I can't offer a solution, but I think that before diving into interpretation it would be helpful to consider WHY the markings are placed where they are? Any kind of rack number, ownership marks or other such public statements ("This is OUR rifle") would surely be placed where everyone can see them?
Marks on the bottom of the barrel or - and this is really extraordinary - on the inside of the floorplate, where no-one can see them without dismanting the rifle, are therefore hardly ownership marks but something to do with parts/assembly identification.
And just to muddy the waters even further, I would be cautious of assuming that they are Kanjis of any kind. In fact, to my eyes they look more like Naga (North-East India) characters!
Or how about reading them from top to bottom - I see PHIL... in a kind of runic script...