Some primers are hotter than others. Some mag primers are hotter than others.
IME, the CCI mag primers are hotter than, for example, Federal mag primers. Which primers are you using?
The current Speer manual (#14) lists the MAX load with Unique and their 158 grain bullets at 7.7 grains.
I don't know how many you loaded, but I'd pull them and work up a load from about 7 grains with those mag primers.
People got real cautious when the discussion was about switching small pistol primers with small rifle primers. Well, the loading manuals are all pretty clear about working up slowly from a start charge and going back and starting over when you change any component, including the primer.
Here you've got a Hornady bullet, older Speer data and magnum primers. You've got three small changes to the recipe. And others here are probably right about you not having a problem, given you have a stout revolver but who knows unless they've used this exact recipe before?
Speer #14 also lists OAL from 1.570" - 1.575". What's the length of your loaded rounds?
I'd pull them and start over.
FWIW, I am one of the crazy nuts that use SR primers in the place of SP primers in some loads. But I never start with a MAX or above MAX charge of powder with them.
I would have no problem using mag pistol or small rifle primers in a 357 mag load... but with the listed starting charge, not a max charge, of powder. In this case, Speer #14 lists 6.9 as the starting charge for 978 fps from a 6" revolver.