Jack: could you please post an ultra close up of the 'HRF' (maybe chalked?), which should be H.R.F. of Heuse-Riga Fils http://www.littlegun.be/arme%20belge/artisans%20identifies%20h/a%20heuse%20gb.htm
That mark has been found on an Ithaca Flues model.
And may I add the pic to the 'AJ Aubrey and Meriden Fire Arms' album? Thanks!