 fps from a 4" barrel and so will barely break 900 fps if fired from a .357 cylinder.
A tough 125 JHP which gives good performance at 1600 fps probably won't expand much at 900 fps. If .38 +P load uses the same bullet as the .357, you are really just shooting a 125 grain round nose.
At the same time, the .38 loads are attractive defensive loads because they have less muzzle flash and muzzle blast than the magnum. This matters in the dark, confined spaces where defensive shootings take place.
There are two solutions. One is to choose .38 +P loads that were specifically developed for snubbies (like the new Gold Dot 135 JHP). Another is to use a 158 grain LSWC which does not depend on expansion to be effective.
This performance is also an excuse to save money. If you know you are going to use 38 +P rounds as your primary defense load, you can buy a 38 Spl. revolver instead of a .357 magnum. A good used Ruger or S&W 38 will cost half the price of a new .357 and will often be $50-$100 less than a used magnum. That sounds like a deal to me-- spend less, get better performance.