Not my words but I knew I remember reading it a few months back. Hope this helps
The Remington Model 31 was made in a number of different grades and models. The following list is directly from the Remingtion website. Different grades and models will bring different values with the more rare grades and models obviously commanding higher prices. To determine which grade or model simply look on the side of the receiver, above the serial number and use the codes below.
And, according to the Blue Book, values for the Model 31, depending on condition, model and grade, can vary from $150 to $2,100.
31A
31AC
31AP – Standard Grade
31B – Special Grade
31D – Tournament Grade
31E – Expert Grade
31F – Premier Grade
31H – Hunter's Special
31P – Police Grade
31R – Riot Grade
31 Skeet
31D Skeet Tournament
31E Skeet Expert
31F Skeet Premier
31 Trap Special Grade
31S-D Trap Tournament
31S-E Trap Expert
31S-F Trap Premier
31TC Trap (or Tournament) Grade
31T-D Target Tournament
31T-E Target Expert
31T-F Target Premier