It looks like Nashua is a membership-only range. I have just asked them to add me to the waiting list. Are there any other ranges for 300+ yard shooting, ideally within 2-3 hour drive from Boston?
Sunset Mountain Fish & Game Club in Canterbury is right off exit 18 on I-93. They have a 500 yard range. I used to be a member when I lived in the Lakes Region and I'm sorry I let my membership lapse when I moved down to the southern tier. It's a great club!