Blue Book of Gun Values.
By calling or writing to Colt Mfg. Co,. in Hrtfd,CT
Try Proofhouse.com
proofhouse.com
Based on proofhouse.com the 1977 colt cobras shows serial numbers 60001R - 71400R & 1978 as just 63401R????????
Colt factory: 1 800 962 2658............
You will have to call Colt since you did not provid the serial number.
Proofhouse.com has sn tables you can look it up on.
It's under the cylinder swing near the barrel.
You will have to call Colt. Published serial numbers stop at 1978
all colt SAA pistols have serial numbers. If the serial number was filed off then the gun is Illegal to have, and without serial can't tell when made...............
You can find a list of Colt M1911 and M1911A1 production serial numbers at http://www.coolgunsite.com/pistols/colt%20production.htm. Going by the numbers in your question (7071), it looks like you have a M1911 that was made for the Navy in 1912, the first year of production.
Your serial number doesn't have enough numbers. The starting serial number in 1978 was S01001.