First, AR15s are NOT fed by "clips" . . . they are magazines! Stripper clips feed mags, not AR15s. Little nit that some of us are sensitive about.
Second, to POSSESS any firearm, mag, ammo, or components (including spent .22LR shells) in MA, you MUST have a permit or you are facing a long jail term (treated much more seriously than murder in this warped state).
ONLY exceptions to the need of a MA LTC (NR) is to attend a "match" (organized event for which you have proof with you) or gun show/exhibition. Range visits are NOT exempt!
MA NR LTC cost $100/year and take 3-6 months to process for new or renewal. Although we can hope that the new MIRCS (computerized) system will speed this up, I have no data to prove this to be the case yet.
20 and 30 rd mags are perfectly legal in MA with at least a LTC-B (NRs get issued LTC-A, even better), as long as they are PRE-BAN mags. NO new mags of >10 rd allowed in the state even if you are a visitor, attending a match, have a NR LTC, etc. Possession of >10 rd ("no ban" or LE/Mil mags by non-LE) is a 10 year felony PER MAG!