There is so much misinformation in this thread that it’s getting hard to keep fiction from reality.
Threads like this give forums the bad reputation for finding information.
Bottom line, the modern .38 special case is shorter than the modern .357 magnum case and that is the only serious difference between the two.
It's little wonder that the older names here are hardly posting anymore.
That's what I was thinking.
You can load your modern .38 spl cases to the same specs as .357 magnum. However, unless you have a ballistics lab in your closet, there is no way for you to tell when you have reached that point. You will want to find the .38/44 data mentioned above and make sure you work up to it carefully. A lot of this data is older and was meant for older cases that had more empty space and this will cause the pressures to be a little higher than when originally tested.
The main concern, which was brought up above, is what if they found their way into a .38 spl? One of the advantages of reloading is that you don't have to follow SAAMIs suggested specifications and can load for a specific firearm if that is your wish. If there is a danger the ammo might end up in a firearm other than you intended, I would highly suggest you get some permanent markers and color the case heads red on any ammunition that is loaded to higher pressures than the headstamp dictates. And if you store them in boxes mark the boxes in red also and explain why they are different.