Larry;
I took my figures from the Alliant manual. They agree with your numbers with the exception of the 3-1 12ga. The higher velocity given for 16ga over 12ga would be accounted for by the fact if you put the same powder charge under the same shot wt in a smaller bore higher pressure will be generated so a higher velocity obtained.
Alliant lists for the 16ga as follows;
2½-1 = 1165
2 3/4-1 =1220
3-1 = 1275
2 3/4-1 1/8 = 1185
3-1 1/8 = 1240
3¼-1 1/8 = 1295
3¼-1¼ = 1185
These have all been industry standards for as long as I can remember, including the 3-1 in 12ga @ 1255. I am thinking Win may have made a misprint on that one & meant it to be for the 3¼ de load. I cannot recall having even seen a 3de-1oz factory load for many a year now, they seem to have been totally replaced by the 3¼de load in deference to the autos.
I agree, the marking system has been long overdue for an overhaul. The BP equivelents have little meaning except to a handful of us old timers anymore. "US" refering to me & any others which still enjoy burning a little charcoal along.


Miller/TN
I Didn't Say Everything I Said, Yogi Berra