204 is a double-base stick propellant in the 4350 performance range. Often the double-base powders seem to like a little more start pressure from a magnum primer for the most consistent performance. However, the maximum loads of 204 with 150-grain bullets look like they fill the case pretty well, so it may not be necessary, especially in warmer weather.
I don't have personal experience with this combination, so the above is what I'm reading and checking in QuickLOAD. My expectation would not be misfires or squib loads, but rather that velocity standard deviation may be higher than you get with the magnum primer. If you work up to the maximum loads, they will be less prone to this problem than the starting loads. It is not uncommon to find powders for which standard primers produce more consistent performance than a magnum primer does when the loading density is high, but for which a magnum primer produces more consistent performance when there is some air space left in the case.
P.S., Flipping through my copy of the Norma print manual, they seem to use the Winchester Magnum LR primer in all their large primer rifle cartridge cases. Even 30-30 loads with their faster powders like Norma 200 use it. I think they must have got a pile of those primers and decided to stick with them when testing for the American market, so I wouldn't read too much into it.
Their online load data doesn't specify primers at all. So I wouldn't read anything more into the print data other than the WMLR is what they happened to use, and not that it's a requirement.
