If you enjoy the forum please consider supporting it by signing up for a NES Membership The benefits pay for the membership many times over.
What is the penalty for having/being caught with a pre-ban high cap.
Did you mean pre-ban, or post-ban? Post-ban penalties are described in MGL Ch 140 Sec 131M. Having a pre-ban high cap isn't illegal, you just have to have a LTC-B for rifles/shotguns or an LTC-A for handguns.
Not precisely but you're on the right track- large capacity magazines, even if preban, are "controlled devices"- meaning you must have an LTC-A or an LTC-B to even possess one in MA.