My experience, while admittedly rather limited on Browning's, has been they used the old English/European constrictions of from Cyl through Full of 0.0, .010, .020, .030 & .040. Some US makers also used the .010: standard for Imp Cyl. Technically this was Quarter () choke with IC being around .005"-.006".
Most Europeans & the British normally did not use the terms I/C, mod & I/M but used , & 3/4 chokes instead. The more open chokes were then simply fractional of what was considered full. Exceptions were made when aimed at the US market. Prior to plastic shot cup wadding many US makers used very similar constrictions.
As I recall it was Charles Askins the Senior who made the statement you could order a (US) gun with any choke desired. When it arrived it would be so marked, but would be bored Full.
