Hi,
Ok here is the deal the 357Sig receiver is stronger in some spots for the round.
So if the 19 does not have this strength you might run into problems.
I would write to Glock and ask them.
Some times it is in a time frame (when built) that it will be plenty strong. But if it does not have the double pin going through the frame it will be weak. It might shoot fine until it does not.
If you look at the 32 and the 19 in the link I put up you will notice the 1 or 2 pin I am talking about, above the trigger.
The second pin is the one that gives it the extra strength to handle the 357 Sig round.
HQ