MA still has an assault weapons ban, so the Colt you tried to transfer must not have been a pre-ban gun. It has nothing to do with a manufacturer - only the date the gun was made and the number of assault weapon qualifiers. In other words, you can (and I have) legally transfer a pre-ban Colt AR into MA or purchase a new Post Ban Colt or Bushmaster, etc. AR in MA. Just avoid the goofy dealer who gave you this incorrect information.
The Springfield Armory SOCOM 16 can be transferred into MA, as long as it is shipped with the 10 round magazine. New (post AWB) hi-cap mags are also banned in MA, but you can posses a pre-ban hi-cap mag assuming you have a Class A LTC. In other words, if you have a MA Class A LTC you can buy the SOCOM with a 10 round mag and then buy some pre-ban mags from any dealer.