Anyone know this R.L.R. marking?

[Gil Boyd]

As it looks like a separate stamp mark it may be nothing to do with the rifles progress through PH or other manufacturers. It could be simply something like an identifier for the Royal London Regiment(s)
Just a suggestion which may be wide off the mark, but there are other Regiments which operated in Canada such as the Lambton Regiment (LR)which again could be closer to the mark and associated with teaching shooting to grammar schools and other training establishments. I know certainly that the Royal Regiment of Fusiliers who were renamed in its past spent a great deal of time in Canada too
Gil