Howdy
I cannot speak for California, but perhaps somebody who actually lives in Massachusetts should answer this question in regards to Massachusetts.
It has nothing to do with internal locks.
In October of 1998, the then Attorney General of Massachusetts decided he did not like the safety features available on many commonly available handguns, so he came up with a list of features that any handgun sold in Massachusetts must have to be legal for sale in Massachusetts. Looking back, the most important feature was that the gun should survive a drop test without firing. There were other features, such as a non-removable serial number located somewhere inside the gun, and a minimum required trigger pull. I seem to remember there were stipulations regarding no pot metal being used too. But the biggest issue was the gun must survive a drop test, by being dropped from a certain height onto the hammer with a round under the hammer. Ruger's transfer bar designs easily pass this test, but no traditionally designed single action such as a Colt or one of the Italian replicas would pass this test. Even if the hammer was placed on the so called 'safety cock' notch, being dropped from any height onto the hammer would shear off the notch, or shear off the sear, and the gun would fire.
The other requirement is in order to become 'Mass-Compliant' the manufacturer must supply examples to be tested at an independent testing laboratory. The guns would be tested to destruction. Not only that, but every variation of each model must be supplied. Since many firearms carry different different model numbers, depending on their barrel lengths or other features, Mass cleverly required every single model to be tested to destruction, even though the only difference might be something as simple as barrel length.
Colt and Uberti simply did not supply any handguns to be tested. They reasoned that the market here was not large enough to justify this 'investment'. So in addition to the fact that the guns would not pass a drop test anyway, Colt and Uberti single action revolvers are not legal for sale in Massachusetts.
Ruger, on the other hand, (god bless them) supplied models to be tested, and furthermore called the AG's bluff (he was going to fine gunshops $5,000 for each 'non Mass-Compliant' handgun sold). Ruger sent the AG a letter saying their firearms would pass the tests, and furthermore, if the AG tried to prosecute any dealers for selling Rugers, Ruger's lawyers would go to bat for them.
Consequently, the only single action revolvers us CAS shooters are able to buy new in this state are Rugers.
This cowboy will never say anything bad about Ruger because of the stand they took on our behalf.
Here is a link to the AG's list of Mass Compliant handguns. Take a look at how many are Rugers. Don't forget that these manufacturers had to submit one of each of these models for destructive testing.
https://www.mass.gov/files/documents/2018/05/29/Approved Firearms Roster 05-2018_0.pdf
Even so, not every handgun Ruger makes is on the AG's list. I would like to have one of the medium frame 44 Special Blackhawks, but Ruger must have decided they would not sell enough here to make it worth their while, and they are not on 'the list'.
P.S. Gun enthusiasts took the AG to court, but the court sided with the AG. The one stipulation the court made was that a handgun legally registered in MASS before the October 1998 date was grandfathered in. Believe me, there are not a whole lot of those.
