It might be mounted with staking or soldering. A little merchandise is that the pin which retains the firing pin spring cap tended to operate free, and needed to be tapped again in place as just one observed it project from your rear with the bolt. Winchester replaced that pin https://highimpactrounds.com/product/winchester-super-x-12-ga-2-75in-1-oz-8-lead-1290-fps-25-rd-box/