I have been following my Hornady manual which calls for magnum primers for 357. I read on here that it is not needed. Am I running the risk of hurting my guns following my manual?

Not at all.

Mag primers burn a bit hotter and longer than standard, ensuring that larger magnum powder charges are burned completely.

While it has certainly been proven that standard primers will indeed do the job, and you can certainly do just that, using mag primers will not hurt your guns.

I'd follow what the manual recommends. A lot has to do with the amount of powder to be burnt. The magnum burn a little hotter and a tad longer than a normal primer. Some powder charges for the magnums can have a lot of powder grs. You could get by with low volume load with a normal primer but for the high volume loads you need the extra push of a magnum primer to burn everything.

The powder manufacturers make specific recommendations about which primer to use. Magnum primers are only recommended for heavy loads of slow burning ball powders. You won't get in trouble following Hornadys load recommendations because they pressure test their loads before publishing them, as do almost all component manufacturers. There are some companies that only manufacture tool & accessories, and personally, I usually avoid their data, but there are some notable exceptions to this personal rule, such as Lyman & RCBS, who often list the pressure data for their loadings.

I'm not sure which companies you're referring to, but Lee Precision only offers data already published elsewhere, and does not claim to work up data on their own.

Kinda depends on what powder you are using????

Hodgdon Powder data lists the use of Mag primers for any of their 357 loads regardless of the powder even though some of those powders do not "require" a mag primer such as HP 38/W 231. For their powders only H 110 and W 296. I called them about this and was told they tested all with the same primer for constancy in load data. If it is a Magnum they tested with a Mag primer if it needed it or not.

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