Can Not use large primers in a small primer pocket, they just will not fit. All the manuals state not to use magnum primers unless called for in load data. However, I have been using Remington 5 ½ primers in 9mm and 38spl for about 32 years without any issue what so ever. Experts (people that say they know more than me) tell me that Rem 5 ½ are magnum primers. Even though Remington does not identify them as such, and there is no definition of what is, or is not, a mag primer. So, I would use the WSPM primers after a careful load work up. But do so at your own risk just like I am.