It looks like the rifled tube was proofed twice. There looks to be an "8.9" stamp near the lower ribe and then an "8.8" stamp closer to the intertwined "EL" proofmark. There's also an "Express" stamp so I'd guess 360 BPE Express but it wouldn't hurt to make a wax cast and make some measurements. All those proofmarks don't appear to be Belgian. Can you snap a better pic of the flats of the rifled tube?

Kind Regards,

Raimey
rse