Finally

 I listened to Cal. Dep. A-G question Prof. Saul Cornell about how pre-1789 laws provided analogs to California's Unsafe Handgun Act, which requires a drop test different from the industry standard and therefore another cost to add to getting a handgun on the roster of lawful for civilians to buy handguns.  (Police can buy whatever "unsafe" handgun they want.)  It also requires a magazine disconnector and a loaded chamber indicator that makes me think of either the 1960s Batman TV show (with the garish effects around the words "POW!!!") or the Mask.  Fine for TV but not really needed on a gun.

His analogs?  Massachusetts adopted a barrel proofing law, you fire a ball with 4x the usual charge to verify it is safe.  Gunpowder storage laws that limited how much black powder you could store in your home instead of the public magazine, 28 pounds and 30 pounds being typical limits.

Fortunately, I was able to respond to Cornell's claims and it was fun in an exhausting sort of way.  His Exh. 24 included the New York City gunpowder storage law.  But the actual law is at 2 Laws of New-York 191-93 (1792), and he copied from volume 1, a law organizing city governments.  He did not even read it carefully enough to notice.  You lucky California taxpayers are paying $500/hour for that expertise.

He claimed that proofing law from 1805 was passed in the biggest gunmaking state in America.  So I pulled the 1810 Census of Manufactures and Massachusetts does not even have any makers.

There are criticisms that this 1810 census was not very complete.

The 1820 census lacks the state by state summary, but I went through each state county by county, and Pennsylvania, Tennessee, and Virginia have lots of pistol and rifle manufacturers.  Massachusetts lists one: Springfield Arsenal.  The 1805 proofing law exempts any barrels made for the U.S. government, so the law did... nothing.

He claimed that low murder rates in the period around the Constitution was because no one kept black powder guns loaded, to avoid water damaging the guns or the powder.  This is vey logical, but it appears the people of the time did not agree.  Mass. Gov. Winthrop's Journal has four incidents of guns not about to be used going off, killing a 5-year-old, and an 8-year-old.  Another unloaded musket at a militia seriously injured three people.  Four incidents in one book.  And the piece de resistance, a law prohibiting Bostonians from keeping loaded cannon, hand grenades, and firearms in their homes.

Odd that you would need that law if people did not load guns until they were needed.

The range of mistakes was just overwhelming.  Hard but fun.