POSSESSION means just that! It doesn't matter if one is a Resident or NOT. The only exceptions for Non-Residents are if they are going to a documented match (not "going plinking"), attending gun shows, LEO, etc. If you can't prove it and the cop doesn't cut you a break, you could end up spending a lot more time in MA than you might like. MA treats gun ownership, ammo, component, etc. infractions much more seriously than rape, murder, burglary! Being hard on gun owners is good for anyone with political aspirations (ask John Kerry, Ted Kennedy, etc.).
Yes, I am aware of one incident where a teenage girl was driving her Dad's car, was stopped and a spent shell casing rolled out from under the passenger seat. The cop was itching to arrest her for "illegal possession of ammunition components", but was foiled since the 18 year old girl had an FID card. This is why I've insisted that my Wife (who hates guns) keep a current LTC . . . every time she tells me that she only does this because I insist on it, I remind her that if I didn't insist she could land in jail for 5 or 10 years for something that is a "yawn" in Free America.