Raimey may be correct

[Linked Image from photos.smugmug.com]

'JF' would be Janssen Fils or Janssen Frères, who may have provided the action

Another possibility is 'LLH' of Laurent Lochet-Habran, the primary Belgian supplier of rough forged tubes using steel from Cockerill Manufacture Liegoise

[Linked Image from photos.smugmug.com]

Lots of Belgian makers made Martini-Henrys, and Janssen made pistols and rifles
https://www.littlegun.be/arme%20bel...0i%20j%20k/a%20janssen%20freres%20gb.htm