Best to ask a gunsmith for assistance.
The M69 suffix identifies your 300 win mag as being a browning BAR that was made in 1969.
Around 1500
50-800 usd
300-500m
Browning.com has sn data under customer service.
You need the services of a professional appraiser
Your serial number indicates that you have a Browning BAR that was made in the year 1973 with the suffix of M73 after the serial number.
100-1000 usd
500 - 700
Your serial number suffix of M72 indicates that your rifle was made in the year 1972.
I believe it was from 1962 onward.
100-800 USD