I believe the new regs define "feeding devices" as anything that is capable of firing a projectile. They are not talking about magazines. They are referring to "guns."
EDIT: As Rogues pointed out below, I'm likely mistaken. I was looking at this section:
SECTION 10. Section 10B of chapter 66 of the General Laws, as so appearing, is hereby
34 amended by striking out, in lines 7 to 8, the words “rifles, shotguns, machine guns” and inserting
35 in place thereof the following words: - feeding devices