Hello everyone. New member, first post. I have acquired a New Service serial 129xxx which I think puts it around 1917. Gun is excellent. It is in 455 Eley and does not appear to be modified. I think it is an improved model. It has British acceptance marks near the hammer crown over something. There are crosses on the inside of the cylinder face and the same on left side top in front of the cylinder. Grips are wooden and smooth and somewhat unique and appear to be original. The grips have a high "thumb web guard" and there is a lanyard ring. There is only one other marking on the gun other than standard colt new service 455 eley. On the right side plate in front of the trigger there is a possible unit marking, a 3/215. I can only find ref to two possible units so far. A RAF handley page night bomber 215 squadron and a naval reserve inf unit they may have served in galipolli. Can anyone help on the unit marking. Thank you.