If you want for magnum's one shot ability to be nerfed as well, you can use this mod https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3284675086
It's "[Support] Random Infected HP", which has implemented feature such as "certain chance to one shot common infected" which is applicable for sniper rifles and magnum, it works both ways for simple co-op campaign and realism campaign so hunting\military rifle wouldn't be OP for simple campaign on expert, but also somewhat usefull for realism campaign
Yet again, thank you so much for this collection project