well I cant explain , mostly because I dont know .
we did a few tests some years ago , we decide to have some barrels to explode.
brass was easy and they spread pieces of scrap metal all over the place , but the bronze barrels just opened up from breach to muzzle almost . we couldnt have an bronze barrel to explode in the same way as an brass barrel did .
I cant say why , but all those tests was of course using bp , then we decided to use nc in one bronze barrel ( R1 ) , then we got the same effect , we spread scrapmetal all over the place again .
the bronze alloy we used was 90% copper and 10% tin
the brass was just an mix of scrap metal , cant guess what alloy that was .
ok today there are a lot of modern alloys that maybe would work as cannon material . and probably also better bronze then the 90/10 I use , but I like to keep it as close to the original as possible .
I know you amercans often use an alloy called gunmetal : 88% copper , 8% tin , 4% zink
I never tried it , so I got no info about it .
all my experiance from cannons is from cast cannons , I have never tried do one by turning , ok I got an good workshop in the basement with both an lathe and an milling machine .
but I am of that opinion that cannons should be cast as they was 400 years ago
but if you are interested in antique gun alloys there is an book from the archaeological research laboratory in Stockholm university , its an doctoral dissertation named : the inception of copper mining in Falun .
written by : Helena Forshell
I got an copy of it from uppsala university just a few years ago , they probably still got it .