"...But the serial number is gone and no signs of grinding or filing..."
-or it was never there!
Bannerman (?) "bitsa", I think.Made up from parts that were rejected/scrapped/surplus and was never a complete service rifle.
Parts missing, bad fit of buttplate, wood damage where lock has been manipulated, awful fit of Buffington sight slider, missing markings... and that's without having much of a clue about Trapdoors. Experts will surely find more.
Just my moderately informed opinion,
Patrick