Your link isn't even up to date. We have default registration in Mass and the AR platform is banned. Every time we purchase a firearm (both pistols and rifles), either private or through an FFL, it gets registered and we have to detail the serial number/make/model/caliber etc.
"Massachusetts requires all sellers of firearms to report firearms sales and transfers to the Department of Criminal Justice Information Services, which maintains comprehensive records of sales and transfers. See the Retention of Sales / Background Checks Records section for further information. Massachusetts does not, however, require firearm owners to periodically confirm their continuing ownership of firearms or their eligibility to possess firearms."