Value is too difficult to be accurate without seeing the gun. Condition which includes the amount of original finish and original configuration will determine value. Recommend taking it to a gun shop for appraisal.
You will have to call Browning
Call Browning or check the serial number on their website if it is up.
Comparison to known serial numbers.
1970
The suffix of M71 was assigned to the Browning model BAR(Browning semi-auto rifle) which was made in the year 1971 in Belgium for Browning.
By including the serial number in your question.
Most likely, yes.
Impossible to value with only a serial number.
100-1000 usd
1975
Browning did not make the Model 70, Winchester did. Also, the serial number is not a valid Browning serial number for a 7mm Magnum rifle. Please doublecheck your information.
If you are asking about a Browning BAR rifle,then it was made in the year 1968.