Ridgeway, what's makes you believe people will comply with such a law?
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People have thus far complied en mass to every gun control law, confiscation, tax, and registration.
I don't see even the "cold dead hands" people putting up a fight for standard cap mags, nor goon squads collection them. But who would risk 10 yrs in jail just to keep a LEO marked 17 rd glock 17 mag for plinking @ the range if such an item becomes illegal? Who would risk a cop seeing and actually knowing? Or it being discovered in a dui checkpoint or some other such scenario.