Around 1970 based on proofhouse.com.
your colt trooper mkIII was made in 1978.
your colt trooper was made by colt in 1961.
your colt lawman mkIII was made in 1978.
Your colt trooper was made in 1966.
your colt trooper was made in 1962.
Your colt trooper was made by colt at the end of 1968.
made about 1965
Go to proofhouse.com
@1966
The information I have shows that your colt trooper was made in 1961,but it does not show the B prefix to a serial number.
What year is a trooper mark 3 serial 10192j.With the serial number that you have provided,your Colt Trooper mark III was made in the year 1975.
colt diamond back is was made in 22lr & 38 special.with a ventilated rilb barrel. the colt trooper was chambered in 357mag. without a vent rib barrel.