[johnneville]

TSA agents are federal employees and federal law prohibits carrying-on ammunition on planes. It is not Boston specific other than that's where OP got caught. You can still check it if you want. I assume the reason is to reduce the chances of accidental discharge causing risk to the plane and/or the prevent one part of a weapon that could be used for hijacking. Even if laws allowed you to take bullets into airports, I have no doubt that the airlines (private business people choose to patronize) would prohibit you from carrying ammunition onto their planes and they'd have every right to do so.