SMLE Barrel inspection stamps

[Bindi2]

You obviously have a Lithgow Rifle or Barrel.
The stars circling an 'A' are view marks, early barrels had four, post 1935 barrels only had two, you may occaisionally find an Inspection stamp with them or if you are lucky, you may have a letter, S, L or K representing the steel the barrel was made from(1 and 2 on early barrels.)
Attachment 59922Attachment 59923Attachment 59924

Hi Muff
Would you explain the S L K and the 1 & 2 please