Like most reloaders, I buy primers by the case and have more than 10,000 in SR alone.
Do you really want to admit that online?
527 CMR 13.04 (2)(c) Storage by Permit
Small arms ammunition primers: private use
Not to exceed 10,000 small arms ammunition primers.
I agree that most competitive shooters probably exceed this, but that is the legal limit allowed a homeowner.
What I learned many years ago is that if you merely prime cases, then they don't count as "primers", allowing you an additional 10K primers that haven't been loaded in cases yet.