Unsure of your meaning of "break away shotgun". If you mean breakdown shotguns like double barrels they continue to make several different models.
Browning, Remington
One might recognize the two names Browning and Remington. They still make 16 gauge shotguns, as do a few other manufacturers.
Browning's web site has a sn search function.
What model is it? Need more infor as Browning has several different types of shotguns.
I can say that Browning started having shotguns made in 16 gauge in the year 1909.Winchester started having the model 12 shotguns made in 16 gauge in the year 1914.so I would surmise that the time frame of 1909-1915 would be the correct time frame for the introduction of the 16 gauge shotguns.
Only the maker knows.
2000 or so
Crescent. H&D, Folsom, Browning, Winchester, Remington
No.None of the browning auto-5 shotguns left the factory with a adjustable choke.This was a after market add-on.
Browning B2000 shotguns in nice shape can be readily bought for under $500.
there is a dedicated web site for browning auto 5 shotguns, google it.
Browning never used the letter B prefix for any of there shotguns serial numbers.