Hi - this is a quick and hopefully simple one. I'm looking at a 1917 smle that is reputed to have been refurbished (new bolt,magazine, and beech stock during WW2. The barrel has a serial number with the letter 'Y' above it. I'm wondering what this refers to and if this has any bearing to whether the barrel is original to the rifle or not. It does also bear GR inspection marks, which may make this a moot point. Thanks,