A Massachusetts resident must have a valid firearms license to possess ammunition.   There's a twist... Massachusetts General Laws Chapter 140 Section 122 defines ammunition as:

"cartridges or cartridge cases, primers (igniter), bullets or propellant powder designed for use in any firearm, rifle or shotgun"

In other words, you must have a firearms license to even possess an ammunition component.

As hard as this is to believe, the Commonwealth also regulates the quantity of ammunition and components that you may store in your home.   527 CMR 1.00: MASSACHUSETTS COMPREHENSIVE FIRE SAFETY CODE   regulates the amount of ammunition and components you are allowed to possess. Without a special permit, you can store:

• Not more than 10,000 rounds of rimfire ammunition
• Not more than 10,000 rounds of centerfire rifle/pistol ammunition
• Not more than 5,000 rounds of shotgun ammunition
• Not more than 9999 primers
• Up to (but less than) 16 pounds of smokeless powder
• Up to (but less than) 2 pounds of black powder

527 CMR 1.00 also stipulates that an ammunition storage permit can be obtained from the head of the local fire department.   With a storage permit, you can store:

• Up to 30,000 rounds of rimfire ammunition*
• Up to 50,000 rounds of centerfire rifle/pistol ammunition*
• Up to 50,000 rounds of shotgun ammunition*
• Not more than 9999 primers
• Not more than 47 pounds of smokeless powder
• Not more than 5 pounds of black powder

* Total of all ammunition cannot exceed 100,000 rounds

Here's a tip:   Before you make a trip to the local fire department to get an ammo storage permit, download a copy of 527 CMR 1.00 and print pages 49 and 50.   It's possible that the fire chief may not be familiar with it.