Add Fitchburg Sportman's Club out in Ashburnham, BUT rifle range is limited to 100 yards and under renovation. Covered shooting stations are planned, preliminary work in progress.
Now, I'm not an officer there and am not an expert on the rules, but I don't think that the Braintree Rifle and Pistol Club has any caliber restrictions. They have a 100 yard outdoor range.
I'm not sure what the regular status of .50's are. We discussed having the 50 there at the pumpkin shoot and the president said, 'if it's legal to shoot in Ma, it's legal here." It's the only time the subject of .50's ever came up as far as I know.
Whether or not the club would like a regular diet of them, is doubtful, just out of consideration for the neighbors .
I recently asked the Chief Range Officer of BRP if .50 BMG was permitted, and the answer was no. He said the NRA, after a recent inspection, deemed the rifle range to not be adequate for the .50 round.
Join Harvard. They love .50's there. As a matter of fact the treasurer and grounds committee chairman started an association of .50 shooters there. After you join, you'll need to be qualified at the 200/300 yard ranges but that's no big deal. You'll do fine.